Grain Silo, Bulk Handling Terminal, Flour Mill, Stockfeed, Animal Protein and Pet Food Manufacturing HVAC Duct Guide

Why grain, flour, feed and pet food HVAC is its own discipline

HVAC ductwork for the grain-to-feed-to-pet-food value chain sits at the intersection of four engineering domains that almost never appear together anywhere else in Australian process industry. The first is combustible dust — wheat dust, raw grain dust, milled flour, bran, pollard, soybean meal, finished stockfeed pellets and pet food kibble fines are all classified St-2 or St-3 under NFPA 660, with Kst values that routinely test above 200 bar metres per second. The second is hazardous area classification — every silo headspace, every elevator leg, every transfer point, every pneumatic conveying termination and every solvent extraction column carries an AS/NZS 60079 Zone 1, 2, 21 or 22 boundary that drives motor selection, instrument selection, ducting bonding and fan classification. The third is food safety — flour for human consumption is FSANZ-regulated and feed is AS 5812-regulated, with HACCP-aligned segregation requirements that drive the duct material selection, the surface finish, the cleanout access and the as-built validation. The fourth is odour — rendering plants, pet food coaters, fishmeal handlers and tallow load-out points generate odour streams in the parts-per-billion range that have to be captured at source, transported through dedicated ducting and abated through regenerative thermal oxidisers, packed-bed wet scrubbers or biofilters.

Get any one of those four wrong and the consequence is not a comfort complaint. It is a flash-fire through a flour mill basement after a static spark on an ungrounded duct, an asphyxiation event in a phosphine-fumigated silo because a damper failed open, a recall on a tonne of stockfeed pellets contaminated by carry-over from a medicated feed run, or a neighbourhood odour complaint that closes a rendering plant during the seasonal beef offal peak. Australian regulators have all four on their radar after the global string of grain elevator and flour mill incidents over the last forty years — the General Foods Banks Mill at Cambridge in 1981, the DeBruce Grain elevator in Wichita in 1998, the Imperial Sugar Port Wentworth refinery in 2008 and the regular sequence of smaller Australian grain elevator deflagrations recorded by Worksafe Victoria, SafeWork NSW and Worksafe Queensland through the harvest seasons of the 2010s and 2020s. The Imperial Sugar event in particular — 14 dead, 36 injured, secondary explosions propagating along an entire packaging conveyor — is now the standard global case study in every Australian flour mill HACCP and Process Hazard Analysis.

This guide consolidates how SBKJ specifies and fabricates duct for each zone of a working grain handling, flour milling, stockfeed manufacturing, rendering and pet food operation. It applies whether the site is a 50,000 tonne country silo north of Dubbo, a 600,000 tonne Newcastle export terminal under the GrainCorp shiploader, a 1,500 tonne per day roller mill at Manildra, a 200 tonne per day pellet line at Ridley Pakenham or a 40 tonne per hour kibble extruder line at Mars Petcare Wodonga. The physics is the same. The duct gauge, fabrication tolerance, material and explosion-protection device class change with the scale and the process.

The Australian grain-to-feed-to-pet-food industry — what we actually build for

To specify the right ducting you first have to know what kind of facility you are building for. The Australian grain-feed-pet-food sector splits into six clear tiers, each with a different HVAC profile, regulatory stack and explosion-risk envelope.

Tier 1 — Bulk grain handling and storage

The bulk grain receival, country storage and export terminal sector is the largest in tonnage terms. CBH Group, the Co-operative Bulk Handling growers' co-operative based in Western Australia, is the biggest by tonnage with port terminals at Esperance, Albany and Kwinana plus more than one hundred country silos across the WA wheatbelt. GrainCorp Limited (ASX:GNC) is the dominant eastern Australian grain handler with port export terminals at Newcastle, Mackay, Brisbane, Geelong and Portland and a network of 160-plus inland silos through NSW, Queensland, Victoria and South Australia. Viterra, the Glencore subsidiary, dominates South Australian grain handling with terminals at Port Lincoln, Wallaroo, Inner Harbour Adelaide and Outer Harbour. The Australian Bulk Alliance carries the AWB legacy positions. Cargill Australia, LDC Louis Dreyfus Australia and COFCO Agri operate multiple inland and port positions.

A typical regional country silo holds 5,000 to 50,000 tonnes of stored grain split across multiple cells, with truck receival peaking at over 1,000 trucks per day during the November-to-January harvest window. A typical export terminal holds 200,000 to 600,000 tonnes across the cell battery with a ship-loader rated at 1,500 to 4,000 tonnes per hour. HVAC at these sites is dominated by three duties: the truck receival dust extract serving the dump grate and primary cleaner, the elevator leg and transfer point dust extract serving the vertical bucket conveyor train, and the silo aeration plenum that pushes 0.5 to 2 litres per second per stored tonne of cool air through the grain mass to suppress insect and mould activity. The combustible dust hazard is severe because grain dust is St-2 to St-3 Kst 130 to 220 and elevator legs are the highest-frequency historical ignition location in the global grain industry.

Tier 2 — Flour milling for human food

The Australian flour milling sector serves the bakery, pasta, biscuit and food service chain. Mauri ANZ, owned by Lendlease through Allied Mills, runs the largest network including Picton and Maitland NSW, Tennyson SA, Forest Hill VIC and Mt Sturt NT. Allied Pinnacle, the joint venture combining Manildra and Allied positions, operates a parallel network. Manildra Group, owned by the Honan family, runs the largest single mill at Manildra NSW plus operations at Gunnedah and Sydney and includes the Shoalhaven Starches downstream operation as Australia's biggest flour miller and ethanol producer combined. Defiance Mills runs the major Toowoomba QLD position. George Weston Foods operates flour milling integrated with its Tip Top bread and bakery businesses. Mungo Industries operates a private SA position. A modern Australian flour mill grinds 200 to 1,500 tonnes of wheat per day on a roller-mill, sifter and purifier train, producing white flour, wholemeal, baker's grade, biscuit grade and the bran and pollard by-product streams that flow into the stockfeed sector. The HVAC challenge is dominated by flour dust at higher concentration than any bakery, with NFPA 660 St-3 Kst above 200 across the whole roller floor, sifter floor and purifier floor.

Tier 3 — Stockfeed manufacturing

The stockfeed sector takes grain by-products, oilseed meal, animal protein meals, vitamins, minerals, medicated additives and a long list of minor ingredients and turns them into pelletised feed for the cattle, sheep, pig, poultry, aquaculture and equine sectors. Ridley AgriProducts (ASX:RIC) is the largest national operator with mills at Pakenham VIC, Wasleys SA, Lethbridge VIC, Tamworth NSW, Murray Bridge SA and Mareeba QLD. Joe White Maltings, the CBH-owned malting operation, supplies the brewing sector with the largest malt house network in Australia. Cargill Animal Nutrition Australia operates several positions. BEC Feed Solutions, owned by the Bartholomeusz family, operates the largest Queensland independent. The Stockfeed Manufacturers Council of Australia (SMCA) sets the quality assurance and registration framework, the Department of Agriculture sets the animal feed regulatory framework, and AS 5812 covers the manufacture and supply of feed. A typical Australian stockfeed mill operates a 100 to 400 tonne per day pellet line with batching, mixing, pelletising, cooling, sieving and bagging, with dedicated premix and medicated feed circuits where cross-contamination control is critical.

Tier 4 — Oilseed crushing and animal protein rendering

Oilseed crushing in Australia is concentrated around canola and the smaller cottonseed and soybean streams. Cargill Footscray runs the largest single oilseed crushing operation. Riverina Oils & Bio Energy and others operate the broader oilseed crushing positions. Solvent extraction with n-hexane drives the AS/NZS 60079.10.1 Zone 1 hazardous area envelope around the extractor, desolventiser-toaster and condenser train. The animal protein rendering sector is the parallel by-product handler converting abattoir offal, hides, feathers, bone and blood into tallow, meat-and-bone meal, blood meal and feather meal. Tallowman Australia operates multiple sites. Mort & Co operates the Logan QLD rendering. AME Australian Meat and Edibles runs the major byproduct rendering line. The Australian Renderers Association (ARA) sets the industry framework. The HVAC challenge is dominated by odour at parts-per-billion thresholds, hot cooker non-condensable gases at 95 to 110 degrees C, evaporator overhead vapour streams, ammonia from the chiller engine room under AS 4332, and the air-quality interface with neighbouring communities.

Tier 5 — Pet food extrusion and pasta manufacturing

The Australian pet food industry has grown to a multi-billion dollar export sector dominated by extrusion-based dry kibble. Mars Petcare operates major sites at Wodonga VIC and Bathurst NSW producing the Pedigree, Whiskas, Optimum, Advance and Cesar brands. Nestlé Purina PetCare operates at Blayney NSW producing the Purina, Fancy Feast, Pro Plan and Felix brands. Real Pet Food Company, recently acquired by KKR private equity, operates at Ingleburn NSW producing the Pure Pets, Coopers, Black Hawk and Nature's Goodness brands. VIP Petfoods operates at Lyndon VIC. Hill's Pet Nutrition, the Colgate-Palmolive prescription pet nutrition brand, operates a smaller Australian footprint with most product imported. The Pet Food Industry Association of Australia (PFIAA) sets the industry framework. The HVAC challenge is dominated by the extruder die plate releasing superheated steam at 130 to 160 degrees C mixed with rendered fat aerosol, the post-extrusion fat-coating drum atomising tallow or chicken fat onto the kibble at 60 to 80 degrees C, the drying tunnel exhaust at 110 to 130 degrees C with combustion products from gas burners, and the kibble cooler exhaust managing fines and odour.

Adjacent to the pet food extruders sit the human-food pasta and rice operations. Capello Pasta operates the major VIC pasta extrusion position. San Remo Macaroni, owned by Cargill, operates the SA pasta production. SunRice (ASX:SGLN) operates the Leeton NSW rice mill that is the largest single rice handler in the southern hemisphere. The Pasta Manufacturers Association of Australia covers the broader category. Pasta extrusion driven HVAC differs from pet food only in the food contact rules (FSANZ rather than PFIAA), the absence of fat aerosol, and the much lower extruder die temperature.

Tier 6 — Adjacent grain-derived sectors

The broader grain ecosystem includes the malting sector for brewing and distilling (Joe White Maltings, Barrett Burston), the rice milling sector (SunRice Leeton), the bakery industry which is covered in the dedicated bakery and bread manufacturing HVAC duct guide, the sugar industry covered in the sugar mill, refinery, bagasse cogeneration, ethanol distillery and food-grade sugar packing HVAC duct guide, and the export grain terminal interface with the broader port and stevedoring sector covered in the container port, cargo terminal, stevedore and ferry HVAC duct guide.

The regulatory stack — what you have to comply with

Australian grain, flour, feed and pet food HVAC sits under a deeply layered regulatory stack. Each layer applies independently. Compliance with one does not waive any of the others.

AS 1668.2 — Mechanical ventilation in buildings

AS 1668.2 is the controlling Australian standard for mechanical ventilation. It specifies the minimum outdoor air rates, the calculation method for exhaust hoods, the safe discharge of exhaust to atmosphere, the spacing between exhaust and intake terminals, and the smoke control overlay. For grain, flour and feed sites it drives the supply air volume to each room, the makeup air volume that balances the dust extraction systems, the dispersal modelling for dryer and pellet cooler exhausts, and the AS 1668.2 hood capture velocity calculations for every dust generation source.

AS 4254 — Ductwork for air-handling systems in buildings

The duct itself, regardless of what flows through it, is fabricated to AS/NZS 4254. Part 1 covers flexible duct and Part 2 covers rigid duct. The standard specifies gauge, joint construction, support spacing, leakage class, pressure class and insulation. SBKJ fabricates all grain, flour, feed and pet food ducting to AS 4254 Class B leakage minimum, with Class A on food-grade and dust-extract circuits, and with the pressure class set to match the actual operating duty — typically 500 Pa for general supply and return, 1000 Pa for primary dust extract and 1500 Pa for high-velocity pneumatic conveying envelope ducts.

AS 1530.4 — Fire-resistance tests for elements of construction

AS 1530.4 governs the fire-rating of any duct penetrating a fire-rated wall or floor, plus the construction of fire-rated duct systems where the duct itself forms part of the fire compartment boundary. For grain, flour and feed sites the practical implication is that the silo battery, the elevator tower, the milling floor and the dust collector array are typically separate fire compartments and any duct connecting them carries an AS 1530.4 fire-rated damper at the boundary. AS 1851 covers the routine inspection and maintenance of those dampers.

AS 3957 — Dust hazard classification

AS 3957 is the Australian dust hazard classification reference. It cross-references the global NFPA framework and gives the practical guidance on dust hazard analysis methodology. For grain, flour and feed sites it is the document the dust hazard consultant works from to classify each location into the AS/NZS 60079.10.2 dust zone framework.

NFPA 660 — Standard for combustible dust

NFPA 660 is the 2025 consolidation of NFPA 484 (combustible metals), NFPA 654 (combustible particulate solids), NFPA 655 (sulphur), NFPA 61 (agricultural and food processing facilities) and NFPA 664 (wood processing). It is the governing global combustible dust standard and it explicitly covers grain dust, flour dust, bran dust, oilseed meal dust, feed dust and pet food kibble fines. The standard mandates a documented Dust Hazard Analysis for every dust generation, transport and collection point, conductive bonded ductwork, isolation between the dust collector and the upstream process, explosion venting or chemical suppression on the collector, and a documented housekeeping protocol with the well-known 3 millimetre maximum dust thickness limit on horizontal surfaces.

NFPA 68 — Explosion venting and NFPA 69 — Explosion prevention

NFPA 68 is the standard for explosion venting by deflagration. It gives the calculation methodology for sizing vent panels on dust collectors, silos, conveying envelopes and any other enclosed volume that could host a deflagration. Vent sizing depends on the dust Kst, the MEC, the enclosure volume, the enclosure strength (Pred), and the panel opening pressure (Pstat). NFPA 69 is the parallel standard for explosion prevention through inerting, oxidant concentration reduction, ignition source removal and chemical or mechanical isolation between connected enclosures. Both standards apply in full to every Australian grain elevator, flour mill, stockfeed pellet line and pet food kibble extruder line.

AS/NZS 60079 — Hazardous area classification

The AS/NZS 60079 series covers hazardous area classification for both flammable gas and combustible dust atmospheres. AS/NZS 60079.10.1 classifies gas zones (Zone 0, 1, 2) and applies to the hexane envelope around solvent extraction at oilseed crushers, the phosphine envelope around silo fumigation cycles, and the ammonia envelope around chiller engine rooms. AS/NZS 60079.10.2 classifies dust zones (Zone 20, 21, 22) and applies to every silo headspace, elevator leg, transfer chute, sifter, purifier, roller mill, pellet cooler, kibble extruder and dust collector enclosure. The classification determines the IECEx Ex rating of every motor, light fitting, sensor, instrument, damper actuator and ducting bond in the affected zone.

AS 1940 — The storage and handling of flammable and combustible liquids

AS 1940 governs the storage and handling of flammable and combustible liquids including n-hexane for solvent extraction, ethanol for adjacent operations and bulk diesel for grain dryers. It drives the bunding, ventilation, separation distance and hazardous area classification around fuel and solvent tank farms at oilseed crushers, ethanol distilleries adjacent to grain operations, and the fuel storage at silo and pellet mill sites.

AS 4036 and AS 4037 — Boiler and pressure equipment

AS 4036 covers boiler standards and AS 4037 covers pressure equipment. Both apply to the boilers used in grain drying (steam-assisted dryers), flour mill conditioning (temper-water heating), pellet mill steam injection (pre-conditioning the feed mash before the die), pet food preconditioning (steam injection at the extruder pre-cook), rendering cookers (live steam direct injection at 100 to 110 degrees C), and the rendering plant boilers themselves. The HVAC implication is that the boiler combustion air supply duct, the flue gas exhaust duct and the boiler room ventilation are all in the AS 4036 envelope and require AS 1668.2 compliant outdoor air, AS 1851 compliant dampers and AS 4254 compliant fabrication.

AS 1716 — Respiratory protective devices

AS 1716 governs respiratory protection. It applies to personnel entering fumigated silos, entering rendering raw-material bays, entering soybean extraction unit access points and any space where the airborne contaminant exceeds the WES. The HVAC implication is the design of the breathing-zone air supply system around the access door, the lockout integration with the silo aeration ducting, and the routing of self-contained breathing apparatus charging stations.

AS 4332 — The storage and handling of gases in cylinders and pressure vessels (ammonia chillers)

AS 4332 governs the storage and handling of compressed gases including the ammonia (NH3) used in industrial refrigeration at rendering plants, pet food cold storage, meat-protein cold rooms and finished tallow chillers. The HVAC implication is the design of the ammonia engine room ventilation under AS 4332, with continuous purge ventilation, 25 ppm ammonia alarm threshold, 150 ppm emergency evacuation, gas-tight isolation, intrinsically safe sensors, IECEx Ex e or Ex d motors and an emergency dump vent routed clear of occupied buildings.

AS 1851 — Routine service of fire protection systems and equipment

AS 1851 covers the routine inspection, testing and maintenance of fire protection systems including fire dampers, smoke dampers and fire-rated duct penetrations. For grain, flour and feed sites it drives the inspection schedule on every fire damper at the silo battery, elevator tower, mill compartment, dust collector enclosure and finished goods warehouse interface.

AS 1657 — Fixed platforms, walkways, stairways and ladders

AS 1657 governs platform and access design. It applies to the silo roof platform where dust collectors are mounted, the elevator tower head platform where bucket discharge spouts are accessed, the mill floor cleanout access platforms and the duct cleanout access at every 6 to 8 metres of straight run. The HVAC implication is that the duct cleanouts must be reachable from a compliant access platform — meaning the platform geometry is part of the duct design package, not an afterthought.

AS 1318 — Industrial chimneys

AS 1318 is the Australian standard for the construction of industrial chimneys. It applies to the discharge stack from a grain dryer combustion train, the discharge stack from a rendering plant odour control train, the discharge stack from a pet food drying tunnel exhaust and the discharge stack from any oilseed crushing solvent recovery train. Stack height, wall construction, lining, monitoring port and grounded conductor all flow from AS 1318.

FSANZ Food Standards Code 1.2.2 and 3.2.3

The FSANZ Food Standards Code is the binding regulation for all human-food production. Chapter 1.2.2 covers labelling and provenance. Chapter 3.2.3 covers food premises and equipment, and it interlocks with AS 4674. For flour mills, pasta plants and the human-food side of the sector, the relevant clauses concern positive pressure in clean zones, prevention of condensation drip from cold ducts onto product, separation of high-risk and low-risk areas, and cleanability and inspectability of all overhead ductwork. It is the document a food safety auditor will quote when inspecting a flour mill.

AS 5812 — Manufacture and supply of stockfeed

AS 5812 is the Australian standard for the manufacture and supply of stockfeed. It covers raw material sourcing, batching accuracy, mixer uniformity, pellet quality, medicated feed cross-contamination control, finished feed sampling and traceability. From an HVAC standpoint it drives the segregation of premix, medicated feed and finished feed ducting circuits where antibiotic, coccidiostat, vitamin and mineral cross-contamination must be physically prevented. The Stockfeed Manufacturers Council of Australia (SMCA) Quality Assurance scheme builds on AS 5812 with industry-specific audit overlay.

HACCP and ISO 22000

The Hazard Analysis and Critical Control Points framework and the parallel ISO 22000 food safety management system apply to every Australian flour mill and pet food extrusion plant supplying the major retail customers. The HVAC implications are documented airborne hazard identification (mould spores, dust, condensation, mycotoxins, foreign-body contamination from filter degradation), control specification (filter classes, differential pressure regime, inspection access), monitoring (continuous logging on temperature, humidity and pressure), and record-keeping (the full as-built and operational documentation pack).

ASHRAE Applications — Chapter 35 industrial drying and Chapter 27 process heat recovery

The ASHRAE Applications Handbook chapters on industrial drying and process heat recovery cover the calculation methodology for grain dryer thermodynamics, the moisture-extraction air handler for flour conditioning, the pellet mill cooler air flow versus pellet temperature target and the pet food drying tunnel energy budget. SBKJ engineers use ASHRAE Applications Ch 35 as the design reference for the dryer and cooler thermodynamics on every grain and feed project.

AS 4801 and the Department of Agriculture animal feed regulations

AS 4801 is the legacy Australian occupational health and safety management standard (now broadly aligned with ISO 45001). It applies to every grain handling and feed manufacturing site as the OHS framework. The Department of Agriculture animal feed regulations cover the registration of premixes, medicated feeds and the ingredient-specific restrictions on cross-contamination. Aboriginal Heritage protection regulations apply on any greenfield silo or terminal expansion in the affected zones — engagement with traditional owners is part of the project approvals envelope.

The grain-to-feed-to-pet-food process — and the HVAC zones that result

A working grain handling, flour milling, stockfeed manufacturing, rendering or pet food extrusion site is best understood as a process line rather than a building. Raw grain or raw material enters at one end and finished bagged product leaves at the other, with each intermediate stage demanding a different air condition. Below we walk the process and specify the ductwork for each zone.

Zone A — Grain receival, truck dump and primary cleaning

Grain arrives at an Australian country silo or export terminal by truck at peak harvest rates of 1,000-plus trucks per day across the November to January window. Each truck reverses over a grated dump pit, lifts the rear bin and pours 30 to 50 tonnes of harvest-fresh grain into the pit grate. The dump event releases a visible dust cloud as the grain falls onto the pit floor and is conveyed into the elevator leg boot. Dust concentration immediately above the grate exceeds the minimum explosible concentration during the few seconds of unloading, which is why the dump pit is the historically highest-frequency ignition location in the global grain elevator industry.

The HVAC duty at the receival is dominated by capture velocity. The dust extract hood above the dump grate has to draw at 0.5 to 1.5 metres per second face velocity across the open grate area, with sufficient volume to entrain the visible dust cloud during the active unloading second. Typical receival shed extract volumes run 30,000 to 80,000 cubic metres per hour depending on the truck throughput peak. The extracted air is conveyed through conductive bonded ducting to a primary cyclone separator (recovering the coarse grain dust and broken kernels as a valuable by-product) and then to a secondary bag filter with NFPA 68 explosion venting. The discharge fan must be a spark-resistant AMCA Type B or Type C centrifugal with aluminium impeller in a steel housing, located downstream of the bag filter and isolated from the extract trunk by a rotary airlock or a fast-acting chemical isolator.

The receival shed itself requires general displacement ventilation at 6 to 12 air changes per hour during peak harvest, sized to dilute residual airborne dust below the Safe Work Australia grain dust WES of 4 mg per cubic metre inhalable, plus the respirable crystalline silica WES of 0.05 mg per cubic metre (silica is present in field-soil contamination of the harvest grain), plus the endotoxin and fungal spore loading from the field. Personnel in the unloading bay wear AS 1716 compliant P2 or P3 respirators during active unloading events.

SBKJ supplies the receival ducting in two configurations. For straight runs and trunks, SBTF-1602 round spiral duct in conductive carbon steel or galvanised G300 is the standard product. Round geometry minimises dust accumulation on flat ledges, the spiral lockseam gives an inherent Class A leakage rate (under 0.5 percent at design pressure) which keeps capture velocity at the source rather than losing it to leakage, and the conductive metallic construction can be bonded and earthed continuously without a return path through the building structure. For very large primary trunks where the diameter exceeds the SBTF-1602 capacity, the SBTF-2020 large-diameter spiral tubeformer supplies up to 2000 mm diameter trunks in a single piece. For branch tap-offs and fitting work, the SBPC1500 plasma cutter cuts the fabricated rectangular and round transitions from sheet stock, the SBFB-1500 spiral fitting former produces matched spiral fittings, and the SBLR-600 laser welder joins the food-grade segments where applicable.

Zone B — Grain elevator leg and transfer points

The grain elevator leg is the vertical bucket conveyor that lifts the grain from the receival pit boot to the top of the silo headhouse for distribution into the storage cells. Australian elevator legs typically run 30 to 50 metres tall with a head pulley diameter of 600 to 1200 mm and a bucket discharge velocity at the head of 2 to 4 metres per second. The leg interior carries a continuous airborne dust cloud during operation and the head and boot bearings are the primary historical ignition sources in the global grain elevator industry — the General Foods Banks Mill explosion in 1981, the DeBruce explosion in 1998 and dozens of smaller events recorded by US OSHA and the Australian state regulators trace back to bearing failures, belt slippage, foreign objects in the cup train, or static discharge from accumulated dust on ungrounded internal surfaces.

The HVAC duty around the elevator leg is dust extract at the head pulley discharge (where the dust cloud is densest because the bucket is throwing grain over the head pulley into the discharge chute) and at every transfer point in the conveying train (silo discharge spout to receival belt, receival belt to elevator boot, elevator head to distribution chute, distribution chute to silo cell loading spout, silo discharge gate to ship-loader belt or truck loading hopper). Each capture point uses a localised hood with a face velocity of 0.5 to 1.0 metres per second drawing into conductive bonded duct.

The elevator leg itself is fitted with NFPA 68 explosion vents on the casing — typically at the head, at the boot and at intervals along the leg length — sized for the dust Kst and the casing strength. NFPA 69 fast-acting isolation valves go between the elevator leg and the silo cells, and between the elevator leg and the receival circuit, to stop a deflagration in the leg from propagating into the silo battery or back to the receival shed. Spark detection plus infrared spark-out injection upstream of every dust collector closes the loop. The bearing temperature monitoring (typically thermocouple plus vibration on every head and boot bearing) plus belt slip detection plus cup-train misalignment detection feeds back through the SCADA to automated shutdown.

SBKJ supplies the dust extract trunks from each transfer point as SBTF-1602 round spiral in conductive carbon steel, sized for the capture air volume plus a 20 percent margin for fugitive air ingress at the hood. The main collection trunk to the centralised bag filter is typically SBTF-1602 600 to 1000 mm diameter, with branch lines at 200 to 400 mm diameter and tap-off entry angles of 30 to 45 degrees to maintain transport velocity. Conveying velocity in the trunk is held at 18 to 22 metres per second — high enough to keep settled dust in suspension, low enough to avoid abrasive wear on the trunk wall.

Zone C — Silo storage, aeration and headspace ventilation

Australian grain silos hold 5,000 to 50,000 tonnes per cell at country positions and 20,000 to 60,000 tonnes per cell at port terminals. Construction is either galvanised steel (welded-sheet construction at 8 to 20 metres diameter) or concrete (slipformed at 15 to 25 metres diameter). Both construction types share the same HVAC envelope: forced aeration at 0.5 to 2 litres per second per stored tonne for insect and mould control, fumigation isolation for the phosphine treatment cycle, NFPA 68 explosion venting on the silo roof and side walls sized against the enclosure strength, and AS/NZS 60079.10.2 Zone 21 classification inside the silo headspace.

The aeration plenum is a network of perforated floor ducts or perforated lateral pipes laid in the silo floor that distributes the aeration air across the grain cross-section. The aeration fan (typically a low-pressure axial or centrifugal sized for the 0.5 to 2 L/s/t target and pressure-rated for the grain depth back-pressure) pushes ambient or cooled air through the grain mass to remove insect and mould-respiration heat, suppress fungal growth, and gently equalise the temperature and moisture across the stored grain mass. The discharge from the silo top is typically a passive louvre or a powered roof extract fan rated for the same flow.

The phosphine fumigation cycle is the dominant non-aeration HVAC event. Aluminium phosphide or magnesium phosphide pellets (commercial products Pixarvin, Magtoxin, Quickphos and Gastoxin) are placed inside the sealed silo and react with ambient moisture to release phosphine (PH3) gas at headspace concentrations of 200 to 800 ppm over a 7 to 14 day exposure cycle. The Safe Work Australia 8-hour WES for phosphine is 0.3 ppm with a STEL of 1 ppm — meaning even very small leaks present an acute toxicity risk to personnel within metres of the silo wall. The HVAC implications are: aeration is locked out during fumigation hold, gas-tight isolation dampers seal every duct connecting the silo to the rest of the facility, breathing-zone PH3 monitors with audible and visual alarms are installed downwind of silo vents, post-fumigation forced ventilation is routed through a scrubber or thermal destruction unit before re-entry is permitted, full self-contained breathing apparatus (SCBA) per AS 1716 is mandatory for any entry team, and the fumigation event is logged in the site SCADA against the Department of Agriculture export grain quarantine treatment standards.

Spontaneous heating of damp or under-aerated grain is the parallel concern. A spike in stack temperature above 45 degrees C indicates trouble — either insect activity (Tribolium, Sitophilus, Rhyzopertha species), mould activity (Aspergillus, Fusarium, Penicillium species producing aflatoxin, ochratoxin and fumonisin mycotoxins), or thermal degradation. The HVAC response is increased aeration airflow drawn through the warm zone to a downstream baghouse and discharge stack, plus CO and CO2 monitoring inside the silo headspace (a CO rise above 50 ppm indicates smouldering combustion), plus infrared thermal imaging of the silo roof and side wall to map the heat distribution.

SBKJ supplies the silo top dust collector ducting as SBTF-1602 spiral in galvanised G300, with NFPA 68 vent panels integrated into the bag filter housing and a discharge oriented away from occupied buildings and access ways. The aeration plenum supply ducting is typically SBTF-1602 or SBFB-1500 spiral fitting on the connection to the inlet fan, with all bonding and earthing verified to less than 1 megohm at every joint per AS/NZS 60079.14.

Zone D — Grain dryer and conditioning

Harvest-fresh grain arrives at 14 to 22 percent moisture content depending on the season and the field-side handling. To store safely for the post-harvest year, the grain must be dried to 12 to 13 percent for wheat, 12 percent for canola, 13 to 14 percent for sorghum and 14 percent for barley. The drying step uses either a continuous-flow rotary dryer, a continuous-flow column dryer or a batch tower dryer, with the heat source typically a direct-fired gas burner (LPG or natural gas) or an indirect-fired thermal oil heater. Dryer exit air carries grain dust, water vapour, combustion products and trace organic compounds from the grain husk degradation at 60 to 80 degrees C.

The HVAC duty is the dryer exhaust trunk — sized for the dryer airflow (typically 30,000 to 150,000 cubic metres per hour for an Australian commercial dryer), the temperature (60 to 80 degrees C continuous, peaks to 110 degrees C on burner upset), the dust loading (grain dust at MEC-exceeding concentration through the trunk interior), and the AS/NZS 60079.10.2 Zone 21 classification on the trunk interior. Material is 316L stainless or heavy-gauge galvanised G300 trunk, with a primary cyclone separator (recovering the carryover dust as a valuable bran by-product) followed by a bag filter with NFPA 68 explosion venting. The bag filter outlet discharge to an AS 1318 compliant stack at an elevation cleared with the local EPA for downwind dispersal modelling.

The dryer combustion air supply is sized for the burner rated heat input plus excess air, typically 6,000 to 30,000 cubic metres per hour depending on burner size. The combustion air supply duct is galvanised G300 in the standard SBAL-V coil line product, with the AS 4036 boiler combustion air clearance and the AS 1668.2 outdoor air intake terminal located clear of any silo top discharge or vehicle exhaust source.

SBKJ supplies the dryer exhaust trunk as SBTF-1602 spiral in 316L stainless when the duty exceeds 90 degrees C continuous, or as SBAL-V coil-line galvanised when the duty is below 80 degrees C. The cyclone connection is a fabricated transition from the SBPC1500 plasma cutter. The bag filter inlet is a flanged connection with a gasketed seal and an explosion isolation valve immediately upstream.

Zone E — Flour mill roller floor, sifter floor and purifier floor

The flour mill is the heart of the human-food side of the sector. A modern Australian flour mill grinds 200 to 1,500 tonnes of wheat per day on a roller-mill, sifter and purifier train, producing white flour, wholemeal, baker's grade, biscuit grade, durum semolina for pasta, and the bran and pollard by-product streams. The mill building is typically four to six storeys tall, with the wheat tempering bins on the top floor, the roller-mill grinders on the middle floors, the sifters and purifiers on the upper floors (gravity flow from the grinders to the sifters), and the finished flour silos and pneumatic conveying take-off on the lower floors. The HVAC challenge is dominated by flour dust at higher concentration than any bakery, with NFPA 660 St-3 Kst above 200 across the whole grinding, sifting and purifying envelope.

Each roller-mill stand has a dedicated dust extract hood at the discharge spout, capturing the airborne flour fines released as the wheat is broken between the rollers. The capture velocity at the spout is 0.5 to 1.0 metres per second, drawing into conductive bonded duct sized for transport velocity 18 to 22 metres per second. Each sifter has a top-mounted vent connecting to the mill dust collection system — the sifter agitation generates a continuous internal airflow and the vent ensures the sifter interior runs at slight negative pressure to prevent fugitive flour escape into the mill floor. Each purifier has a parallel arrangement with the air-aspiration above the purifier sieve drawing into the collection system.

The pneumatic conveying system that moves the flour streams between mill levels is itself a dust extract system in reverse — the conveying air carries the flour from the discharge of each grinder, sifter and purifier to the take-off cyclone at the finished flour silo. Conveying velocity is held at 22 to 28 metres per second to keep the flour in suspension without abrasive wear on the trunk wall. The take-off cyclone delivers the flour to the silo and the carrier air is filtered through a bag filter with NFPA 68 explosion venting before discharge.

The mill basement holds the centralised dust collection system — a battery of bag filters or cartridge filters sized for the total mill airflow (typically 100,000 to 400,000 cubic metres per hour for an Australian commercial mill), each filter unit fitted with NFPA 68 explosion vent panels sized against the housing strength, NFPA 69 fast-acting chemical or mechanical isolation valves on every inlet branch, spark detection plus infrared spark-out injection upstream of every filter, conductive bonded ducting throughout, and a documented housekeeping protocol with the 3 millimetre maximum dust thickness limit on horizontal surfaces. Spark-resistant centrifugal fans (AMCA Type B or C aluminium impeller in steel housing) handle the filtered air on the clean side.

Material selection is the single biggest fabrication decision in the mill. For the dust extract and conveying ducts, conductive carbon steel or 304 stainless is standard. For the food-contact zones — the finished flour silo air, the packing hall supply, the booth filling and bagging supply — 304L stainless is mandatory under AS 4674 and FSANZ 3.2.3 with continuous welded seams using the SBKJ SBSF-1525 stitchwelder plus the SB-ZF1500 longitudinal seam welder, internal grinding to Ra 0.8 micrometre or better, crevice-free TDF or flanged joints sealed with FDA-listed gasketing, and food-grade weld passivation. The mill packing hall typically holds 20 to 24 degrees C with HEPA-grade supply (H13 or H14 under EN 1822) downstream of the supply fan, positive pressure 10 to 15 pascals relative to surrounding zones, and continuous monitoring on differential pressure with alarm if drift outside the band exceeds 5 minutes.

SBKJ supplies the flour mill ducting as a mixed package. The dust extract trunks are SBTF-1602 spiral in conductive carbon steel for general use or 304 stainless for food-contact zones. The pneumatic conveying envelope ducts are SBTF-2020 large-diameter spiral where the throughput requires it. The food-grade plenum ducts in the packing hall and silo top supply are SBSF-1525 stitchwelder fabricated 304L stainless with the SB-ZF1500 longitudinal weld giving the continuous food-grade joint. Fittings, transitions and reducers are SBPC1500 plasma-cut and SBFB-1500 spiral-formed. Field welds are SBLR-600 laser welded where the AS 4674 surface finish requirement applies.

Zone F — Flour packing line and bulk container fill

The flour packing line takes finished flour from the silo and bags it into 25 kg, 10 kg, 5 kg and 1 kg consumer bags, plus 500 to 1500 kg bulk containers for the bakery and food service trade. Each bag fill nozzle is a primary dust generation source — the bag is presented to the spout, the spout opens, the flour drops into the bag at 50 to 200 kg per minute fill rate, the bag closes, the conveyor moves it on. During each fill event a visible flour cloud puffs out around the nozzle.

The HVAC duty is dust capture at every fill nozzle, with a localised hood drawing at 0.5 to 1.0 metres per second face velocity into the centralised dust collection system. The packing hall itself is held at 20 to 24 degrees C and relative humidity below 60 percent (flour deliquesces above 70 percent), with HEPA-grade supply downstream of the supply fan, positive pressure 10 to 15 pascals relative to surrounding zones, and AS 4674 compliant 304L stainless duct above all open product. Bulk container fill (500 to 1500 kg flexible intermediate bulk containers, FIBCs) operates with a sealed connection between the silo discharge spout and the container inlet, reducing the dust capture demand at the fill station but increasing the demand on the silo discharge connection.

The packing hall dust capture connects to the same centralised collection system as the mill floor, with NFPA 68 explosion venting and NFPA 69 isolation as required. Spark detection upstream of the collector is mandatory. The collected flour fines are recycled into a designated rework stream (the "screenings" or "rework" flour) rather than discarded, which adds value but also creates a microbial contamination risk if the rework is not handled hygienically.

Zone G — Bran, pollard and by-product handling

Wheat bran and pollard are the major by-products of the flour milling operation, separated from the white flour stream in the sifters and purifiers. They flow into the animal feed sector as the high-fibre raw material for stockfeed pellet manufacture. The HVAC duty is dust capture at the bran and pollard discharge spouts, the by-product conveying line, the by-product silo loading top, and the by-product loadout to truck or container. Bran dust shares the same NFPA 660 St-2 to St-3 explosion class as the parent flour, so all controls apply — conductive bonded duct, NFPA 68 explosion venting, NFPA 69 isolation, spark detection, spark-resistant fans.

SBKJ supplies the bran handling ducting as SBTF-1602 spiral in galvanised or conductive carbon steel, sized for the bran throughput and transport velocity at 22 to 28 metres per second. The by-product silo top dust collector follows the same configuration as the flour silo top, with NFPA 68 vent panels and bonded conductive construction.

Zone H — Pasta extrusion (durum semolina pasta)

The pasta extrusion line at Capello, San Remo and the regional pasta operations takes durum semolina from the flour mill, mixes it with water at a controlled ratio, extrudes the dough through a brass or PTFE-lined die at high pressure, and feeds the formed pasta into the drying tunnel. The extruder die plate is typically at 40 to 60 degrees C during operation, much cooler than the pet food extruder. The drying tunnel holds the pasta at 50 to 90 degrees C for several hours (depending on the pasta shape and the drying programme) at controlled humidity to drive the moisture from 30 percent post-extrusion to 12 to 13 percent finished.

The HVAC duty is the drying tunnel exhaust trunk and the drying tunnel supply trunk. The supply trunk is heated and humidified air from a dedicated air handler. The exhaust trunk carries the moisture-laden air at 50 to 90 degrees C from the tunnel back to a heat-recovery exchanger and partial outdoor discharge. Material is 304L stainless throughout the food-contact envelope under FSANZ 3.2.3, with continuous welded seams and internal grinding to Ra 0.8 micrometre or better.

SBKJ supplies the pasta drying tunnel supply and exhaust as SBSF-1525 stitchwelder fabricated 304L stainless with the SB-ZF1500 longitudinal seam welder. The trunk is externally insulated with rockwool 50 mm and a stainless skin to control thermal loss and surface condensation in the surrounding factory space.

Zone I — Stockfeed batching, mixing and pellet line

The stockfeed mill at Ridley AgriProducts, BEC Feed Solutions, Cargill Animal Nutrition and the regional operators operates a sequence of batching, mixing, pelletising, cooling, sieving and bagging. Batching takes raw materials (grain, oilseed meal, animal protein meal, vitamin premix, mineral premix, fat, molasses and a long list of minor ingredients) from individual storage bins and delivers metered quantities to the mixer. Mixing blends the raw materials to a uniform mash. Pelletising forces the mash through a die at elevated temperature and pressure (typically 70 to 90 degrees C and 100 to 200 bar) to produce the finished pellet. Cooling brings the hot pellet from die exit at 80 to 90 degrees C down to ambient plus 5 to 10 degrees. Sieving separates the off-spec fines from the on-spec pellets. Bagging fills the finished pellets into 20 to 25 kg consumer bags or 500 to 1000 kg bulk containers.

The HVAC duty has multiple parts. The batching and mixing hall requires general displacement ventilation at 6 to 10 air changes per hour with dust capture at the mixer charging point. The pellet mill itself has steam injection at the pre-conditioner (a horizontal cylinder upstream of the die where the mash is steam-conditioned to 70 to 90 degrees C at 14 to 16 percent moisture) and the steam supply is an AS 4036 compliant boiler. The pellet cooler is the largest single HVAC duty in the stockfeed mill — ambient air drawn through the cooler bed at 1.0 to 1.5 cubic metres per minute per square metre of bed area, lifting the pellet temperature down from die exit and removing the surface moisture. The exhaust from the pellet cooler carries grain dust, fat aerosol from the molasses and rendered animal fat ingredients, and steam from the residual moisture release.

The pellet cooler exhaust trunk is conveyed through conductive bonded duct to a primary cyclone (recovering the coarse pellet fines for rework) followed by a bag filter or scrubber. Material is 304L stainless for the food-grade circuit (where AS 5812 applies) or galvanised G300 for the non-food-grade circuit. The bagging line operates with localised dust capture at every fill nozzle and a separate dust collection circuit serving the bagging hall.

The premix and medicated feed circuits require physically segregated ducting under AS 5812 to prevent cross-contamination of antibiotic, coccidiostat, vitamin and mineral residues between batches. The Stockfeed Manufacturers Council of Australia (SMCA) Quality Assurance scheme and the Department of Agriculture animal feed regulations both require documented HVAC segregation. SBKJ supplies the premix and medicated circuits as physically separate duct runs in 304L stainless with their own dedicated dust collectors, dedicated exhaust fans and dedicated maintenance and cleaning protocols.

SBKJ supplies the stockfeed mill ducting as SBTF-1602 and SBTF-2020 spiral in galvanised G300 for the main batching, mixing and cooler trunks, transitioning to SBSF-1525 stitchwelder fabricated 304L stainless for the premix, medicated and food-grade circuits. Fittings and transitions are SBPC1500 plasma-cut and SBFB-1500 spiral-formed. Field welds on the food-grade circuit are SBLR-600 laser welded for AS 4674 surface finish.

Zone J — Oilseed crushing and solvent extraction

Oilseed crushing at Cargill Footscray, Riverina Oils & Bio Energy and the regional operations takes canola, soybean and cottonseed and produces vegetable oil and the protein-rich meal residue. Mechanical pressing is the first stage — the seed is preheated, cracked, flaked and pressed at high pressure to release the bulk of the oil. Solvent extraction is the second stage — the press cake is contacted with n-hexane in a counter-current extractor to recover the residual oil, then the meal is desolventised in a steam-heated toaster vessel to drive off the hexane.

The HVAC challenge is dominated by n-hexane as a Class 1 Group D flammable liquid under AS 1940. The LEL for hexane is 1.1 percent v/v in air, the flashpoint is minus 26 degrees C, and the Safe Work Australia 8-hour WES is 50 ppm with a STEL of 125 ppm. The extractor vessel is internally Zone 0 under AS/NZS 60079.10.1. The desolventiser-toaster shell, the mineral oil scrubber and the condenser train are typically Zone 1. The broader extraction building is Zone 2 provided forced ventilation maintains the ambient hexane vapour concentration below 25 percent of LEL.

HVAC equipment inside Zone 1 must use Ex d or Ex e motors, intrinsically safe instruments, bonded conductive ductwork verified less than 1 megohm to earth at every joint per AS/NZS 60079.14, intrinsically safe damper actuators, and a documented hazardous area dossier authored by a competent person. Building ventilation is sized for 12 to 20 air changes per hour to maintain the dilution envelope, with the supply intake located clear of any hexane vent or transfer point and the building exhaust routed through a vapour recovery condenser before discharge.

SBKJ supplies the extraction building HVAC as 316L stainless on the hexane-exposed segments and galvanised G300 on the non-exposed segments. All bonding is verified at commissioning and re-verified at the annual hazardous area dossier review.

Zone K — Vegetable oil refining

Crude vegetable oil from the oilseed crushing operation passes through a refining train: degumming (removal of phospholipids), neutralisation (caustic refining to remove free fatty acids), bleaching (decolourisation through activated bleaching earth), and deodorising (vacuum stripping at 240 to 270 degrees C to remove residual volatile compounds). Each stage carries its own HVAC duty.

The deodoriser is the highest-temperature unit — a vacuum vessel held at 2 to 6 mbar absolute with the oil heated to 240 to 270 degrees C. Steam stripping pulls the volatile compounds into the vacuum, where they are condensed and recovered as a fatty acid distillate. The vacuum system exhaust carries the residual non-condensable gases plus trace fatty acid aerosol at low temperature. Material is 316L stainless for the deodoriser shell and immediate downstream piping. The boiler that generates the deodoriser stripping steam is AS 4036 compliant. The bleaching earth handling is a fine-dust system requiring conductive bonded duct and NFPA 68 explosion venting on the bleaching earth handling silo and the spent earth filter.

Zone L — Rendering plant raw bay, cooker, evaporator and odour control

The rendering plant at Tallowman Australia, Mort & Co, AME Australian Meat and Edibles and the captive renderers within the major meat works (JBS, Teys, Australian Country Choice, Northern Cooperative Meat) processes abattoir offal, hides, feathers, bone and blood into tallow, meat-and-bone meal, blood meal and feather meal. The HVAC challenge is dominated by odour at parts-per-billion thresholds, with reduced sulphur compounds (hydrogen sulphide, mercaptans), nitrogen-bearing compounds (trimethylamine, ammonia), short-chain aldehydes and ketones all present in the cooker non-condensable gas (NCG) stream, the evaporator overhead vapour, the raw material reception bay air and the finished tallow load-out vapour.

The HVAC duty is two-stage odour control. High-strength NCG and evaporator overhead vapour are routed through a regenerative thermal oxidiser (RTO) at 800 to 850 degrees C residence time 0.75 to 1.0 second, with 316L stainless or refractory-lined inlet ducting (no carbon steel because of sulphur acid attack on cooldown). Low-strength building air from the raw bay, cooker hall, finished product warehouse and load-out interface is routed through a packed-bed wet scrubber with biological polishing or a biofilter, with 316L stainless or FRP inlet ducting.

The raw material reception bay is held at slight negative pressure (typically 10 to 25 pascals below adjacent zones) to contain the odour and prevent fugitive release into the surrounding factory and neighbourhood. The cooker hall is similarly held at slight negative pressure. The finished tallow tank vent is routed through a dedicated odour control circuit because tallow at storage temperature (50 to 60 degrees C) continues to release volatile odour compounds.

The ammonia chiller engine room serving the rendering plant cold storage is governed by AS 4332 with continuous purge ventilation, 25 ppm ammonia alarm, 150 ppm emergency evacuation, gas-tight isolation, intrinsically safe sensors, IECEx Ex e or Ex d motors and an emergency dump vent routed clear of occupied buildings.

The discharge stack from the RTO and from the scrubber/biofilter is AS 1318 compliant industrial chimney with continuous emissions monitoring per the relevant state EPA conditions. The Australian Renderers Association (ARA) sets the industry-specific best practice for odour management and emissions reporting.

Zone M — Pet food extrusion line

The pet food extrusion line at Mars Petcare Wodonga and Bathurst, Nestlé Purina Blayney, Real Pet Food Company Ingleburn, VIP Petfoods Lyndon and Hill's Pet Nutrition operates a sequence of dry ingredient batching, mixing, preconditioning, extrusion, drying, coating, cooling and bagging. The dry ingredients (grain, oilseed meal, animal protein meal, vitamins, minerals) are batched and mixed, then conveyed to the preconditioner. The preconditioner injects live steam to heat the mash to 90 to 100 degrees C at 25 to 30 percent moisture. The extruder takes the preconditioned mash, compresses it under high pressure through a die plate at 130 to 160 degrees C, and cuts the expanded kibble to size. The drying tunnel reduces the kibble moisture from 25 percent to 8 to 10 percent through 30 to 60 minutes of hot-air exposure at 110 to 130 degrees C. The coater drum atomises liquid tallow or chicken fat plus flavour and digest onto the kibble surface at 60 to 80 degrees C. The cooler brings the kibble down to ambient. The bagger fills the finished kibble into 1 to 20 kg consumer bags.

The HVAC challenge is dominated by the extruder die plate exhaust (superheated steam at 130 to 160 degrees C mixed with rendered fat aerosol), the drying tunnel exhaust (combustion products from gas burners plus moisture from the kibble at 110 to 130 degrees C), the coater drum vent (fat aerosol plus volatile flavour compounds), and the cooler exhaust (residual moisture plus kibble fines).

Material selection is driven by the fat aerosol. The extruder hood, drying tunnel exhaust, coater drum vent and cooler exhaust must be 316L stainless (not 304L) because animal fat acids attack the chromium passivation of 304L over months of exposure. The fat aerosol also coats the duct interior and creates a Class 2 grease duct condition under AS 1668.2 — meaning sloped duct at 1:25 minimum to grease drain plug, daily wash-down provision, inspection cleanouts every 3 metres, and an in-line fat aerosol mist eliminator before any abatement equipment.

Pet food kibble dust still tests Kst around 150 to 200 (St-2 to St-3) so NFPA 660 combustible dust controls apply to the kibble cooler exhaust, kibble coating drum vent, bagging line dust capture and finished bag-fill stations. Conductive bonded duct, NFPA 68 explosion venting, NFPA 69 isolation, spark detection and spark-resistant fans all apply.

The bagging hall is held at 20 to 24 degrees C and relative humidity below 60 percent (kibble absorbs moisture above 65 percent RH and the finished bag becomes soft). HEPA-grade supply air downstream of the supply fan plus positive pressure 10 to 15 pascals relative to surrounding zones plus continuous monitoring on differential pressure.

SBKJ supplies the pet food extruder line ducting as SBSF-1525 stitchwelder fabricated 316L stainless with the SB-ZF1500 longitudinal seam welder, externally insulated with rockwool 50 to 100 mm and a stainless skin. Fittings and transitions are SBPC1500 plasma-cut and SBFB-1500 spiral-formed. The food-grade weld passivation is part of the standard fabrication routine.

Zone N — Finished feed and pet food warehouse

The finished feed and pet food warehouse holds palletised product before despatch to the customer. The HVAC duty is conditioned dry storage at 20 to 24 degrees C and relative humidity below 65 percent. Pet food kibble in particular degrades rapidly if humidity rises above 70 percent — the surface fat oxidises, the bag becomes soft, the kibble texture drifts and the consumer-facing product fails on shelf. The warehouse therefore runs a dedicated air handler with active dehumidification and a controlled fresh air bleed for personnel comfort.

Zone O — QC laboratory, mycotoxin and protein testing

Every Australian flour mill, stockfeed mill, rendering plant and pet food plant operates an on-site QC laboratory for moisture, protein, mycotoxin (aflatoxin, ochratoxin, fumonisin, deoxynivalenol), pesticide residue and microbiological testing. The HVAC requirement is laboratory-grade fume hood extract for the wet chemistry bench, biological safety cabinet extract for the microbiology bench, and general laboratory ventilation at 8 to 12 air changes per hour with HEPA-grade supply.

Zone P — Office and amenity

The site office and amenity (locker room, mess hall, ablutions) operate under standard AS 1668.2 commercial ventilation rates with no special process consideration beyond the cross-contamination isolation from the production hall.

Materials — when galvanised is fine and when only stainless will do

Material selection in a grain, flour, feed, rendering and pet food site is more nuanced than a simple "stainless everywhere" rule. Stainless is more expensive, harder to fabricate, harder to insulate and not always necessary. The right material depends on zone classification, temperature, moisture, food contact, fat exposure and chloride loading.

Galvanised G300 (general non-food, non-fat, low-chloride duct)

Galvanised G300 in 0.8 to 1.5 mm gauge fabricated to AS 4254 on the SBKJ SBAL-V auto duct line is the standard product for the bulk of non-food-contact duct. Grain receival shed extract, elevator leg dust capture, silo aeration plenum supply, dryer exhaust below 80 degrees C, stockfeed batching and mixing extract, finished feed warehouse supply, pet food bagging hall return (not above open product), office and amenity HVAC all use galvanised. The advantage is cost (roughly 30 percent of stainless), fabrication speed (the SBAL-V lockseam closes cleanly and consistently), and weight (lighter than stainless of equivalent gauge, easier to handle and install). The Z275 or G300 coating is suitable for the moderate moisture loading of inland Australian sites and the non-aggressive dust loading of grain and feed environments.

304L stainless (food-contact human-food duct above product)

304L stainless (1.4307) is mandatory for all human-food contact duct above open product, all duct downstream of HEPA filters in flour mill packing halls, all duct in pasta drying tunnels, and the food-grade segments of stockfeed mill premix and medicated feed circuits where the AS 5812 segregation rules apply. Fabrication is on the SBKJ SBSF-1525 stitchwelder with the SB-ZF1500 longitudinal seam welder for continuous food-grade welds, internal grinding to Ra 0.8 micrometre or better, crevice-free TDF or flanged joints sealed with FDA-listed gasketing, and food-grade weld passivation. The grade is 304L rather than 316L for general food zones because chloride exposure is low at inland mill sites.

316L stainless (chloride-exposed, fat-exposed and high-temperature duct)

316L stainless (1.4404) is the upgrade specification for chloride-exposed positions (coastal Newcastle, Brisbane, Geelong, Port Adelaide, Kwinana, Albany mill exposure), fat-exposed positions (pet food extruder hood, drying tunnel exhaust, coater drum vent, cooler exhaust, rendering tallow load-out and storage vent), high-temperature positions (grain dryer exhaust above 90 degrees C continuous, pasta drying tunnel exhaust, oilseed deodoriser exhaust), and corrosive vapour positions (sulphitation SO2 in oilseed bleaching, hexane condenser train, rendering RTO upstream segment). The molybdenum content of 316L gives the chloride pitting resistance and the resistance to fat acid attack that 304L lacks. Fabrication uses the same SBKJ SBSF-1525 plus SB-ZF1500 toolset with the appropriate filler metal selection.

Conductive carbon steel (combustible dust extract trunks)

Conductive carbon steel painted with an electrically continuous internal coating is the standard for the combustible dust extract trunks where food-contact is not required but conductive bonding is mandatory under NFPA 660 and AS/NZS 60079.14. The trunk wall is electrically continuous to less than 1 megohm to earth at every joint, every flange and every change of direction. SBKJ supplies these as SBTF-1602 and SBTF-2020 spiral fabrications with welded joints and flanged interfaces.

Refractory-lined carbon steel (high-temperature rendering RTO and grain dryer)

Refractory-lined carbon steel is the standard for the high-temperature segments of the rendering RTO (800 to 850 degrees C residence chamber), the grain dryer combustion chamber (60 to 110 degrees C exhaust but with burner upset peaks much higher), and the AS 1318 industrial chimney stack interior where the discharge temperature exceeds 200 degrees C. SBKJ supplies these as fabricated heavy-plate components with internal ceramic fibre or refractory cast lining installed at the workshop and field-jointed on site with flanged connections.

Polypropylene and FRP (acid scrubber and biofilter)

Polypropylene and fibre-reinforced plastic (FRP) ducting is the standard for the rendering plant wet scrubber inlet and the biofilter inlet where the air stream is corrosive (sulphur compounds, ammonia, organic acids) and the temperature is below 60 degrees C. Polypropylene gives excellent corrosion resistance at moderate cost. FRP gives equivalent corrosion resistance plus higher temperature capability. Neither material is suitable for combustible dust extract because the wall is not conductive and cannot be bonded.

Acoustics — keeping a flour mill or pet food extruder under NC-60

Industrial grain, flour, feed, rendering and pet food sites are mechanically intensive. Roller-mill grinders, sifters, purifiers, pellet mill dies, extruders, hammer mills, fan banks, refrigeration compressors, packaging machines and conveyor drives all contribute to the noise floor. The HVAC ductwork itself can be a significant contributor if it is not designed for low velocity and well-attenuated transmission. SBKJ specifies grain and feed mill ducting for an in-room noise criterion of NC-60 (around 60 dBA) for the production hall, NC-50 (around 55 dBA) for the packing and bagging halls, and NC-40 (around 45 dBA) for the QC laboratory and the office and amenity zones.

The main acoustic strategies are velocity control (supply duct velocity below 7 metres per second in main trunks, below 4 metres per second within 5 metres of a diffuser in occupied zones), in-duct attenuators on each supply branch into a critical noise zone, vibration-isolated fan mountings on every air handler and dust collector fan, and flexible canvas connections between the fan and the rigid duct. The bagging halls additionally receive lined duct (perforated stainless with absorbing fill behind) in the final 3 to 6 metres of supply ducting before each diffuser. The QC laboratory and office zones use the standard SBKJ acoustic duct package described in the dedicated acoustic HVAC duct lining and attenuator guide.

The keystone case studies — what they teach us

Three global grain elevator and flour mill incidents have shaped Australian regulatory practice and SBKJ engineering specification more than any others. They are referenced in every flour mill HACCP, every grain elevator Process Hazard Analysis and every stockfeed mill insurance underwriting review.

General Foods Banks Mill, Cambridge MA, 1981

The General Foods flour and starch mill at Banks Mill in Cambridge, Massachusetts deflagrated in 1981 with multiple fatalities and substantial property loss. The investigation traced the initiating event to a static spark on an ungrounded section of pneumatic conveying duct, with the primary deflagration in the sifter floor and secondary deflagrations propagating through the dust collection system into the basement. The keystone lesson was the importance of continuous conductive bonding on every duct section, every flange and every transition, plus the criticality of isolation between the dust collector and the upstream process. The General Foods event is the standard global reference for NFPA 660 and AS/NZS 60079.14 bonding practice.

DeBruce Grain Elevator, Wichita KS, 1998

The DeBruce Grain elevator at Wichita, Kansas exploded in 1998 with seven fatalities and ten injuries. The investigation traced the initiating event to a hot bearing on an elevator leg head pulley, with the primary deflagration in the leg casing and secondary deflagrations propagating through the elevator tower and the silo battery. The keystone lessons were the importance of continuous bearing temperature monitoring with automated shutdown above the alarm threshold, the criticality of NFPA 68 explosion venting on the elevator leg casing at the head, boot and intervals along the length, and the value of NFPA 69 fast-acting isolation between the leg and the silo cells. Every Australian grain elevator built or rebuilt after 2000 follows the DeBruce lessons.

Imperial Sugar Refinery, Port Wentworth GA, 2008

The Imperial Sugar refinery at Port Wentworth, Georgia exploded in 2008 with 14 fatalities and 36 injuries. The investigation traced the initiating event to a confined dust cloud inside an enclosed packaging conveyor, with the primary deflagration igniting accumulated white sugar dust on the surrounding structure and triggering secondary deflagrations that propagated along the entire packaging line. The keystone lesson was the importance of housekeeping and the 3 millimetre maximum dust thickness limit on horizontal surfaces — the Imperial Sugar facility had decades of accumulated dust on beams, ledges and conduit runs, and the secondary explosions were fuelled by that accumulated dust rather than the airborne primary cloud. Every Australian flour mill, stockfeed mill and pet food plant audit since 2008 has explicitly checked the 3 millimetre rule across every horizontal surface in the facility.

The Australian harvest and the seasonal HVAC calendar

The Australian grain harvest runs late October through January in the southern states and earlier in the north, with the wheat harvest peaking in November and December across NSW, Victoria, South Australia and Western Australia. Sorghum and summer-cropped grains peak in March to May in northern New South Wales and Queensland. The seasonal HVAC calendar at a grain terminal therefore has three modes: pre-harvest preparation (August to October, with full inspection of every silo aeration plenum, every elevator leg dust extract, every dust collector, every NFPA 68 vent panel and every fumigation isolation damper), harvest peak operation (October to January, with continuous operation at maximum throughput and zero tolerance for downtime), and post-harvest carry-over storage (February to October, with active aeration, fumigation cycles every 3 to 6 months depending on the grain age and the insect monitoring result, and the slower seasonal turnover into export and domestic milling demand).

The flour mill seasonal calendar is more uniform because the wheat supply is buffered through the silo carry-over storage, but capital works and major maintenance still concentrate in the September to November window before the new-season wheat enters the mill stream. The stockfeed mill seasonal calendar follows the livestock production cycle — the peak demand for pelletised feed coincides with the dairy spring flush, the feedlot finishing windows and the broiler and layer poultry cycles. The pet food extrusion plant runs uniformly through the year with the only seasonal flex tied to the export shipping schedule into Asia.

SBKJ machine configuration for the grain-to-feed-to-pet-food sector

SBKJ supplies the fabricating machinery for grain, flour, feed, rendering and pet food ductwork from a coordinated machine catalogue. The full catalogue is at the SBKJ machine catalogue and the sector-specific configuration is summarised below. The SBAL-V flagship product page is at the SBAL-V auto coil duct line product page.

SBAL-V auto coil duct line — general galvanised supply, return and exhaust trunk fabrication

The SBAL-V is SBKJ's flagship auto duct production line. It feeds galvanised G300 or stainless 304L/316L coil, levels, decoils, slits, notches, beads, cleats, folds and produces complete rectangular duct sections in a single operation. For grain, flour, feed, rendering and pet food work, the machine is typically configured with the standard galvanised tooling for the bulk of the ducting in non-food, non-fat, low-chloride positions, and a quick-change stainless tooling set for the food-contact, fat-exposed and chloride-exposed positions. The galvanised stock is run on G300 coil, the stainless on 304L or 316L grade in 0.8 to 1.2 mm thickness for general ductwork or 1.5 to 2.0 mm for high-pressure exhaust trunks. Total throughput on a single shift exceeds 800 metres of finished duct, sufficient to supply a complete country silo HVAC retrofit in two to three days or a complete flour mill section in two to three weeks.

SBTF-1602 and SBTF-2020 spiral tubeformer — round trunks for dust extract and pneumatic conveying

The SBTF-1602 fabricates round spiral lockseam ducting in 250 to 1,600 mm diameter from galvanised, stainless or carbon steel strip stock. The SBTF-2020 extends the range to 2,000 mm diameter for the primary dust collection mains, the pneumatic conveying envelope ducts and the cyclone return trunks that exceed the SBTF-1602 capacity. For grain, flour, feed and pet food applications, round spiral is the preferred geometry for the dust extraction main runs, the silo aeration plenum, the dryer exhaust trunk, the pellet cooler exhaust trunk, the pet food extruder hood trunk and any trunk where leakage class is critical and dust accumulation on internal ledges must be minimised. The spiral lockseam achieves AS 4254 Class A leakage rates (under 0.5 percent at design pressure) inherently — no field caulking required. SBKJ ships the SBTF-1602 and SBTF-2020 with galvanised, stainless and carbon steel tooling included as standard, with field calibration during installation.

SBSF-1525 stitchwelder plus SB-ZF1500 longitudinal seam welder — food-grade stainless plenum

The SBSF-1525 stitchwelder and the SB-ZF1500 longitudinal seam welder are the SBKJ machines for food-grade stainless plenum and trunk fabrication. The SBSF-1525 stitchwelds the rectangular section corners and the SB-ZF1500 lays a continuous longitudinal seam weld along the length, giving the crevice-free food-grade joint required under AS 4674 and FSANZ 3.2.3. For flour mill packing halls, pasta drying tunnels, pet food bagging halls and the food-grade segments of stockfeed premix and medicated feed circuits, this is the standard fabrication route. Internal grinding to Ra 0.8 micrometre or better is part of the standard finishing sequence.

SBFB-1500 spiral fitting former — matched spiral fittings

The SBFB-1500 spiral fitting former produces matched spiral fittings — elbows, tees, reducers, transitions, branch tap-offs — in galvanised, stainless or carbon steel. For grain, flour, feed and pet food applications, the matched spiral fitting maintains the same internal smoothness and the same leakage class as the straight trunk, avoiding the dust accumulation and the leakage that fabricated rectangular fittings introduce. SBFB-1500 fittings ship as flanged or push-fit-with-clamp ready for field jointing.

SBPC1500 plasma cutter — fabricated transitions and hood blanks

The SBPC1500 plasma cutter cuts fabricated transitions, hood blanks, custom flanges and the project-specific sheet metal components that the coil-line and spiral former cannot produce from standard stock. For grain receival hood plates, elevator leg discharge transitions, pet food extruder hood frames and rendering plant odour collection plenum blanks, the SBPC1500 is the standard fabrication route. Cutting tolerance is plus or minus 0.5 mm with the standard plasma torch and finer with the high-definition option.

SBLR-600 laser welder — food-grade field welds and fine fabrication

The SBLR-600 laser welder is the SBKJ machine for fine fabrication welds where the AS 4674 surface finish requirement applies. For flour mill packing hall internal field welds, pasta drying tunnel internal field welds, pet food bagging hall internal field welds and the food-grade ducting tie-in welds where the inside of the duct must be smooth and crevice-free, the SBLR-600 produces a narrow heat-affected zone with minimal surface disturbance and minimal post-weld grinding. The food-grade weld passivation is applied immediately after welding to restore the chromium passivation layer.

Spark-resistant fans and explosion isolation devices — sourced from SBKJ partner network

Spark-resistant centrifugal fans (AMCA Type B or Type C with aluminium impeller in steel housing) and NFPA 69 explosion isolation devices (rotary airlocks, fast-acting chemical isolators, infrared spark detection plus water-mist or CO2 injection systems) are not SBKJ fabricated products but are specified and sourced through the SBKJ partner network for delivery as part of the project HVAC package. The SBKJ engineering team handles the specification, the procurement coordination, the integration with the SBKJ-fabricated ducting and the commissioning sign-off.

Commissioning and validation — what a grain, flour, feed or pet food HVAC sign-off looks like

An HVAC system serving a grain handling, flour milling, stockfeed manufacturing, rendering or pet food extrusion site is not commissioned in the traditional building-services sense of "balance the dampers and walk away." The validation is a multi-layered exercise that has to satisfy the dust hazard analysis, the hazardous area dossier, the food safety auditor, the AS 5812 stockfeed regulator, the PFIAA pet food framework, the ARA rendering odour audit, the relevant state EPA and the Department of Agriculture animal feed registration.

The commissioning sequence runs in six stages.

1. AS 4254 ductwork leakage test. Each main duct system tested at design pressure with a calibrated leakage tester. Class A on dust extract and food-grade circuits, Class B on general circuits.
2. Air volume balancing. Every diffuser, grille, hood and extract point measured against the design schedule, with adjustment at the dampers until every zone is within tolerance.
3. Hazardous area bonding verification. Every duct joint, flange and transition verified less than 1 megohm to earth per AS/NZS 60079.14, with the bonding survey log retained on the site file.
4. Dust hazard analysis walk-through. Joint inspection by the SBKJ commissioning engineer, the operator's safety team and an external dust hazard consultant against the NFPA 660 DHA worksheet, the 3 millimetre housekeeping check on every horizontal surface, the spark detection function test, the NFPA 68 vent panel inspection and the NFPA 69 isolation function test.
5. Environmental conditioning. Each zone held at design temperature, humidity and pressure differential for at least 24 hours under stable load, with calibrated dataloggers recording the result. Food-grade packing halls verified for HEPA filter integrity per AS 1807.
6. Regulatory and audit sign-off. FSANZ 3.2.3 walk-through for the flour mill packing and pasta plant. AS 5812 documentation pack for the stockfeed regulator. PFIAA documentation for the pet food plant. ARA review for the rendering plant. State EPA stack emissions verification. Department of Agriculture animal feed registration verification. AS 4332 ammonia engine room sign-off where applicable. AS 1716 respiratory programme verification where applicable.

The deliverable is an as-built documentation pack that includes the duct layout drawings, the AS 4254 leakage test certificates, the air balance report, the bonding survey log, the 24-hour environmental log, the DHA walk-through report, the regulatory sign-offs, the HACCP plan reference, the AS 5812 segregation register, the fumigation procedure (where applicable), the ammonia engine room procedure (where applicable), and the maintenance schedule with cleaning frequency for each duct section. This pack lives with the site safety and quality records and is reviewed at each annual audit cycle.

Maintenance — what changes the 10-year operating cost

HVAC maintenance in a grain, flour, feed, rendering or pet food site is heavier than in a comfort-cooling office. The dust loading, humidity exposure and combustion product exposure mean filters fill faster, ductwork accumulates film, NFPA 68 vent panels need annual inspection, NFPA 69 isolation devices need quarterly function testing, hazardous area bonding needs re-verification at every joint disturbance, and the housekeeping protocol needs daily attention to maintain the 3 millimetre dust thickness limit on horizontal surfaces.

Supply air filters in the production area are replaced every 1 to 3 months. HEPA final filters in the flour mill packing hall, the pasta plant and the pet food bagging hall are replaced every 12 to 24 months with integrity testing to AS 1807. Dust collector cartridges or bags are replaced every 6 to 12 months with pressure drop monitoring driving exact timing. Spark detection function tests are quarterly. NFPA 68 vent panel visual inspections are annual with replacement on any deformation. NFPA 69 isolation valve function tests are quarterly with replacement on any out-of-spec response time.

Rendering plant RTO ceramic media is replaced every 5 to 10 years depending on the duty cycle, with the inlet duct interior inspected at every media replacement. Rendering scrubber packing is replaced every 2 to 5 years. The biofilter media is replaced every 3 to 5 years.

Pet food extruder grease duct (the Class 2 grease duct under AS 1668.2 from the extruder hood, drying tunnel exhaust, coater drum vent and cooler exhaust) requires daily wash-down provision and inspection cleanouts every 3 metres. The grease drain plug must be checked at every shift change. The in-line fat aerosol mist eliminator before any abatement equipment requires monthly cleaning.

The maintenance schedule and the recommended cleaning frequency for each duct section is detailed in the dedicated HVAC duct machinery maintenance schedule guide.

Lead time and SBKJ delivery for an Australian grain-to-pet-food project

For an SBAL-V auto coil duct line in galvanised G300 base configuration for general grain receival, silo aeration and stockfeed batching work, plan 12 to 16 weeks build-to-order from purchase order to bill of lading, plus 2 to 4 weeks main carriage to the receiving Australian port (Brisbane, Sydney, Melbourne, Adelaide, Fremantle, Geelong or one of the regional inland positions), plus 2 to 6 weeks installation and commissioning on site. Total project handover is typically 5 to 7 months from PO.

For the SBSF-1525 stitchwelder plus SB-ZF1500 longitudinal seam welder configured for 304L stainless food-grade flour mill plenum work, plan 14 to 18 weeks build. For the SBTF-1602 spiral tubeformer plus the SBTF-2020 large-diameter option for primary dust collection mains and pneumatic conveying envelope, plan 10 to 14 weeks. The SBPC1500 plasma cutter for fittings and transitions, the SBFB-1500 spiral fitting former for matched spiral fittings and the SBLR-600 laser welder for food-grade field welds run in parallel on the same factory order.

SBKJ engineers from the Box Hill North VIC office handle Australian commissioning and operator training in English on site, with scheduling around the November to January grain harvest peak and the September to November flour mill capital-works window. The SBKJ 12-hour engineering reply commitment applies through every stage of the project lifecycle — tender, design, fabrication, shipping, installation, commissioning and ongoing maintenance.

What to specify when you put a grain, flour, feed or pet food duct package out to tender

The single best lever for keeping a duct package on budget and on schedule is a tight specification at tender stage. The specification below is the SBKJ engineering template used as a starting point for new projects.

1. State the facility type (country silo, port terminal, flour mill, stockfeed mill, rendering plant, pet food extruder, pasta plant, oilseed crusher), the daily throughput, the product mix (grain class, flour grades, stockfeed product list including premix and medicated, pet food product list), and the operating hours and seasonal calendar.
2. Reference AS 1668.2, AS 4254, AS 1530.4, AS 3957, NFPA 660, NFPA 68, NFPA 69, AS/NZS 60079, AS 1940, AS 4036, AS 4037, AS 1716, AS 4332 (where applicable), AS 1851, AS 1657, AS 1318, FSANZ Food Standards Code 1.2.2 and 3.2.3 (where applicable), AS 5812 (where applicable), ISO 22000 and HACCP, and AS 4801 in the compliance clause.
3. Specify duct fabrication to AS 4254 with pressure class and leakage class for each duct system — Class A on dust extract and food-grade circuits, Class B on general circuits.
4. Specify material by zone — galvanised G300 for non-food, non-fat, low-chloride positions; 304L stainless above human-food product and in flour mill packing, pasta plant and stockfeed premix/medicated circuits; 316L stainless for chloride-exposed coastal positions, fat-exposed pet food extruder zones, high-temperature zones above 90 degrees C continuous, and corrosive vapour positions; conductive carbon steel for combustible dust extract trunks; refractory-lined carbon steel for rendering RTO and high-temperature exhaust segments; polypropylene or FRP for rendering scrubber and biofilter inlet.
5. Specify the dust hazard analysis under NFPA 660, including conductive bonded ducting verified less than 1 megohm to earth at every joint per AS/NZS 60079.14, NFPA 68 sized explosion venting on every dust collector and silo, NFPA 69 spark detection plus infrared spark-out injection upstream of every filter, rotary airlock or fast-acting chemical isolation between the collector and each branch, removal of ignition sources from the dust cloud zone, and a documented housekeeping protocol with the 3 millimetre maximum dust thickness limit on horizontal surfaces.
6. Specify the hazardous area classification under AS/NZS 60079.10.1 for the gas zones (hexane at oilseed crushers, phosphine at silo fumigation, ammonia at chiller engine rooms) and AS/NZS 60079.10.2 for the dust zones (every silo headspace, elevator leg, transfer point, sifter, purifier, roller mill, pellet cooler, kibble extruder, dust collector enclosure). IECEx Ex rating on every motor, light fitting, sensor, instrument and damper actuator in the affected zones.
7. Specify spark-resistant centrifugal fans (AMCA Type B or Type C aluminium impeller in steel housing) on every dust extract circuit serving grain, flour, bran, feed or kibble dust.
8. Specify the grain silo aeration plenum at 0.5 to 2 litres per second per stored tonne with passive or powered roof discharge, NFPA 68 sized explosion venting on silo top and side walls, and gas-tight fumigation isolation dampers for phosphine cycle integration.
9. Specify the grain dryer exhaust to AS 1318 industrial chimney with primary cyclone followed by NFPA 68 vented bag filter, AS 4036 compliant boiler combustion air supply, and downwind dispersal modelling cleared with the local EPA.
10. Specify the flour mill plenum and packing hall as 304L stainless with continuous welded seams (SBSF-1525 plus SB-ZF1500), internal grinding to Ra 0.8 micrometre or better, crevice-free TDF or flanged joints, FDA-listed gasketing, HEPA H13 or H14 final filter, 304L stainless smooth-welded supply duct downstream of the filter, and 10 to 15 pascals positive pressure relative to surrounding zones.
11. Specify the stockfeed mill premix and medicated feed circuits as physically segregated ducting under AS 5812 with dedicated dust collectors, dedicated exhaust fans and dedicated maintenance and cleaning protocols.
12. Specify the oilseed extraction building HVAC with 316L stainless on the hexane-exposed segments, AS/NZS 60079.10.1 Zone 1 hazardous area dossier on the extractor and condenser train, IECEx Ex e or Ex d motors, intrinsically safe instruments, bonded conductive ductwork verified less than 1 megohm to earth, and 12 to 20 ACH building ventilation to maintain ambient hexane below 25 percent LEL.
13. Specify the rendering plant two-stage odour control with high-strength NCG to RTO (316L stainless or refractory-lined inlet) and low-strength building air to packed-bed scrubber with biological polishing (316L or FRP inlet), AS 1318 compliant industrial chimney, and continuous emissions monitoring per state EPA conditions.
14. Specify the pet food extruder line as Class 2 grease duct under AS 1668.2 with 316L stainless throughout the extruder hood, drying tunnel exhaust, coater drum vent and cooler exhaust, sloped duct at 1:25 minimum to grease drain plug, daily wash-down provision, inspection cleanouts every 3 metres, in-line fat aerosol mist eliminator before any abatement equipment, and NFPA 660 controls on the kibble cooler and bagging line.
15. Specify the ammonia chiller engine room under AS 4332 with continuous purge ventilation, 25 ppm alarm, 150 ppm emergency evacuation, gas-tight isolation, intrinsically safe sensors, IECEx Ex e or Ex d motors and an emergency dump vent routed clear of occupied buildings.
16. Specify the commissioning sequence — AS 4254 leakage test, air balance, bonding verification, dust hazard analysis walk-through, environmental conditioning, regulatory and audit sign-off — and the as-built documentation pack.

Get an SBKJ grain, flour, feed or pet food duct package quotation →

FAQ

How combustible is grain and flour dust under NFPA 660?

Wheat dust, raw grain dust and milled flour are among the most reactive agricultural dusts in the world. Wheat flour typically tests Kst above 200 (NFPA 660 St-3 high-violence class). Raw grain dust commonly tests Kst 130 to 220 (St-2 to St-3). Minimum ignition energies sit between 30 and 100 millijoules — well within the energy of a static spark, a hot bearing, a welding spatter or a smouldering grain fragment. NFPA 660 (the 2025 consolidation of NFPA 484, 654, 655, 61 and 664), NFPA 68 explosion venting, NFPA 69 explosion prevention and AS/NZS 60079.10.2 dust zone classification all apply.

What stainless grade does SBKJ recommend for an Australian flour mill?

304L stainless (1.4307) as the baseline for all duct above open product, with 316L (1.4404) in chloride-exposed coastal mill positions (Newcastle, Brisbane, Geelong, Port Adelaide, Kwinana, Albany), fat-exposed positions (pet food extruder), high-temperature positions (above 90 degrees C continuous), and corrosive vapour positions. Galvanised G300 is acceptable in non-food, non-fat, low-chloride positions. Fabrication on the SBKJ SBSF-1525 stitchwelder plus SB-ZF1500 longitudinal seam welder with internal grinding to Ra 0.8 micrometre or better.

What hazardous area zone applies inside a grain silo or flour mill basement?

AS/NZS 60079.10.2 typically classifies the silo headspace and the silo wall cavity as Zone 21, the area around silo loading and discharge points as Zone 22, and the broader silo apron as Zone 22 or unclassified depending on housekeeping. The flour mill basement around the roller-mill grinders, sifters, purifiers and pneumatic conveying transfer points is typically Zone 21, with the broader mill floor at Zone 22. Phosphine fumigation events trigger a separate temporary hazardous-area boundary under AS/NZS 60079.10.1 with all personnel evacuated.

Is hexane really Zone 1 around soybean meal solvent extraction?

Yes. The LEL for n-hexane is 1.1 percent v/v and the flashpoint is minus 26 degrees C. The Safe Work Australia 8-hour WES is 50 ppm with a STEL of 125 ppm. The extractor vessel is internally Zone 0. The desolventiser-toaster shell, mineral oil scrubber and condensers are typically Zone 1. The broader extraction building is Zone 2 subject to ventilation. Every motor, instrument, ducting bond and damper actuator in Zone 1 must carry the appropriate IECEx Ex d or Ex e rating under AS/NZS 60079.10.1.

How is rendering plant odour managed?

Two-stage treatment train. High-strength NCG (cooker non-condensable gas, evaporator overhead, decanter vapour) to a regenerative thermal oxidiser at 800 to 850 degrees C residence 0.75 to 1.0 second. Low-strength building air to packed-bed wet scrubber with biological polishing or biofilter. 316L stainless or refractory-lined inlet ducting to the RTO. 316L or FRP inlet to the scrubber and biofilter. AS 1318 compliant industrial chimney for the discharge. Continuous emissions monitoring per state EPA conditions. ARA industry framework.

What is phosphine fumigation and how does it affect silo HVAC?

Phosphine (PH3) from aluminium phosphide or magnesium phosphide pellets (Pixarvin, Magtoxin, Quickphos, Gastoxin) released into a sealed silo at 200 to 800 ppm for 7 to 14 days. Safe Work Australia 8-hour WES 0.3 ppm, STEL 1 ppm. Implications: aeration locked out during hold, gas-tight isolation dampers, breathing-zone PH3 monitors with alarm, post-fumigation forced ventilation through scrubber or thermal destruction, AS 1716 SCBA for entry teams, fumigation event log integrated with site SCADA per Department of Agriculture export grain quarantine standards.

How is pet food extruder air handled differently from human-food flour mill air?

The extruder die plate releases superheated steam at 130 to 160 degrees C mixed with fat aerosol from rendered meat ingredients, the post-extrusion fat-coating drum atomises tallow or chicken fat at 60 to 80 degrees C, and the drying tunnel exhausts combustion products plus moisture at 110 to 130 degrees C. Material is 316L stainless throughout because fat acids attack 304L over time. The fat aerosol creates a Class 2 grease duct condition under AS 1668.2 — sloped 1:25 minimum to grease drain, daily wash-down, inspection cleanouts every 3 metres, in-line mist eliminator. Pet food kibble dust still tests Kst 150 to 200 (St-2 to St-3) so NFPA 660 combustible dust controls apply on the cooler, coater drum and bagging line.

What is the lead time for SBKJ machinery into an Australian grain or flour mill project?

SBAL-V galvanised G300 base 12 to 16 weeks build, plus 2 to 4 weeks main carriage to Australian port, plus 2 to 6 weeks installation. SBSF-1525 stitchwelder plus SB-ZF1500 in 304L stainless food-grade flour mill plenum configuration 14 to 18 weeks build. SBTF-1602 plus SBTF-2020 spiral tubeformer for primary dust collection mains 10 to 14 weeks. SBPC1500 plasma, SBFB-1500 spiral fitting and SBLR-600 laser welder run in parallel. SBKJ Box Hill North VIC engineers handle commissioning around the November to January grain harvest peak.