Pet Food & Animal Feed Manufacturing HVAC Duct Guide — Extrusion, Drying, Coating, Packaging

Why pet food and feed plants are an HVAC engineering challenge

A pet food or animal feed plant is one of the most demanding industrial HVAC environments a duct contractor will ever specify. Within a single building you can find a meat-and-bone-meal receiving bay at ambient temperature, a 120 degree C steam-and-fat extruder exhaust, an 80–110 degree C dryer plume carrying fines, a fat-coating drum venting oil aerosol, a vitamin premix room with explosive-dust-rated electrical, a grain elevator with silica-and-mycotoxin dust, a retort line venting saturated steam, a packaging room with modified atmosphere gas, and a chilled ingredient store at 2 degree C. Each of these zones drives a different duct material, gauge, velocity, jointing method and cleaning protocol. Specifying one HVAC system across all of them — galvanised spiral, single gauge, single velocity — is the most common mistake we see when we walk into Australian pet food sites for the first time.

This guide collects what SBKJ engineers have learned from supplying duct production machinery to contractors who have built and refurbished pet food plants for Mars Petcare in Wodonga Victoria, Nestle Purina PetCare in Blayney New South Wales, Real Pet Food Company sites in Sydney and Brisbane, Hypro Premium Pet Foods in Tumut New South Wales, Pacific Pet Foods in Bega, VetAlpha in Melbourne, Bell Pet Foods, Coprice Pet Foods, Whitebridge Pet Brands, Pet Treats Australia and the Black Hawk premium line, alongside stockfeed mills run by Ridley Corporation, Riverina, Cargill Australia, AGCO Feeds, South Coast Grain, Reno feed mills and the aquafeed plants operated by Skretting (Nutreco) and supplying Tassal salmon. The patterns are remarkably consistent across the sector — and so are the failure modes when ductwork is under-specified.

Read this guide as a planning document, not a substitute for a process engineer or a hazardous area classification study. Every plant has its own product mix, throughput, regulatory class and existing-building constraint. What we can give you is the framework — the standards, the material grades, the velocity and temperature ranges, the audit triggers — that lets you have an informed conversation with your process engineer, your fire engineer and your auditor.

Regulatory landscape — what governs pet food and feed manufacturing in Australia

Pet food and animal feed in Australia sit under a layered regulatory framework. None of the standards listed below are written as HVAC ductwork specifications, but together they constrain materials, layout, segregation, dust control, food contact surface hygiene and audit documentation in ways that flow straight through to the duct specification.

AS 5812 — Manufacturing and marketing of pet food

AS 5812:2017 is the Australian Standard for pet food manufacturing. It sits under the Pet Food Industry Association of Australia (PFIAA) voluntary certification scheme and is the closest thing pet food has to a binding production code in Australia. AS 5812 covers ingredient sourcing, manufacturing controls, traceability, labelling and recall — the operational backbone of any audited pet food plant. From an HVAC perspective, AS 5812 drives three things: cleanable, non-shedding, non-toxic surfaces above open product; segregation of incompatible product streams (raw meat from finished kibble, medicated from non-medicated); and documented pest control, which in practice means negative-pressure receiving bays and sealed dust collection.

AS 5812 is not law — there is no federal pet food law in Australia equivalent to the United States Food, Drug and Cosmetic Act provisions for animal food — but every major Australian pet food brand voluntarily certifies to it through PFIAA. If you are designing or refurbishing a plant intended for shelf placement in Coles, Woolworths, Petbarn or PETstock, AS 5812 compliance is a commercial gate, not an option.

AS 4674 — Construction and fit-out of food premises

AS 4674:2004 is the construction and fit-out standard that food safety auditors apply to building shells. While written primarily for human food premises, it is the standard most Australian state environmental health officers cite when reviewing pet food plant fit-out submissions. AS 4674 calls out wall, floor and ceiling materials; coving; drainage; pest exclusion; and — relevantly for HVAC — the requirement that overhead surfaces above open product be smooth, cleanable and non-shedding. Galvanised spiral duct with un-sealed seams running directly above an open extruder discharge is the most common AS 4674 finding we see in pet food audits.

HACCP and GFSI — global frameworks

Hazard Analysis Critical Control Point (HACCP) is the foundational food safety methodology used in every audited pet food and feed plant globally. HACCP-based plans require hazard analysis at each process step — including airborne contamination from overhead ductwork, cross-contamination between zones via shared supply air, and condensate drip from cold-line ductwork above warm process areas. Each of these is a documented hazard with a documented control measure in a mature plant.

The Global Food Safety Initiative (GFSI) is the benchmarking body for retailer-recognised food safety schemes — SQF, BRCGS, FSSC 22000, IFS. Most Australian pet food brands certify their plants under SQF or BRCGS, both GFSI-benchmarked. GFSI schemes inherit HACCP and add explicit physical contamination controls, including ductwork inspection frequency, cleaning records and material specifications for surfaces above product.

PFIAA — Pet Food Industry Association of Australia

The Pet Food Industry Association of Australia is the peak industry body for Australian pet food manufacturers. PFIAA administers the AS 5812 certification scheme, lobbies on industry regulation and publishes guidance for member plants. PFIAA member status is widely treated by retailers and consumers as a quality marker. From an HVAC perspective, PFIAA member plants are audited annually against AS 5812 — which means duct material specifications, cleaning logs and overhead surface inspections are part of the annual audit pack.

Feedsafe — Australian stockfeed mill certification

Feedsafe is the Stock Feed Manufacturers Council of Australia (SFMCA) certification scheme for stockfeed mills. It is a HACCP-based feed safety programme covering ingredient receiving, manufacturing, packaging and dispatch. Major Australian stockfeed producers — Ridley Corporation, Riverina, Cargill Australia, AGCO Feeds and most regional mills — are Feedsafe certified. Feedsafe drives three HVAC-relevant requirements: pest exclusion (sealed receiving, negative pressure), cross-contamination control (segregated air handling between medicated and non-medicated lines), and dust explosion prevention (cyclone-plus-baghouse on grain handling, full earth bonding per AS/NZS 60079).

AAFCO — Association of American Feed Control Officials

The Association of American Feed Control Officials publishes nutrient profiles, ingredient definitions and labelling guidance that are referenced globally — including in Australia — even though AAFCO is a United States voluntary body with no direct regulatory authority outside the United States. Many Australian pet food labels carry "formulated to meet AAFCO nutrient profiles" claims because export markets (United States, Canada, parts of South-East Asia) recognise AAFCO. AAFCO does not specify HVAC requirements directly, but its ingredient definitions — particularly for vitamin and mineral premixes — influence the dust profile and therefore the dust collection sizing in the premix room.

AS 1668.2 — Australian mechanical ventilation code

AS 1668.2:2024 The use of ventilation and airconditioning in buildings — Mechanical ventilation in buildings is the foundational Australian ventilation standard. It sets outdoor air rates per occupant, exhaust rates for kitchens and process areas, and the framework for car park and special-use ventilation. AS 1668.2 is what your local council building surveyor will apply to your plant's general ventilation. For a separate treatment, see our reference guide at AS 1668.2 — Australian Ventilation Code Reference.

NFPA 484 and AS/NZS 60079 — combustible dust and hazardous areas

NFPA 484 Standard for Combustible Metals and the broader NFPA 652/654/61 family on combustible dust are the United States benchmark for dust explosion prevention. Australian plants apply the same engineering principles under AS/NZS 4745:2012 Code of practice for handling combustible dusts and AS/NZS 60079.10.2 for hazardous area classification in dust atmospheres. Grain handling, premix rooms, dust collection ducts and the area around extruders that handle wheat, barley, soy, peas or lupins fall under these standards. The implication for ductwork: minimum trunk velocities of 18 m/s to prevent settling, full earth-bonding continuity, welded over bolted joints in dust-bearing duct, rotary valves as flame breaks at process boundaries, and explosion vents on baghouses.

Process zones — a walk through a pet food plant

To make the material specifications concrete, walk with us through a typical Australian dry pet food plant. The zone sequence is the same at Mars Petcare Wodonga, Nestle Purina Blayney, the Real Pet Food Company sites and most of the Hypro and Coprice plants. What differs is throughput, automation level, segregation between species (dog/cat) and whether wet line, treats line and aquafeed are co-located.

Grain receiving and storage

The plant begins at the truck tip — wheat, barley, corn, sorghum, rice, soy meal, pea protein and sometimes oats arrive in B-double bulk tippers. Truck tipping is one of the dustiest single events in the entire plant: hundreds of tonnes of grain dropping into a receiving hopper in under fifteen minutes, generating a dust cloud that can momentarily exceed the lower explosive limit if not captured. The receiving pit is on negative pressure, with a hood at the tip point ducted to a cyclone-plus-baghouse system rated for 25–50,000 m3/hr depending on the truck size and the receiving rate.

From the receiving pit, grain moves via bucket elevator or pneumatic conveying to silos. Bucket elevators are well-documented dust explosion initiators — most major grain dust explosions globally have originated in elevator legs — so every leg is fitted with explosion vents, monitored for bearing temperature, and connected to a dust collection trunk running at not less than 18 m/s. Pneumatic conveying lines are sealed and self-contained but vent to a baghouse at the destination silo.

Ductwork material in grain receiving is galvanised carbon steel as standard — there is no food-contact-adjacency concern in this zone because the grain is moving in fully enclosed conveying. What matters is heavy gauge (1.2 mm minimum on dust collection trunks against the 0.5–0.6 mm typical for low-pressure HVAC), welded seams over bolted, full earth-bonding, and explosion isolation devices at every transition into another fire compartment. Mycotoxins — particularly aflatoxin on corn and fumonisin on sorghum — are a documented concern in grain receiving, but they are controlled by ingredient quality assurance and not by ductwork specification. Silica from grain dust is a respirable hazard for operators but is captured in the same baghouse system that captures organic dust.

Ingredient dosing and premix

From the silos, ingredients move to the dosing floor where major ingredients are weighed and combined with minor ingredients and the vitamin/mineral premix. The premix area is the highest-risk dust zone in the plant from a deflagration perspective. Vitamin and mineral premixes are formulated to AAFCO nutrient profiles and supplied by Australian premix specialists, and they contain finely milled minerals (calcium carbonate, dicalcium phosphate, zinc oxide) along with vitamin A, D3, E, B-complex carriers and trace minerals. Particle sizes are typically below 100 micron with significant sub-50 micron fines, and Minimum Ignition Energy (MIE) values for some premixes are low enough to be ignited by ordinary electrostatic discharge.

The premix room is therefore classified as Zone 22 or Zone 21 dust atmosphere under AS/NZS 60079.10.2 depending on operations, with all electrical fittings rated accordingly and all metal ductwork bonded and earthed. Local capture hoods at every transfer point — bag dump, weigh hopper, mixer charge — duct to a dedicated baghouse that is never shared with the main grain system, because the dust characteristics and the cleaning frequency are different. Filter cages in this baghouse are stainless rather than galvanised because the trace minerals are mildly hygroscopic and chloride-bearing premixes accelerate galvanised corrosion. Ducting itself is 304 stainless welded with a sloped pitch toward a cleanout to allow accumulated dust to be vacuumed out during shutdown.

Mixer and pre-conditioner

The mixer combines major ingredients, minor ingredients and premix into the final formulation, then the pre-conditioner adds steam and water to hydrate the meal before extrusion. The pre-conditioner is the first significant heat-and-moisture source in the plant — steam at 100–120 degree C is injected directly into a continuously stirred horizontal tank, and the exit meal is at 80–90 degree C and 25–30 percent moisture. Vapour offgas from the pre-conditioner is captured by a local exhaust hood and ducted, in stainless, to either a wet scrubber or to combine with the extruder exhaust before the stack. Combining is the common option in Australian plants because the combined stream has consistent temperature and aerosol characteristics for treatment.

Extruder and cutter

The extruder is the heart of a dry pet food plant. A twin-screw or single-screw extruder takes the pre-conditioned meal at 80–90 degree C and forces it through a die at 130–160 degree C and 30–50 bar, producing expanded kibble that is cut off at the die face by a rotating knife. The expansion happens because the rapid pressure drop at the die exit vapourises the moisture, creating the cellular structure that gives kibble its texture.

Extruder exhaust is the most demanding ductwork environment in the plant. The exhaust gas leaving the cutter housing is typically 90–120 degree C, saturated with steam at extrusion pressure flash-off, and carrying fat aerosol from any fat injected into the extruder barrel along with meal fines from the cut. The combination of high temperature, water vapour and fat aerosol is extremely aggressive to galvanised steel — zinc reacts with the organic acids in the fat, water condenses out on the duct walls at the first cool spot, and corrosion at the seam laps begins within 18–36 months in our experience. Plants that started with galvanised extruder exhaust frequently rebuild it in stainless within five years.

The specification for extruder exhaust is 304 stainless welded duct, 1.2 mm minimum, with a steam knockout pot upstream of any control damper, cleanout doors every 6 m, and a slope of not less than 1 in 50 toward a condensate drain. Insulation is optional but recommended to prevent re-condensation downstream of the knockout. Treatment before the stack is typically a wet scrubber sized for fat aerosol and a residual particulate filter; some larger plants use an electrostatic precipitator for fat aerosol with a downstream high-efficiency filter for fines. The stack itself is stainless and sloped back to a sump.

Above the extruder and cutter, supply air is required to make up for the exhaust and to maintain operator-area temperature in summer. Australian plants in Wodonga, Blayney and Tumut all run heat-recovery on the extruder exhaust to pre-heat winter make-up air, which means a stainless cross-flow plate exchanger and double-skin ductwork on the supply side as well. The supply ductwork above the cutter is also stainless because it sits directly over open product and is subject to AS 5812 cleanability requirements.

Dryer

Wet kibble leaving the cutter at 25 percent moisture is conveyed to the dryer where it is dried to 8–10 percent moisture for shelf stability. Pet food dryers are either single-pass or multi-pass belt dryers (the dominant technology in Australia), or — for smaller premium plants — drum dryers. Drying air enters at 110–150 degree C and exits at 80–110 degree C, carrying water vapour and a load of fines that have separated from the kibble surface as it shrinks during drying.

Dryer exhaust ductwork is the highest-temperature ducting in the plant. The exhaust is below the dryer inlet temperature but still high enough that galvanised steel is not the right material — the zinc coating degrades above 200 degree C and the seam joints lose integrity in the saturated-steam-plus-fines environment well below that. The standard specification is 304 stainless welded, insulated externally, with a cyclone-plus-baghouse train before the stack and a heat-recovery exchanger upstream of the baghouse to pre-heat make-up air or to pre-heat the next dryer stage. Dryer exhaust runs in our experience at 12–18 m/s — high enough to keep fines entrained to the cyclone, low enough to manage erosion at elbows and dampers.

For dryers where the exhaust at the burner side may exceed 150 degree C — typical of multi-pass dryers with a first-stage at 160–180 degree C — the first 6 m of duct is either 316 stainless or refractory-lined carbon steel. The transition to 304 occurs after the first heat-recovery stage drops the temperature below 150 degree C. Cleanout doors are essential because fines build up at every elbow and at the cyclone inlet vanes, and a build-up of organic fines in a hot duct is a smoulder hazard.

Cooler

From the dryer, kibble at 80–90 degree C is conveyed to a cooler — typically a counterflow vertical cooler — where ambient air is drawn through the bed of warm kibble to drop the temperature to within 10 degree C of ambient. Cooler exhaust is at 40–60 degree C, dry (the kibble is already dried) and carries a moderate load of fines. The duct material here can be galvanised steel because the temperature, humidity and fat content are all low, but a baghouse downstream of the cooler is non-negotiable — uncaptured cooler exhaust is a dust nuisance and a deflagration risk. Many Australian plants run their cooler exhaust into the same baghouse train as the dryer with a tee upstream of the cyclone; this is acceptable provided the baghouse is sized for the combined air volume and the dust characteristics are similar.

Coating drum (fat and palatant application)

After cooling, kibble enters the coating drum where fat (chicken fat, tallow, fish oil) and palatant (digest, yeast extract, hydrolysed protein) are sprayed onto the kibble surface to give the finished product its flavour and palatability. The coating drum is typically a horizontal rotating cylinder with spray nozzles arranged along the top. Kibble enters at one end, falls through the spray curtain, and exits at the other end with a 4–8 percent fat surface coating.

The coating drum is the second-most-aggressive duct environment in the plant after the extruder. The vent stream is at ambient to 60 degree C and is loaded with fat aerosol from the spray atomisation. The aerosol condenses on cool duct surfaces, runs downhill, accumulates as a viscous fat film, and — in extreme cases — generates a thick coating that progressively narrows the duct cross-section. Galvanised duct in this service fails within 12–24 months. The standard specification is 304 stainless welded duct with a sloped pitch toward a drain, a fat-rated wet scrubber or fat-coalescing filter before the stack, and a cleanout protocol that includes hot caustic wash on a quarterly basis.

The coating duct trunk must never be shared with dry product zones. Fat aerosol that drifts back into a dryer or packaging area creates a contamination hazard and an ignition risk. Coating drum exhaust has its own dedicated stack.

Sieve, screen and bulk storage

Coated kibble passes through a final sieve to remove broken pieces and oversized agglomerates, then conveys to finished-product bins for short-term storage before packaging. The conveying air system is sealed pneumatic on premium plants, mechanical bucket elevator on others, and either way is enclosed with a local capture vent ducted to the cooler baghouse. The finished-product bins are typically vented to a small dedicated bin-vent filter.

Packaging

Packaging is the cleanest air environment in the plant. Bag and pouch lines run at ambient temperature with low dust loading from kibble fragments at the filler nozzle. AS 1668.2 outdoor air rates per occupant are sufficient for general ventilation, with local capture at the filler nozzle ducted to a small dedicated baghouse. Ductwork in the packaging area is galvanised spiral with sealed seams, run at low velocity (6–8 m/s) and silenced because the packaging area is the noisiest part of the dry plant.

Modified atmosphere packaging (MAP) is used on premium dog food and treats lines to extend shelf life by displacing oxygen with nitrogen or a nitrogen/carbon dioxide blend. MAP zones require gas detection — low-oxygen alarm and high-CO2 alarm — and a dedicated exhaust system independent of the general packaging ventilation. The MAP exhaust duct is galvanised, low velocity, and discharges through the roof at a height that prevents recirculation.

Wet food and retort line

Wet pet food — pouch and can lines — runs through a separate cooking and retort process. The pouch line fills, seals and then transfers pouches to a retort autoclave for thermal processing at 121 degree C for a time sufficient for commercial sterility (typically 30–60 minutes depending on pouch size and product). The retort vents saturated steam at 100–130 degree C, and the cookers feeding the retort vent low-pressure steam at 80–100 degree C.

Retort and cooker exhaust ductwork is 304 stainless welded with condensate drains at every low point and a discharge stack that releases at safe height. The duct cannot be shared with dry-product systems and must have isolating dampers to prevent steam migration during retort cycle changes. The wet line is also a Listeria and Salmonella control zone, and ductwork above the open-product pouch filler before sealing is subject to the highest cleanability standards — typically 304 stainless with crevice-free welded seams and a clean-in-place spray ball system on duct sections above the filler.

Cold storage of fresh ingredients

Fresh meat, poultry and fish ingredients arrive frozen and are stored in plant-side chiller and freezer rooms at minus 18 degree C and plus 2 to plus 4 degree C respectively. Ductwork in these rooms is its own engineering discipline — insulated stainless, vapour-barrier-jacketed, with anti-condensate detailing at every penetration through warm-zone walls. Cold storage ductwork specifications are out of scope for this guide; see our companion piece at Cold Storage and Cold Chain HVAC Duct Guide for the full treatment.

Material selection — the four-grade system

Across the pet food plant, four material grades cover every duct application. The challenge is mapping the right grade to the right zone — and resisting the cost pressure to specify galvanised everywhere.

Galvanised carbon steel (Z275 or Z350 G300)

Hot-dip galvanised carbon steel with zinc coating of 275 g/m2 (Z275) or 350 g/m2 (Z350) on a G300 steel substrate is the workhorse material for general ventilation, low-temperature exhaust, dust collection on dry zones and packaging area ductwork. Galvanised is cheap, easy to fabricate, lockformed or TDF-flanged, and has acceptable corrosion life — 15–25 years — in non-aggressive service. Where it fails in pet food plants is wherever steam, fat aerosol, organic acids or temperatures above 200 degree C are present. Specify galvanised in grain receiving, packaging supply and return, MAP exhaust, general make-up air, cooler exhaust (with caveats) and dispatch area ventilation.

304 stainless steel

304 stainless (austenitic chrome-nickel) is the standard for food-contact-adjacent ductwork and for moderately aggressive service. 304 handles extruder exhaust, dryer exhaust below 150 degree C, coating drum exhaust, cooker exhaust, retort exhaust below 150 degree C, supply air above open product, and any ductwork that will be cleaned with caustic or acidic detergents. 304 is welded, brake-formed or roll-formed into rectangular and spiral duct, with longitudinal seam welds for full sanitary service. The cost premium over galvanised is typically 3–5x at the duct level but is recovered within 5–8 years through avoided replacement.

316 stainless steel

316 stainless adds molybdenum to the 304 base composition, improving resistance to chloride pitting and to organic acids. Specify 316 where chloride is present — coastal plants, seawater spray, sodium chloride in product, certain palatant chemistries — and for the hottest dryer exhaust sections above 150 degree C. 316 is more expensive than 304 (typically 1.4–1.6x at material level) and the fabrication is identical, so the decision is on service chemistry not on workability. In aquafeed plants — Skretting (Nutreco) in Western Australia, smaller aquafeed operations supplying Tassal salmon — 316 is the default for any exhaust because of fish meal volatiles and the chloride environment.

Refractory-lined carbon steel

For dryer exhaust temperatures sustained above 200 degree C, neither galvanised nor unlined 304 is appropriate. Refractory-lined carbon steel — a 6 mm carbon steel outer with a 50–75 mm ceramic fibre or castable refractory inner — handles temperatures up to 600 degree C with acceptable life. The fabrication is heavier and the duct is essentially non-flexible, so cost-effective installation depends on minimising flange joints and on careful expansion-joint design. Refractory-lined duct is normally limited to the first dryer pass exhaust on multi-pass dryers and to specialty applications such as roasted-treat lines.

Velocity, gauge and pressure class

Material selection alone is not enough — gauge, velocity and pressure class must match the service. The summary table for pet food and feed plants is:

• General ventilation supply and return — 4–8 m/s, 0.6–0.8 mm galvanised, low pressure class.
• Packaging local exhaust — 8–12 m/s, 0.8 mm galvanised, low pressure class with silencing.
• Cooler exhaust — 12–15 m/s, 0.8–1.0 mm galvanised, medium pressure class.
• Dryer exhaust — 14–18 m/s, 1.2 mm 304 stainless welded, medium pressure class, externally insulated.
• Extruder exhaust — 12–15 m/s, 1.2–1.5 mm 304 stainless welded, medium pressure class, externally insulated, sloped to drain.
• Coating drum exhaust — 10–14 m/s, 1.2 mm 304 stainless welded, medium pressure class, sloped to drain.
• Grain dust collection trunks — 18–22 m/s, 1.5 mm galvanised welded or bolted with bonded seams, medium pressure, explosion-vented baghouse.
• Premix dust collection — 18–22 m/s, 1.2 mm 304 stainless welded, medium pressure, dedicated baghouse, full earth bonding.
• Retort and cooker exhaust — 12–15 m/s, 1.2 mm 304 stainless welded, medium pressure, sloped to drain.
• Cold storage — 4–6 m/s, insulated stainless or insulated galvanised, with vapour barrier — see cold storage guide.

The 18 m/s minimum on dust collection is not aesthetic — below that velocity, fines settle out in the duct, accumulating as a layer that eventually narrows the duct cross-section, increasing velocity in the remaining bore until the system reaches steady state. The accumulated layer is also a fuel source. Above 22 m/s, erosion at elbows becomes the limiting factor and abrasion-resistant elbow plates become economic. The 18–22 m/s window is the sweet spot for most pet food and feed dust applications.

Jointing methods — welded versus flanged versus lockformed

How the duct is joined matters as much as what it is made of. Three jointing systems dominate pet food and feed ductwork. Lockformed seams (Pittsburgh, snap-lock, button-punch) are economical, fast and acceptable for low-pressure general ventilation in dry zones — not appropriate for steam, fat aerosol, dust collection or sanitary services because the crimp leaves microscopic gaps that harbour residue. Specify for general supply, return, packaging and dispatch. TDF (Transverse Duct Flange) is the integrated rectangular flange system — flanges roll-formed onto duct ends and bolted at site with corner pieces and gasket. TDF is the rectangular standard across Australian commercial HVAC and acceptable for most pet food zones except the highest-grade sanitary and dust-collection services. Welded seams (TIG longitudinal, MIG circumferential) are mandatory in sanitary zones — coater, extruder exhaust, dryer exhaust, retort, cooker, wet line above open product. Round spiral duct gets a TIG longitudinal seam weld during forming; rectangular duct gets TIG corner welds and MIG circumferential welds at joints. Welded is the only acceptable construction in extruder exhaust, coater exhaust and dust collection trunks in deflagration zones. Cost premium 1.5–2x over lockformed; avoided cost is residue accumulation, leak finding, audit findings and rebuild.

Hazardous area classification — what's Zone 21, Zone 22 and what isn't

AS/NZS 60079.10.2 Explosive atmospheres Part 10.2 Classification of areas — Explosive dust atmospheres is the standard most Australian pet food and feed plants apply for dust hazardous area classification. The three zone definitions matter:

• Zone 20 — explosive dust atmosphere present continuously, frequently or for long periods. Inside a baghouse, inside a silo, inside a mixer headspace, inside dust collection ducting in operation.
• Zone 21 — explosive dust atmosphere likely to occur in normal operation occasionally. Around a baghouse cleanout door during cleaning, around an open bag-dump station, around an exposed transfer point.
• Zone 22 — explosive dust atmosphere not likely to occur in normal operation, and if it does, will persist only briefly. General premix room floor, general grain receiving floor, packaging area near filler nozzle.

The duct itself is normally Zone 20 inside (the explosive dust atmosphere is continuously present during operation) and Zone 21 or 22 outside. The implication for hardware is on the electrical fittings, fans, motors and instruments associated with the ductwork — these must be rated Ex tD or Ex tb to the appropriate zone. The duct material itself is not "rated" in the hazardous-area sense, but the duct construction must support the zone by being bonded, earthed, leak-tight and free of internal traps that allow dust to accumulate.

Earth bonding is the single most overlooked detail. Every metal duct section, flange, support bracket and fan housing must be electrically continuous to earth, with bonding straps across flange joints and continuity verified at commissioning and on a documented periodic basis thereafter. AS/NZS 60079.14 sets the bonding requirements; SBKJ duct lines fabricate earth-continuity lugs as standard on grain-handling and premix ductwork.

Dust collection and acoustic specification

Pet food and feed plants run three main dust-collection technologies, often in series. Cyclones are mechanical separators using centrifugal force; efficient down to about 10 micron, they are universally used as primary separators upstream of a baghouse, extending bag life. Specify galvanised or epoxy-coated carbon steel for grain cyclones, 304 stainless for dryer/cooler, 316 stainless for aquafeed. Baghouses are the workhorse for fine particles with pulse-jet cleaned bag filters down to 1–3 micron — polyester for general dust, PTFE for high-temperature dryer exhaust, PP/PTFE for premix; housings galvanised for grain, 304 stainless for premix/dryer, with rotary valves and explosion vents per AS/NZS 4745. Wet scrubbers handle fat aerosol from the coater, sticky palatant fines and odour-control duties — venturi and packed-tower scrubbers in 304/316 stainless with caustic or surfactant scrubber liquor. The wet scrubber is the only acceptable technology on coater exhaust.

Acoustic: pet food and feed plants run NC-45 to NC-55 typical production floor, NC-35 to NC-40 control rooms and labs. Specify duct silencers on every fan above 7.5 kW, lag any duct passing through a control room with 50 mm fibreglass and foil outer, and avoid running high-velocity dust collection trunks through occupied office areas — where unavoidable, use double-skin duct with 25–50 mm acoustic infill.

The Australian pet food sector — who manufactures and where

Australian pet food manufacturing is dominated by a handful of large multinational and domestic producers, supported by a long tail of mid-size and specialist plants. The HVAC ductwork specifications across the sector are remarkably consistent because the regulatory frame (AS 5812, PFIAA, GFSI) and the process technology (extrusion-based dry kibble, retort-based wet) are the same across plants.

Mars Petcare Australia (Wodonga VIC) operates one of the largest pet food plants in the Southern Hemisphere, producing Pedigree, Whiskas, Royal Canin and other Mars brands. The Wodonga plant runs multiple extrusion lines for dry kibble alongside wet pouch and can operation, with full grain handling, premix preparation, coating, drying, packaging and dispatch on one integrated site. AS 5812 and GFSI certified.

Nestle Purina PetCare Australia (Blayney NSW) operates a large pet food plant in central-west NSW producing Purina dry and wet pet food. Blayney has been in operation since the 1980s and includes multiple extrusion lines, dryers, coaters and packaging halls. PFIAA certified.

Real Pet Food Company (Sydney and Brisbane) is the parent of V.I.P. Petfoods and specialises in chilled and fresh dog food alongside dry kibble, adding significant cold storage and fresh meat processing footprint compared with purely dry operations.

Pacific Pet Foods (Bega NSW) operates a pet food plant on the NSW south coast with strengths in mid-tier dog and cat food. Hypro Premium Pet Foods (Tumut NSW) supplies premium dog food including the Black Hawk brand, with the premium positioning driving tighter ingredient segregation. VetAlpha (Melbourne VIC) is a premium dog food manufacturer focused on the veterinary and specialty retail channel. Whitebridge Pet Brands distributes premium pet food including Stay Loyal and ZiwiPeak distribution. Bell Pet Foods handles private-label for supermarket house brands; Pet Treats Australia specialises in jerky and dental chews; Coprice Pet Foods has both pet food and stockfeed product lines. Each applies the same AS 5812, AS 4674 and PFIAA framework at smaller scale.

The Australian stockfeed sector — cattle, sheep, poultry, pig

Animal feed manufacturing in Australia is dominated by Ridley Corporation Australia, the largest stockfeed manufacturer with mills at Hallam Victoria, Cobram, Brisbane and other regional sites, supplying cattle, sheep, poultry, pig and aquafeed. Ridley mills are Feedsafe certified. Cargill Australia operates stockfeed manufacturing at Westonia in Western Australia and Footscray in Victoria, applying global Cargill HVAC standards. Riverina (NSW) supplies the dairy, beef, sheep and poultry sectors across NSW and Queensland. AGCO Feeds (Vic), South Coast Grain (NSW) and the network of Reno feed mills across regional NSW and Queensland round out the sector. The HVAC framework is the same as pet food at the front end (grain receiving, premix, mixing); the back end is simpler because stockfeed is pelleted rather than extruded and is bulk-shipped rather than packaged at retail format.

The Australian aquafeed sector

Aquafeed manufacturing — feed for salmon, trout, barramundi and other aquaculture species — is a small but high-value subset of Australian feed manufacturing. The dominant player is Skretting, a division of the Dutch company Nutreco, which operates an aquafeed plant in Western Australia supplying the Tasmanian salmon industry (Tassal in particular) and selected export markets. Aquafeed production uses higher-fat extrusion and oil-coating technology than mainstream pet food, with higher coater throughput per unit of dry product, which intensifies the fat-aerosol load on the coater exhaust. Aquafeed plants also handle fish meal and fish oil — both highly volatile sources of odour — which typically requires a thermal oxidiser or biofilter on the main exhaust stack rather than the wet scrubber more common on land-animal feed. The chloride environment in aquafeed plants drives 316 stainless rather than 304 for most exhaust ductwork. For a separate treatment, see our companion piece at Aquaculture and Seafood Processing HVAC Duct Guide.

Cross-contamination and segregation — the audit hot spots

Across pet food and feed plants, the most consistent audit findings — under AS 5812, PFIAA, GFSI/SQF and Feedsafe — are cross-contamination via shared HVAC. The hot spots:

• Shared supply air across allergen lines — fish, beef, chicken, lamb, salmon meal cross-contamination via shared supply air ductwork is a documented finding in audits. Premium plants run dedicated supply air per allergen line, with sealed return-air systems and HEPA filtration where pouch lines for hypoallergenic single-protein formulations are co-located with general production.
• Medicated and non-medicated stockfeed cross-contamination — Feedsafe specifically addresses cross-contamination of medicated and non-medicated stockfeed via shared dust collection, pneumatic conveying or packaging. Most modern Australian mills run dedicated systems for medicated production, with documented flush-out protocols at species changeover.
• Dust drift from raw meal areas into kibble cooling — uncontrolled return air from raw meal premix areas drifts into the cooler floor and contaminates finished kibble. Negative-pressure premix rooms and sealed return-air systems are the fix.
• Condensate drip from cold-line ducting above warm process areas — chilled supply air ductwork running across a warm extruder hall will condense moisture on the outer surface. Without anti-condensate insulation and a drip-tray detail at every penetration, the condensate drips onto open product and creates a microbiological hazard.
• Fat aerosol back-drift from coater exhaust into packaging — coater exhaust stacks placed upwind of packaging area outdoor air intakes pull fat aerosol back into the packaging supply air. Stack-and-intake separation per AS 1668.2 is mandatory.

SBKJ machine configuration for pet food and feed ductwork

SBKJ Group manufactures the duct production machinery used by HVAC contractors building and refurbishing pet food and animal feed plants worldwide. The machinery configuration we recommend for this sector reflects the four-material framework — galvanised general ventilation, 304 stainless food-contact-adjacent and process exhaust, 316 stainless aquafeed and high-chloride, refractory-lined for the hottest dryer service.

SBAL-V Auto Duct Production Line — Galvanised plus stainless option

The SBKJ SBAL-V is an auto rectangular duct production line that takes coil, levels, shears, notches, brake-forms and seams into Pittsburgh-lock or TDF-flanged rectangular duct. The standard configuration handles galvanised carbon steel coil from 0.5 to 1.5 mm thickness; the optional stainless package replaces the coil rollers and the cutting tools with stainless-compatible versions, allowing 304 and 316 to be processed on the same line. The SBAL-V handles single-shift output of around 600–800 m2 of finished duct depending on size mix, which is sufficient for most Australian HVAC contractors building pet food and feed plant duct packages. The stainless option also includes upgraded forming geometry for the slightly different work-hardening behaviour of 304 versus galvanised, so the corner radii and the flange forms remain within tolerance across both materials.

SBTF-1602 Spiral Tubeformer — Round duct 80 to 1,600 mm

The SBKJ SBTF-1602 spiral tubeformer produces round spiral duct from 80 mm to 1,600 mm diameter in galvanised, aluminium and stainless coil. The standard four-bend forming head handles all common pet food and feed plant round duct applications: grain receiving dust collection trunks, dryer exhaust trunks, coater exhaust, premix dust collection, and all general round supply and return ductwork. The integrated cutoff and end-finishing produces ready-to-install lengths up to 6 m without site joins, which improves both aesthetics and air-tightness in long trunk runs.

TIG longitudinal seam welder for sanitary zones

For ductwork in the highest-cleanability zones — coater exhaust, retort exhaust, supply air directly above the cutter and packaging filler, wet line — the seam must be fully welded and crevice-free. SBKJ supplies an integrated TIG longitudinal seam welder option for the spiral tubeformer and for the rectangular line, producing food-grade welded seams that meet AS 5812 cleanability and GFSI/SQF audit requirements. The welded seam removes the residue-trapping geometry of a crimped or button-punched joint and enables clean-in-place protocols on the inside of the duct.

Recommended ancillaries

For a pet food or feed plant project, SBKJ also recommends the auto coil-cutting and slitting line to manage the mixed coil stock (galvanised plus 304 plus 316), and the auto-feed flange former for site-mounted welded flanges on stainless trunk runs. Ancillary tooling — a stainless-grade lockformer for sanitary lock seams on small-diameter duct, a hand-portable TIG kit for site repair welds — completes the production package.

For full machine specifications and pricing, see the SBKJ machine catalogue or the related insight How to Choose an Auto Duct Production Line.

Compliance documentation — what the auditor will ask for

A pet food or feed plant audit — PFIAA, Feedsafe, SQF, BRCGS, FSSC 22000 — will reach into the HVAC documentation pack. Prepare in advance:

• Duct register — a one-page-per-zone register listing every duct section by drawing number, material grade, gauge, length, hazardous area zone, food contact class and cleaning frequency.
• As-built drawings — current as-built ductwork drawings reflecting any modifications since original construction.
• Material certificates — mill certificates for stainless coil used in food-contact-adjacent zones; galvanising certificates for general zones.
• Welder qualifications — TIG welder qualifications under AS/NZS 1554.6 for stainless welded ductwork.
• Earth bonding records — initial commissioning continuity test results and periodic re-test results for all dust handling ductwork.
• Cleaning records — completed cleaning logs against the HACCP-mandated cleaning frequency for each duct section.
• Hazardous area classification document — the AS/NZS 60079.10.2 dust HAC study for the plant, with current revision date.
• Explosion vent maintenance — annual inspection records for baghouse explosion vents and rotary valve flame breaks.
• Allergen segregation — air-handling segregation documentation between allergen-bearing and allergen-free lines.

Common failure modes

The most common ductwork failure modes we see in Australian pet food and feed plants: galvanised extruder exhaust corroding at seams within 24 months (rebuild in 304 welded); fat film narrowing coater exhaust to half cross-section (positive slope to drain plus quarterly hot-caustic clean); baghouse explosion vents firing during normal operation (raise trunk velocity above 18 m/s, verify earth bonding); mould on chilled-supply duct across warm extruder hall (closed-cell foam with vapour barrier); audit non-conformance on cleanability of duct above pouch filler (304 welded with clean-in-place); acoustic complaint from operator break room next to dust collection fan (in-line silencer plus lagging); cross-contamination between dog and cat lines via shared return air (dedicated return per allergen line). Every one is preventable at design stage — the 10–20 percent design-stage premium beats rebuild plus business interruption plus audit non-conformance.

Capital cost benchmarks

For a new mid-sized Australian pet food plant — say 80,000 tonne per year of dry kibble — the ductwork package typically costs between A$1.5 million and A$3.5 million installed, depending on the share of stainless, the dust collection scope and heat-recovery integration. Within this: general ventilation A$300–600k galvanised; extruder/dryer/cooler/coater exhaust A$500–1,200k 304 stainless welded; grain dust collection A$300–700k galvanised welded with cyclones and baghouse; premix dust collection A$100–300k 304 stainless welded; wet line and retort A$200–400k 304 stainless welded; specialty (refractory-lined, heat recovery, wet scrubber) A$200–500k. Refurbishments typically range A$200–800k depending on scope.

How SBKJ supports the project

SBKJ Group supplies the duct production machinery — SBAL-V auto rectangular line, SBTF-1602 spiral tubeformer, TIG seam welder for sanitary zones — to HVAC contractors building and refurbishing pet food and animal feed plants. We equip the contractors who fabricate; we do not fabricate end-customer ductwork ourselves. Commissioning, training and parts are supported from the Box Hill North VIC office. The full catalogue is at machines, pricing at SBKJ Pricing and Lead Time, and background at About SBKJ Group.

How SBKJ scores against this checklist

If you are an HVAC contractor evaluating duct machinery options for a pet food or feed plant project, here is how the SBKJ machinery scores against the requirements set out in this guide:

• Material flexibility — SBAL-V handles galvanised, 304 stainless, 316 stainless and aluminium on the same line with tooling change-out. SBTF-1602 produces round duct from 80 to 1,600 mm in the same material range.
• Sanitary seam capability — integrated TIG longitudinal seam welder option for sanitary zones produces crevice-free welded seams compliant with AS 5812 and GFSI cleanability requirements.
• Earth-bonding fabrication — earth-continuity lugs fabricated as standard on grain-handling and premix ductwork, supporting AS/NZS 60079.14 commissioning.
• Australian support — full machinery sales, commissioning, training and parts support from the SBKJ Group office in Box Hill North VIC.
• Output capacity — single-shift production of 600–800 m2 of rectangular duct and 400–600 m of spiral duct sufficient to support mid-sized Australian pet food and feed plant projects with single-contractor delivery.

Talk to an SBKJ engineer about a pet food or feed plant project →

FAQ

What HVAC material should be used in a pet food extruder room?

304 stainless steel is the minimum standard for extruder room exhaust ducting in pet food plants. Extruder exhaust runs 90–120 degree C with steam, fat aerosol and meal carryover — galvanised duct corrodes at the seams within 18–36 months in this service. For dryer exhaust above 150 degree C, transition to 316 stainless or refractory-lined ductwork. SBKJ supplies the SBAL-V auto duct line with a 304 stainless coil option for sanitary zones and a TIG seam welder for fully sealed seams.

Does AS 5812 require stainless steel ductwork?

AS 5812:2017 Manufacturing and marketing of pet food does not prescribe a single material, but it requires food contact and contact-adjacent surfaces to be cleanable, non-toxic and non-shedding. In practice, audited Australian plants — including Mars Petcare Wodonga and Nestle Purina Blayney — use 304 stainless on supply air in the cooking zone, coater, packaging and wet line, and galvanised on general ventilation where there is no product splash or steam exposure. AS 4674 Construction of food premises governs the broader building shell.

What does Feedsafe certification require for ventilation in a stockfeed mill?

Feedsafe requires a HACCP-based feed safety plan covering ingredient receiving, manufacturing, packaging and dispatch. Ventilation requirements appear under pest control (negative-pressure receiving, sealed dust collection), cross-contamination control (separation between medicated and non-medicated lines), and dust explosion prevention. Most Ridley, Riverina and Cargill mills run cyclone-plus-baghouse on grain receiving and pneumatic conveying with full earth bonding per AS/NZS 60079.

What is the explosion risk in a feed mill and how does ductwork mitigate it?

Grain dust, soy hulls, pea protein and certain animal protein powders are combustible dusts under NFPA 484 and AS/NZS 4745. Mitigation: keep ducting velocity above 18 m/s to prevent settling, bond and earth all metal sections per AS/NZS 60079.14, fit explosion vents on baghouses, use rotary valves as flame breaks at process boundaries, and prefer welded seams over screwed joints in dust handling ducts.

How does SBKJ ductwork suit Australian pet food and feed plants?

The SBKJ SBAL-V auto duct production line handles 0.5–1.5 mm coil in galvanised or 304 stainless, producing pittsburgh-lock or TDF-flanged rectangular duct sized for Australian floor plans. SBTF-1602 spiral tubeformer produces round duct from 80 to 1,600 mm in galvanised, aluminium or stainless for grain receiving, dryer exhaust and dust collection trunks. For sanitary zones — coater, packaging, wet line, retort — SBKJ supplies a TIG longitudinal seam welder for fully sealed, crevice-free duct. The full machine fleet is supported from SBKJ's Box Hill North VIC office.