Specialty Chemicals, Petrochemical, Agrochemical & Industrial Gas HVAC Ductwork — Australian Manufacturing Guide

Why chemical HVAC is different

HVAC ductwork in a chemical manufacturing plant is not the same engineering discipline as HVAC in a commercial office tower, a cleanroom, a hospital or a data centre. The ductwork in a chemistry building has to survive concurrent attack from acids, alkalis, organic solvents and elevated temperature; it has to function as a safety-critical layer of protection rather than comfort cooling; it has to integrate with gas detection, fail-safe damper logic, hazardous-area zoning and an emergency ventilation regime that steps from a quiet 8 air changes per hour to 30 air changes per hour the moment a leak is detected. The documentation that surrounds it — Safety Case extracts, welder qualifications, IECEx fan certificates, AS/NZS 60079 zone drawings, AS 1940 storage registers, AS 4332 cylinder-storage layouts, AS 3780 corrosive registers and ADG 7.9 dangerous-goods manifests — is the difference between a plant that runs for thirty years and one that becomes an Australian Work Health and Safety prosecution.

This guide is written for the engineers, project managers, EHS leads and procurement specialists who plan, build, operate or refurbish chemical manufacturing facilities in Australia — the explosives precincts at Orica Kooragang Island and Yarwun, the ammonium-nitrate plants at Yara Pilbara Nitrates Karratha and Dyno Nobel Moranbah, the fertiliser sites at Incitec Pivot Phosphate Hill, Geelong and Gibson Island and CSBP Kwinana, the herbicide formulators at Nufarm Laverton, Adama Australia, Sumitomo Chemical Australia and BASF Australia, the polymer legacy at Qenos Botany and Altona (the ethylene cracker closed in 2024), Quantam Plastics and LyondellBasell Australia, and the industrial-gas footprint of Air Liquide Australia at Bayswater and Yennora, BOC Australia (Linde plc) at Bulwer Island, Coregas at Yennora and Supagas. It is also relevant to the lubricant blending at Castrol BP, Penrite Heatherton and Hi-Tec Oils, the Shell Geelong and Caltex Lytton hand-offs, the helium import logistics of Iwatani Australia, and the proposed Murray Methanol facility.

The recurring failure mode we see in the field is the same one we see in pharma and cleanrooms — somebody specifies galvanised duct, and three years later the maintenance team is welding patch plates over perforated zinc skin while the EHS lead is filing an incident report on fugitive emissions. The difference in a chemistry building is that the fugitive emission is not a stray dust particle — it is methanol vapour into a Zone 1 envelope, ammonia at 30 ppm into a control room, or chlorine creeping along a roof void at the back of a herbicide tank farm. The cost of getting the metallurgy wrong is not a service call — it is a notifiable incident.

The Australian regulatory frame

Australian chemical manufacturing sits inside a stacked set of regulatory instruments. Each one imposes design obligations on the HVAC scope, and skipping any of them produces a non-compliant building that will not survive an audit. What is specifically Australian is the federation structure — the Work Health and Safety Act is national but implemented through state regulations, Major Hazard Facility licensing is a state instrument, and the dangerous-goods transport regime is the Australian Dangerous Goods Code (ADG 7.9). The applicable technical standards layer on top.

AS/NZS 60079 — Hazardous areas

AS/NZS 60079.10.1 classifies areas where flammable gas or vapour may be present, and AS/NZS 60079.10.2 classifies areas where combustible dust may be present. The classification produces zones — Zone 0 where an explosive atmosphere is continuously present, Zone 1 where it is likely to be present in normal operation, and Zone 2 where it is unlikely and only present briefly. Dust zones are numbered Zone 20, Zone 21 and Zone 22 in the same hierarchy. Each zone drives the equipment protection level (EPL) and ignition-protection type (Ex d, Ex e, Ex i, Ex n, Ex t for dust) of every electrical device inside the envelope. The ductwork itself is passive but everything attached to it — fans, motors, dampers, smoke detectors, gas sensors, junction boxes, lights, position transmitters — has to be IECEx- or ATEX-certified to match the zone. Earthing continuity across every duct joint becomes a design requirement in Zone 1 and Zone 2 because the metal duct is itself a potential static-discharge source where powder, mist or vapour is in suspension.

AS 1940 — Storage and handling of flammable and combustible liquids

AS 1940 covers the storage and handling of liquids classified under the ADG Code as Class 3 flammable or as combustible. The standard prescribes building construction, separation distances, bunding, electrical area classification (cross-referenced into AS/NZS 60079) and — relevantly to this guide — mechanical ventilation requirements for indoor storage. Indoor flammable-liquid storage rooms typically design to 5 to 12 air changes per hour on normal mode and 30 air changes per hour on emergency mode, with the emergency mode triggered by LEL gas detection at 20 percent of the lower explosive limit. The ventilation is normally an extract-only system with fresh air drawn through louvres, so that the room runs at slight negative pressure relative to surrounding spaces and any leak migrates out through the extract rather than through the door. The fan and any in-duct damper inside the AS 1940 envelope is Zone 1 or Zone 2 rated under AS/NZS 60079, and the duct itself has to handle the chemistry of the stored product — for solvent stores with mixed chemistry that almost always means 316L stainless.

AS 4332 — Storage and handling of gases in cylinders

AS 4332 is the Australian standard for cylinder-gas storage including industrial gases such as oxygen, hydrogen, nitrogen, argon, helium, acetylene and refrigerants, and toxic or corrosive gases such as chlorine, sulphur dioxide, ammonia and ethylene oxide. The standard sets out segregation rules between incompatible cylinders, fire-protection requirements and ventilation. Cylinder-gas store rooms inside a building have to be mechanically ventilated to prevent accumulation of leaked gas, typically at 6 to 10 air changes per hour on normal operation and stepped up to 25 to 30 air changes per hour on detection of a toxic gas above its short-term exposure limit (STEL) or a flammable gas above 20 percent LEL. For Air Liquide Australia, BOC Australia, Coregas and Supagas filling stations and depot rooms, AS 4332 is the operating standard, and the duct material is selected to match the worst-case gas chemistry — stainless for chlorine and SO₂ rooms, galvanised acceptable for pure-inert-gas (nitrogen, argon) storage where chemistry is benign.

AS 3780 — Storage and handling of corrosive substances

AS 3780 covers Class 8 corrosive substances under the ADG Code — sulphuric, hydrochloric, nitric, phosphoric and hydrofluoric acids, sodium hydroxide, ammonia solution, and a long tail of process chemicals. Storage rooms are mechanically ventilated to prevent accumulation of fume and to maintain breathable atmosphere in adjacent occupied spaces. The standard prescribes that ventilation system materials in contact with the air stream are compatible with the substances stored — which in plain English means galvanised steel is non-compliant for the extract serving any reasonable mix of Class 8 corrosives, and the default specification becomes 316L stainless, FRP, polypropylene-lined steel or PVDF depending on the specific chemistry.

AS 1668.2 — Mechanical ventilation in buildings

AS 1668.2 is the umbrella mechanical-ventilation code for Australian buildings and provides the base methodology for sizing outside-air, exhaust and recirculated-air systems. For industrial chemical-process buildings the code points outward to the specific hazardous-substance standards (AS 1940, AS 4332, AS 3780) for the design rates and falls back to general industrial occupancy rates of 6 to 12 air changes per hour where no specific standard governs. AS 1668.2 is also the reference for kitchen and process-exhaust calculations in plant-room amenities, control-room HVAC and warehouse comfort cooling — the parts of a chemical site that look like ordinary commercial HVAC.

NFPA 30 and NFPA 484

NFPA 30 (Flammable and Combustible Liquids) and NFPA 484 (Combustible Metals and Metal Dust) are US standards widely adopted by reference in Australian Safety Cases for parent-company alignment. NFPA 30 closely tracks AS 1940 but is more prescriptive on tank-vent piping and inerting. NFPA 484 governs combustible-metal dust — relevant for any site processing aluminium, magnesium, titanium or lithium powders (an increasingly important battery-precursor category in Australia). Where NFPA 484 applies the duct carries explosible dust and the design incorporates deflagration venting, anti-static internal lining, isolation valves and explosion isolation, with fan and motor rated for the dust zone.

API RP 752 and API 521

API RP 752 (Management of Hazards Associated with Location of Process Plant Permanent Buildings) is the American Petroleum Institute recommended practice for building siting in petrochemical and refining plants — it is the standard used to demonstrate that occupied buildings are sited far enough from process units to survive a credible release event or pressure wave. It does not prescribe ductwork specifications directly but it constrains where HVAC fresh-air intakes can be located. Intakes have to be placed so that a credible flammable-vapour cloud cannot be drawn into the building, which usually means high-level intakes on the side furthest from the process area and overpressure dampers wired through the gas-detection system. API 521 (Pressure-Relieving and Depressuring Systems) governs the flare and vent header design — relevant to HVAC because relief streams discharged at low level under fault conditions can flood the HVAC intake of an adjacent control room.

COMAH, SEVESO III and the Australian MHF regime

Europe regulates Major Hazard sites under SEVESO III (the directive) and COMAH (the UK implementation). Australia has its own equivalent — the Major Hazard Facility cohort, licensed under the state implementations of the model Work Health and Safety Act and regulations. A site is an MHF if it stores or handles Schedule 15 dangerous goods above a threshold quantity — for example more than 200 tonnes of ammonium nitrate, more than 50 tonnes of liquid chlorine, more than 200 tonnes of LPG, or various amounts of other Schedule 15 items. MHF status triggers a Safety Case obligation — the operator has to demonstrate to the regulator that all reasonably practicable controls are in place to prevent and mitigate a Major Incident. The Safety Case becomes the design envelope for every system on site, including HVAC. Bow-tie analyses for credible scenarios — toxic release, flammable-vapour ignition, dust explosion, runaway reaction, tank rupture — name the ventilation system as a layer of protection in many cases, which converts ductwork from a comfort item to a safety-critical item with documentation, inspection and change-management obligations to match.

Australian Dangerous Goods Code (ADG 7.9)

ADG 7.9 is the Australian Dangerous Goods Code, currently at edition 7.9, and it harmonises Australia with the UN Recommendations on the Transport of Dangerous Goods. ADG governs labelling, packaging, classification and transport — but it also feeds back into the static storage standards because the substance classes (Class 2 gases, Class 3 flammable liquids, Class 5.1 oxidisers including ammonium nitrate, Class 6 toxic, Class 8 corrosive) drive which static-storage standard applies. The HVAC design report for any chemical site should reference the ADG classification of every stored substance so the auditor can trace the storage layout back to the regulatory frame.

The Australian chemical industry map

Before specifying ductwork the engineer needs a clear picture of the actual industry — who is making what, where, and which buildings need ventilation. The following is a working map of the major chemical manufacturers operating in Australia in 2026.

Explosives manufacturing

Australian explosives manufacturing is dominated by three players. Orica is the largest, with the Kooragang Island ammonium-nitrate, ammonia and explosives precinct in Newcastle NSW and the Yarwun ammonium-nitrate site in Gladstone QLD. Dyno Nobel operates the Moranbah ammonium-nitrate plant in central Queensland and a network of regional explosives works. Maxam Australia operates explosives manufacturing and distribution into the mining sector. All three operate Major Hazard Facility licensed sites and all three have Safety Cases that name the HVAC system as a layer of protection in their bow-tie analyses for ammonia release, ammonium-nitrate decomposition and packaged-explosive thermal initiation. The ductwork inside an ammonium-nitrate prill tower or pastillation building has to handle hot moist air laden with nitric oxides — 316L stainless is the minimum and Hastelloy is used in localised high-temperature high-acid zones. Cross-reference the mining mineral processing and smelter HVAC duct guide for the downstream blast-hole loading and bulk-emulsion side.

Ammonium nitrate and ammonia

Ammonium nitrate is the load-bearing molecule for both the explosives industry (as ANFO and emulsion oxidiser) and the fertiliser industry (as a high-N fertiliser and as a precursor for compound fertilisers). Major Australian producers include Orica at Kooragang Island and Yarwun, Yara Pilbara Nitrates at Karratha WA (the Burrup Peninsula technical-grade ammonium-nitrate plant), and Dyno Nobel Moranbah. The Yara Pilbara complex also includes Yara Pilbara Fertilisers, the ammonia plant that feeds the nitrate plant and exports merchant ammonia. Ammonia ventilation in these facilities is the central HVAC design challenge — ammonia is toxic above 25 ppm STEL and explosive between 15 and 28 percent by volume in air. Compressor halls, ammonia transfer corridors and packaging halls run on a normal-mode 8 to 12 ACH and step up to 25 to 30 ACH on ammonia detection above 25 ppm. Duct material is 316L stainless throughout — ammonia is a strong alkali in solution with atmospheric moisture and consumes zinc rapidly.

Fertilisers

The Australian fertiliser industry is built around four operators. Incitec Pivot operates Phosphate Hill in north-west QLD (the only Australian integrated phosphate-rock-to-DAP plant), Geelong in VIC (single super-phosphate and sulphuric acid), and Gibson Island in Brisbane (urea and ammonia, formerly a major producer, with a hydrogen transition under evaluation). Yara Pilbara at Karratha WA produces merchant ammonia and technical ammonium nitrate. CSBP, the chemicals arm of Wesfarmers, operates the Kwinana WA site producing ammonium nitrate, ammonia, sodium cyanide and a portfolio of mining and agricultural chemicals. Sulphuric-acid plants on these sites are the high-corrosion HVAC challenge — process bays venting hot acid mist need 316L or higher and the regenerative-tower fans are typically Hastelloy-clad. Urea prilling and DAP granulation towers are dust-handling environments under AS/NZS 60079.10.2 — Zone 22 internally and Zone 21 on the discharge.

Agrochemicals

Crop-protection formulation in Australia is a smaller but more diverse industry than the bulk inorganics. The largest local manufacturer is Nufarm Australia at Laverton VIC, with a herbicide and adjuvant portfolio that serves grain, horticulture and broadacre agriculture. Adama Australia formulates and distributes a broad crop-protection portfolio. Sumitomo Chemical Australia and BASF Australia operate formulation, distribution and warehousing into the Australian agricultural market. Agrochemical formulation buildings handle a mixed bag of solvents (xylene, toluene, white spirits, glycol ethers), wetting agents and active ingredients — many of which are toxic, flammable, or both. The HVAC design challenge is that the building hosts AS 1940 flammable-liquid storage in one corner, AS 3780 corrosive storage in another, AS 4332 cylinder storage in a third and an active formulation hall in the middle. Each area has its own ventilation rate, hazardous-area zoning and material specification, and the duct network has to keep them aerodynamically isolated through interlocked dampers and pressure cascade.

Polymers and plastics

Australian polymer manufacturing has contracted over the past decade. Qenos, the joint-venture operator of the Botany NSW ethylene plant and the Altona VIC polyethylene plant, closed its Australian production in 2024 — ending domestic ethylene cracking and primary polyethylene manufacture. The downstream polymer-conversion industry continues, with Quantam Plastics, LyondellBasell Australia (technical and distribution presence) and a long tail of compounders, masterbatch producers, pipe extruders, blow moulders and rotational moulders. The HVAC scope for polymer conversion is dominated by hot-melt fume extraction, monomer-residual venting and dust-handling for additive blending. The dust side falls under AS/NZS 60079.10.2 Zone 22 and frequently NFPA 484 where reactive metal pigments are blended.

Industrial gases

The Australian industrial-gas industry is dominated by four operators. Air Liquide Australia operates the Bayswater VIC and Yennora NSW air-separation plants and a national filling and distribution network. BOC Australia, part of Linde plc, operates the Bulwer Island QLD air-separation plant and a network of branches. Coregas, owned by Wesfarmers, operates the Yennora NSW facility and distributes nationally. Supagas operates a network of filling and distribution sites. Helium is imported into Australia under merchant agreements — Iwatani Australia is a major importer through Sydney and Melbourne. Air-separation plants produce oxygen, nitrogen and argon at cryogenic temperature through fractional distillation; cold-box buildings around the distillation columns require very stable internal temperature and humidity, while the warm-end compressor halls run at high-temperature, high-noise and high air-change rates. Filling stations under AS 4332 ventilation rates handle a portfolio of inert, oxidising, flammable and toxic gases — the duct material is selected per filling bay to match the gas chemistry. Cross-reference the hydrogen production HVAC duct guide for the hydrogen and ammonia side, and the LNG and natural gas processing HVAC duct guide for cryogenic upstream parallels.

Methanol

Australia has historically been a methanol importer rather than a producer. The proposed Murray Methanol project in the Pilbara has been under feasibility evaluation for natural-gas-to-methanol and may move to FEED. If built, it adds another major Class 3 flammable-liquid handler to the Australian chemical map with associated AS 1940 storage and AS/NZS 60079 hazardous-area HVAC scope.

Lubricants and base oils

The Australian downstream-petroleum industry has been through significant consolidation. The Caltex Lytton refinery (Brisbane) was closed and converted to import terminal operation. The Shell Geelong refinery was acquired by Viva Energy and is the last remaining domestic refinery on the east coast. Castrol BP operates lubricant blending in Australia. Penrite Oil operates the Heatherton VIC blending plant. Hi-Tec Oils operates blending operations in regional NSW. Blending plants handle base oils, additives and finished lubricants — the HVAC scope is dominated by mist extraction over the blending vessels, AS 1940 flammable-storage ventilation for solvent-based additives and AS 3780 corrosive ventilation for the small inventory of acid neutralisers and viscosity modifiers.

Why galvanised duct fails in chemistry buildings

Almost every newcomer to chemical HVAC starts with the wrong assumption — that galvanised steel duct, which works perfectly well in commercial buildings, schools, hospitals and warehouses, can be patched into a chemical plant by being thicker or by being painted. It cannot, and the reason is metallurgical rather than thickness-based.

Galvanised steel is carbon steel coated with a layer of zinc — typically Z275 (275 g/m² zinc-coated both sides) for HVAC duct stock. Zinc is sacrificial — it corrodes preferentially to protect the underlying steel, because zinc is anodic to iron in the galvanic series. In an indoor air environment the zinc oxidises slowly to form a protective passive layer (zinc carbonate and hydroxide) that arrests further corrosion. In a chemistry environment the passive layer is consumed by acid attack, alkali dissolution or solvent disruption, and once it is gone the bare zinc corrodes at full speed until it is gone too. The exposed carbon steel then rusts uncontrollably.

The four mechanisms that destroy galvanised duct in a chemical plant are:

1. Acid attack. Mineral and organic acids (sulphuric, hydrochloric, nitric, acetic, formic) react with zinc to form soluble zinc salts. Aerosols and condensate of any concentration above trace levels consume the zinc within months.
2. Alkali attack. Strong alkalis (sodium hydroxide, ammonia solution, potassium hydroxide) dissolve zinc to form soluble zincates. Ammonia is particularly aggressive because it forms zinc-amine complexes that go into solution even at neutral pH.
3. Solvent disruption. Organic solvents (toluene, xylene, methyl ethyl ketone, isopropyl alcohol) do not attack zinc directly but they wet the surface and prevent the passive layer from forming. When solvent vapour cycles in and out of the duct the zinc surface sees fresh oxidative attack each cycle.
4. Heat acceleration. Every 10°C increase in surface temperature approximately doubles the rate of corrosion reaction. Hot extract from a sulphuric-acid plant, a urea prill tower or a phosphoric-acid evaporator amplifies the chemistry above by an order of magnitude.

The end state is duct perforation, uncontrolled fugitive emission into the workshop, immediate breach of AS 3780 and AS 1940 ventilation-integrity requirements, immediate breach of the Major Hazard Facility Safety Case where one applies, and a probable improvement-or-prohibition notice from the state regulator. The fix is to specify the right metallurgy at design and never let a galvanised section past the drawing review.

Stainless 316L — the chemical HVAC default

The default material for primary process-extract and process-supply ductwork in Australian chemical plants is austenitic stainless steel grade 316L. The L stands for low-carbon (≤0.03 percent carbon) — the low-carbon variant resists sensitisation and intergranular corrosion in the heat-affected zone after welding, which matters because every joint in a TIG-welded chemical duct is a welded joint. Standard 316 with 0.08 percent carbon is acceptable for short ducts that do not need welding-grade corrosion resistance, but for full-shop-fabricated welded systems 316L is the sensible default.

The relevant 316L chemistry is approximately 17 percent chromium, 12 percent nickel and 2.5 percent molybdenum, with the rest iron. The chromium forms the passive chromium-oxide layer that protects the underlying alloy; the nickel stabilises the austenitic phase; the molybdenum gives the alloy its resistance to chloride pitting, which is the dominant failure mechanism of the cheaper 304 stainless in coastal and chloride-rich environments. Most Australian chemical sites are coastal or near-coastal (Kooragang Island, Yarwun, Karratha, Kwinana, Bulwer Island, Yennora, Bayswater) and the chloride loading from sea spray alone is enough to drive a switch from 304 to 316L. Once 316L is on the drawing, it survives almost everything chemistry can throw at it short of strong halogen acids at temperature.

For SBKJ-fabricated 316L duct the standard configuration is full-thickness 316L sheet stock (1.2 mm minimum for low-pressure extract, 1.6 mm or 2.0 mm for process-extract and any duct downstream of a fan), longitudinal seams TIG-welded with 316L filler metal, transverse joints either TIG-welded butt joints or 316L flanged joints with chemically compatible gaskets (EPDM, Viton or PTFE depending on chemistry). Internally the duct is passivated after welding with a citric or nitric pickle to restore the chromium-oxide layer in the heat-affected zone. The result is a duct that lasts 25 to 40 years in service — longer than the building.

Hastelloy and Inconel — the upgrade alloys

316L is not the answer for everything. The two scenarios where it fails are halogen-acid attack at temperature (hot hydrochloric or hydrobromic acid mist, hot wet chlorine) and very high temperature service above 600°C. The upgrade path is to nickel-base superalloys — Hastelloy C-276, Hastelloy C-22, Inconel 625 — fabricated as either solid alloy duct sections or as alloy-clad carbon steel for cost optimisation.

Hastelloy C-276 is the workhorse in halogen-acid service. The alloy is approximately 16 percent chromium, 16 percent molybdenum and 4 percent tungsten in a nickel matrix, and it resists wet chlorine, hypochlorite, hydrochloric acid and hydrobromic acid at temperature where 316L pits within months. The Australian use case is in chloralkali plants (now small — the Australian chloralkali capacity is concentrated at the Tas chlorine plant and the historical Botany chlorine plant that wound down), in agrochemical formulators handling chlorinated intermediates, and in localised high-acid bay extracts at the inorganic-fertiliser sites.

Inconel 625 is the upgrade for high-temperature oxidising service — flue-gas ducts, hot-acid plant extracts and incinerator stacks. The alloy keeps mechanical properties to about 800°C and resists oxidation by hot acidic gases. In the Australian chemical industry Inconel 625 shows up most often as cladding on stack and duct sections downstream of sulphuric-acid converter beds and on the tail-gas side of nitric-acid plants.

The procurement reality is that Hastelloy and Inconel cost roughly five to eight times the equivalent 316L on a per-tonne basis, so the right approach is to map the duct network bay-by-bay and use 316L for general service with localised Hastelloy or Inconel inserts at the high-corrosion nodes — not to blanket the whole site in superalloy.

FRP and polypropylene-lined steel — the acid-only option

For purely acid streams without solvent contamination, fibre-reinforced plastic (FRP) duct and polypropylene-lined carbon steel duct are valid alternatives to 316L stainless. FRP — typically a vinyl-ester or isophthalic-polyester resin reinforced with chopped or woven glass fibre — is widely used on chemical sites in Australia for sulphuric-acid plant fume extracts, electroplating fume extracts and battery-acid handling. The advantages are dramatically lower capital cost than 316L (roughly 40 to 60 percent depending on diameter) and excellent resistance to mineral-acid attack without the chloride-pitting risk of stainless. The disadvantages are limited temperature service (FRP softens above approximately 100°C continuous), low resistance to organic solvents (which dissolve or swell the resin), and a long lead time on bespoke fabrication that does not fit a fast-track shop schedule.

Polypropylene-lined carbon steel is a hybrid — a structural carbon-steel outer shell with a polypropylene inner liner that contacts the air stream. It combines the structural advantages of steel duct (long spans, easy support, lower bracing density) with the chemistry advantages of polypropylene (resistance to mineral acids and alkalis at moderate temperature). Both FRP and PP-lined are non-conductive, which becomes a design issue in Zone 1 and Zone 2 envelopes — an FRP duct cannot dissipate static and so it has to be either fully bonded with an internal conductive grid or specified as non-acceptable for the hazardous zone. In practice FRP and PP-lined ducts are used in non-hazardous chemical service (acid plants outside the explosion envelope) and 316L stainless is used in the hazardous zones.

ATEX, IECEx and AS/NZS 60079 — the hazardous-zone constraint

Inside any zone identified under AS/NZS 60079.10.1 or 60079.10.2 every piece of electrical equipment must be certified to the equipment protection level required for the zone, by the protection technique listed for that EPL. For Australia the certification regime is IECEx — the international scheme that is accepted in Australia via AS/NZS 60079. The European ATEX scheme is functionally equivalent and ATEX-marked equipment from a Notified Body is widely accepted with appropriate paperwork. For HVAC inside a hazardous zone the equipment lists are:

• Fans — Ex d (flameproof enclosure) or Ex e (increased safety) motors for Zone 1; Ex nA, Ex nC for Zone 2; Ex t (dust ignition protection by enclosure) for Zone 21 and Zone 22. The impeller and casing also need to be designed to prevent sparking from rotor-to-stator contact under fault — non-sparking impellers in aluminium-bronze or stainless are typical.
• Dampers — actuators must match the zone, and damper spindles need bonding straps across the actuator-blade interface for static dissipation in dust-bearing service.
• Sensors — pressure, temperature, gas detection, smoke detection, position feedback — every one of these has to be certified for the zone and connected through Ex-rated cable glands and junction boxes.
• Lights and accessories — duct-mounted inspection lights, sight-glass illumination, junction boxes — all certified to zone.
• Earthing — every duct joint inside Zone 1 and Zone 2 must have continuity verified by testing, and flexible connectors need bonding straps across the flex. The duct itself becomes an earthed enclosure; it does not need certification but it must be electrically continuous and bonded to the site earth.

SBKJ supplies hazardous-area ductwork with the AS/NZS 60079 and IECEx option — duct delivered with continuity-tested earthing across every joint, anti-static internal lining where specified, and a fan-and-damper package sourced from IECEx-listed brands matched to the zone.

Emergency ventilation — 25 to 30 ACH on gas detection

The single most important active HVAC feature of a chemical-process building is its emergency ventilation regime. In normal operation the building runs at 6 to 12 air changes per hour for occupant comfort, dilution of trace fugitive emission and removal of heat from process equipment. In an emergency — defined by gas detection above an alarm threshold — the ventilation steps up to 25 to 30 air changes per hour to dilute the released material below its toxic or flammable limit before it can do harm.

The triggers for emergency-mode ventilation are typically:

• Flammable gas at 20 percent LEL — for flammable-vapour areas under AS 1940, the trigger is 20 percent of the lower explosive limit measured by a catalytic-bead or infrared sensor. At 20 percent LEL the building dampers step to extract-only and the extract fan steps up to high-speed.
• Toxic gas at the short-term exposure limit (STEL) — for chlorine, ammonia, hydrogen sulphide, sulphur dioxide and similar toxic gases, detection above the STEL (typically 1 to 25 ppm depending on the substance) triggers emergency extract and isolates supply to non-affected zones.
• Oxygen depletion below 19.5 percent — for inert-gas areas (nitrogen and argon filling, cryogenic plant) detection below 19.5 percent oxygen triggers emergency ventilation to restore breathable atmosphere before personnel are exposed.
• Manual emergency-mode initiation — a hard-wired emergency button at the area entrance triggers the same response without waiting for a gas detector.

The design data point is that the extract fan must be capable of 25 to 30 ACH on demand, which means it is sized for emergency mode and throttled in normal mode through a variable-speed drive or two-speed motor. The supply system runs at full fresh-air on emergency (no recirculation, no economy) and dampers in interconnecting ducts close to isolate non-affected zones from the affected zone. The whole sequence is documented in the building cause-and-effect matrix and validated at commissioning by witnessing the response to a simulated gas-detector trip.

Acoustic design — NC-55 industrial

Chemical-process areas are not quiet. Compressor halls, prill towers, granulation drums and air-separation cold boxes all sit in the NC-55 to NC-65 acoustic envelope (background sound levels around 60 to 70 dBA). The HVAC acoustic challenge is to keep the duct system from making the noise problem worse, not to make the process bay quiet — that requires acoustic enclosure of the noise source which is outside the HVAC scope. The relevant HVAC acoustic specifications are:

• Process bays — design to NC-55 from HVAC alone (combined with the process noise the bay sits in NC-65 territory).
• Control rooms — design to NC-35 with attenuators on supply and return ducts entering the room from the process side. Control rooms must also satisfy the API RP 752 blast-overpressure resilience requirement, which means the HVAC penetrations through the blast-rated wall need blast-rated dampers and bellows.
• Plant-room amenities — design to NC-40 by AS 1668.2 baseline.

The metallurgy constraint affects attenuator selection. A standard galvanised splitter attenuator with mineral-wool acoustic infill survives in office HVAC but corrodes out of service within a year in an agrochemical formulation room. The right specification for chemical HVAC is a 316L stainless attenuator with an acoustically transparent perforated stainless face and a stainless-encapsulated acoustic infill — or, where 316L attenuators are not commercially available in the required performance, a custom-fabricated stainless attenuator delivered by the SBKJ shop alongside the duct.

SBKJ machine configuration for chemical-grade ductwork

Fabricating chemical-grade ductwork at the scale required by Australian projects — typically 80 to 250 metres of run per process building, with 30 to 60 percent of joints welded — requires the right shop equipment. The SBKJ standard machine configuration for chemical-industry fabrication shops is:

• SBAL-V stainless 316L auto duct line — the SBAL-V is the stainless variant of the SBAL auto duct line, configured with 316L-compatible tooling, full TIG-welded longitudinal seam closure and a coil de-coiler and leveller sized for 316L sheet stock at 1.2 mm to 2.0 mm thickness. The line produces rectangular duct sections at TDF or PB flange standard with consistent dimensional tolerances meeting AS/NZS 4254 and SMACNA. For chemical-plant projects the SBAL-V is typically configured with a stainless plasma cutter for the slot-and-tab transverse joint and a notch-and-bend station for the TDF flange profile.
• SBTF-2020 spiral tubeformer with stainless tooling — the SBTF-2020 is SBKJ's spiral tubeformer, configured for 316L stainless production from 80 mm to 2000 mm diameter. Spiral round duct is the preferred geometry for chemical-process extract because it is structurally efficient, easy to seal and minimises particulate accumulation at internal seams. The stainless tooling option uses tungsten-carbide rollers and a stainless-compatible forming geometry to avoid iron contamination of the duct surface.
• TIG seam welder — manual and automated TIG welding stations for closing longitudinal seams, butt joints and branch connections to weld procedure specifications consistent with AS/NZS 1554.6 (welding of stainless steels) and the relevant ASME Section IX procedure references where parent-company alignment requires it.
• AS/NZS 60079, ATEX and IECEx fabrication-shop option — where the fabrication shop itself is classified as a Zone 22 dust-handling area (because of stainless-steel grinding swarf), the SBKJ machine line is configured with hazardous-area-rated electrical components, anti-static drive belts and bonded earthing throughout. This is a less common shop configuration but it is the right one for fabrication shops that operate inside an existing chemical-site footprint.

Cross-reference the SBKJ machine catalogue for full specification, output and certification details, and the 47-point HVAC duct machine buyer's checklist for the procurement verification questions to ask any vendor — SBKJ or otherwise.

Worked example — herbicide formulator at Laverton

To make the design discussion concrete, here is a notional agrochemical formulation plant in the Laverton industrial precinct in Melbourne's west, sized at 12,000 tonnes per annum of formulated herbicide product blending xylene-based solvent carriers with glyphosate, 2,4-D and a portfolio of post-emergent herbicides. The site sits above the threshold for aggregate flammable-liquid storage and is regulated as an MHF under the Victorian Occupational Health and Safety (Major Hazard Facilities) Regulations. The building has six functional zones:

• Zone A — bulk solvent storage. AS 1940 indoor flammable-liquid storage. AS/NZS 60079 Zone 1 above the tanks, Zone 2 at the room boundary. 5 ACH normal, 30 ACH emergency on LEL detection. 316L stainless with TIG-welded seams, Zone 1 IECEx-rated fan and dampers, continuous bonding and earthing.
• Zone B — corrosive storage. AS 3780 storage of sulphuric, hydrochloric, sodium hydroxide and ammonia solution. 6 ACH normal, 20 ACH on hydrogen-chloride detection. FRP vinyl-ester on extract, 316L on supply because of coastal chloride loading.
• Zone C — cylinder gas storage. AS 4332 nitrogen and chlorine cylinders. Zone 2 around the chlorine bay. 6 ACH normal, 25 ACH on chlorine at 1 ppm. 316L on chlorine extract, galvanised acceptable on nitrogen supply.
• Zone D — formulation hall. Solvent, surfactant and active ingredient blended in stainless vessels. Zone 2 above the vessels. 10 ACH normal, 25 ACH emergency. 316L throughout with stainless NC-55 attenuators.
• Zone E — packaging hall. Filling from 5 L jerry cans to 1000 L IBC with local-extract hoods over each filling point. 316L on local extract, galvanised on general supply.
• Zone F — warehouse and dispatch. Non-hazardous, galvanised HVAC at AS 1668.2 default rate, segregated from process areas by vapour-tight wall.

Total scope is approximately 180 metres of 316L stainless extract, 40 metres of FRP corrosive extract, 60 metres of 316L stainless supply and 90 metres of galvanised general supply and warehouse, with 4 hazardous-area-rated extract fans, 12 zone-rated isolation dampers and 18 gas detectors in a cause-and-effect matrix. SBKJ fabricates this scope with the SBAL-V stainless auto duct line, the SBTF-2020 spiral tubeformer, a TIG seam welder and an FRP sub-contract for the corrosive section. Total fabrication is approximately eight weeks single-shift.

Worked example — air-separation cold box at Bayswater

The second worked example is the air-separation plant — the technology behind every industrial-gas producer in Australia (Air Liquide at Bayswater and Yennora, BOC at Bulwer Island, Coregas at Yennora). Air-separation plants compress ambient air, cool it to cryogenic temperature and fractionally distil it into oxygen, nitrogen and argon. The HVAC scope splits cleanly into three:

• Cold-box building. The cold-box is an insulated enclosure around the cryogenic distillation columns. Internal HVAC maintains stable temperature and humidity around the cold-box to prevent moisture migration into the perlite insulation. 8 ACH normal, 25 ACH on oxygen-depletion below 19.5 percent or enrichment above 23.5 percent. Galvanised acceptable because the air is dry and benign.
• Compressor hall. Air and refrigeration compressors driving the cycle. High-temperature, high-noise — 12 to 20 ACH. NC-65 in the hall, NC-35 in the adjoining control room. Galvanised on supply, galvanised or 316L on extract depending on lubricant carry-over.
• Filling station and gas storage. AS 4332 governs the layout. Oxygen filling areas are oxygen-enrichment hazards — 316L stainless with oil-free internals and no aluminium in the air stream. Nitrogen and argon filling are oxygen-depletion hazards. 8 ACH normal, 25 ACH on oxygen detection out of range.

The metallurgy lesson is that 316L is required for oxygen service (cleanliness and ignition resistance) but not for cold-box and compressor halls. Sites that blanket the whole plant in stainless overspend by roughly 40 percent on duct material; sites that blanket the whole plant in galvanised end up retrofitting the oxygen station within five years.

Worked example — ammonium-nitrate prill tower at Kooragang Island

The third worked example is the high-end of the chemical HVAC envelope — an ammonium-nitrate prill building at an MHF-licensed site, loosely modelled on the Orica Kooragang Island precinct in Newcastle. The prill tower sprays molten ammonium-nitrate solution at approximately 180°C through a head at the top of a 50 to 70 metre tower; droplets solidify into prills as they fall through a counter-current of cooling air, which exhausts at the top carrying nitric-oxide fumes, fine ammonium-nitrate dust and trace ammonia. The HVAC scope:

• Prill tower stack and cyclone. 316L stainless on the cyclone inlet and outlet, Hastelloy C-22 cladding on localised high-temperature high-acid zones, full external lagging to prevent structural steel from seeing condensate.
• Building general ventilation. Slight negative pressure to prevent fugitive dust escape. 8 ACH normal, 25 ACH on ammonia or NOx detection above STEL. 316L stainless throughout because of coastal chloride loading.
• Hazardous-area dust zones. Prill packaging and bagging is AS/NZS 60079.10.2 Zone 22 (locally Zone 21 above the bagging machine). Fans and damper actuators Ex t certified; duct continuously bonded and earthed with anti-static internal lining over the bagging bay.
• Control room. Blast-rated per API RP 752 because the site stores molten ammonium-nitrate above threshold, with blast-rated dampers on every HVAC penetration and a positive-pressure regime to keep ammonia, NOx and dust out.

Total scope is approximately 240 metres of 316L stainless duct, 30 metres of Hastelloy C-22 cladded transitions, 6 hazardous-area-rated extract fans and 18 zone-rated dampers. SBKJ delivers this through an SBAL-V stainless auto duct line, an SBTF-2020 spiral tubeformer, a TIG seam welder and a Hastelloy-clad sub-contract for the transition pieces.

Project sequencing and lead time

Chemical-industry HVAC projects sit on long lead times because of the metallurgy, the certification stack and the project documentation burden. A representative schedule for a single chemical-process building from design freeze to first article fabricated is:

• Weeks 1 to 4 — Design and hazard freeze. Hazardous-area classification drawing signed off, dangerous-goods register complete, Safety Case extracts referenced, AS/NZS code applicability matrix complete, single-line ventilation drawing signed off.
• Weeks 4 to 8 — Procurement and material lead. 316L stainless sheet stock ordered to project schedule (lead time 6 to 10 weeks from mill for project tonnages), Hastelloy or Inconel ordered (lead time 14 to 22 weeks from specialist mill), IECEx fan-and-damper package ordered (lead time 12 to 20 weeks from specialist supplier).
• Weeks 8 to 16 — Fabrication. SBAL-V stainless auto duct line single-shift output is approximately 2,500 m² of duct per week at chemical-grade thickness; the worked example herbicide formulator scope of 280 metres total fabricates in roughly four weeks of shop time. Quality records (welder qualifications, weld procedure specifications, root and visual inspection records, mill certificates for the 316L sheet stock) are compiled in parallel.
• Weeks 16 to 20 — Shipment and site delivery. 316L stainless duct shipped flat-packed for site assembly; pre-fabricated welded sections shipped in protective crating with ISPM-15 fumigation stamp and humidity indicators.
• Weeks 20 to 28 — Site assembly, hazardous-area continuity testing, gas-detection commissioning, cause-and-effect matrix witness testing.
• Weeks 28 to 32 — Documentation hand-over to the operator EHS and regulatory audit.

The single most common schedule risk is under-ordering the IECEx fan-and-damper package — the specialist suppliers have 12 to 20 week lead times and stockholding is thin for the larger sizes. Ordering the fans on day one of the project, in parallel with the duct, is the discipline that keeps the schedule from slipping at week 16.

Cost envelope

A representative cost envelope for chemical-industry ductwork in 2026 prices (Australian dollars, ex-works fabrication shop, before site installation and commissioning):

• Galvanised steel duct — AUD 60 to AUD 110 per square metre installed, for non-hazardous office and warehouse areas physically segregated from process.
• 316L stainless duct, TIG-welded — AUD 320 to AUD 580 per square metre installed, for general chemical-process extract and supply.
• FRP vinyl-ester duct — AUD 180 to AUD 340 per square metre installed, for cold acid streams without solvent contamination.
• Polypropylene-lined carbon steel — AUD 240 to AUD 420 per square metre installed, for mineral-acid streams at moderate temperature.
• Hastelloy C-276 or C-22 clad duct — AUD 1,800 to AUD 3,200 per square metre installed, for halogen-acid and high-temperature acid service.
• Inconel 625 clad duct — AUD 2,400 to AUD 4,800 per square metre installed, for hot oxidising and high-temperature acid gas service.

The cost case for designing the network bay-by-bay rather than blanketing the whole project in one alloy is straightforward — the difference between specifying 316L throughout a 1,000 m² duct envelope (AUD 320,000 to AUD 580,000) and specifying 316L for 70 percent and FRP for 30 percent (AUD 224,000 stainless plus AUD 102,000 FRP, total AUD 326,000) is roughly AUD 100,000 to AUD 250,000 of saved capital at no compromise in performance. The cost case for designing in galvanised where chemistry permits is even larger — replacing galvanised with stainless on a 200 m² non-hazardous warehouse and amenities run wastes about AUD 50,000 per project.

Documentation and audit pack

Every chemical-industry HVAC project hands over a documentation pack that goes into the site EHS document control system and feeds into the next regulatory audit. The pack contents are:

• Hazardous-area classification drawings (AS/NZS 60079.10.1 and 10.2) signed by the responsible engineer.
• As-built single-line and isometric drawings of the duct network.
• Weld procedure specifications and welder qualification records for every TIG-welded joint.
• Mill certificates for 316L stainless sheet stock, traceable by heat number to each fabricated section.
• IECEx certificates for every fan, damper actuator, gas detector and electrical accessory inside a hazardous zone.
• Continuity-test records for every duct joint inside a hazardous zone, showing earth resistance below the Safety Case-defined limit (typically 1 Ω).
• Pressure-test records to the building integrity criterion.
• Cause-and-effect matrix for the gas-detection system showing normal-to-emergency mode transitions.
• Witness-test records for the emergency-mode air-change rate against a simulated gas-detector trip.
• Operating and maintenance manuals in English including spare-parts lists, lubrication schedules and inspection intervals.
• Cross-references to the site Safety Case showing where the ductwork is named as a layer of protection in bow-tie analyses.

SBKJ supplies the as-built, weld and material documentation for the SBKJ scope; the IECEx, hazardous-area classification and Safety Case integration documents are supplied by the principal designer or the site EHS team. The interface is defined at project award and walked through at the project pre-start meeting.

How SBKJ supports Australian chemical projects

SBKJ Group has supplied HVAC duct fabrication equipment to chemical, petrochemical, fertiliser, polymer and industrial-gas projects across 100+ countries since 1995. The Australian footprint runs through the SBKJ office in Box Hill North VIC for English-speaking after-sales, project engineering and spare-parts support. For chemical-industry projects we typically engage at one of three project phases:

• Design support. Pre-construction review of the duct material, joint, fan and damper scope against AS/NZS, NFPA and API references — usually as an unpaid courtesy to architects and consulting engineers who are sizing the fabrication-shop footprint.
• Shop equipment supply. Supply of the SBAL-V stainless auto duct line, SBTF-2020 spiral tubeformer, TIG seam welder and ancillary handling equipment to a buyer fabricating duct in their own shop. Lead time 16 to 24 weeks; on-site commissioning by SBKJ engineers.
• Toll fabrication via partners. For projects where the buyer prefers to procure duct directly rather than fabricate in-house, SBKJ partners with Australian fabrication shops that operate SBKJ equipment.

Cross-reference the why choose SBKJ summary, the SBKJ machine catalogue, the pricing and lead time guide and the 47-point HVAC duct machine buyer's checklist. For Australian standards reference material, see the AS 1668.2 Australian ventilation code reference.

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FAQ

What ductwork material is required for Australian specialty chemical plants?

Standard galvanised steel fails within months in concurrent acid, alkali, organic solvent and heat exposure. The default specification for primary chemical-process extract and supply ductwork in Australian explosives, agrochemical, polymer and industrial gas plants is 316L stainless with full TIG-welded longitudinal and circumferential seams. Hastelloy or Inconel is used where halogen acids or chlorine compounds are present at high temperature. Fibre-reinforced polypropylene or PVC-lined steel is acceptable for cold acid streams without solvent contamination. Galvanised steel is only suitable for office, control-room and warehouse HVAC physically separated from process areas.

What is a Major Hazard Facility and what does it mean for ductwork?

A Major Hazard Facility (MHF) is a site licensed under state Work Health and Safety regulations that handles Schedule 15 dangerous goods above threshold quantities. The Australian regime is the local equivalent of European SEVESO III and UK COMAH. MHF status drives a Safety Case obligation that flows down into HVAC design — emergency ventilation rates of 25 to 30 air changes per hour on toxic-gas or flammable-vapour detection, fail-safe damper logic, redundant fans on Category 1 critical extracts, AS/NZS 60079 zone-rated electrics for any fan or damper within a Zone 0, 1 or 2 envelope, and signed-off documentation that ductwork integrity is part of the bow-tie risk model.

Does ductwork inside a hazardous area need ATEX or IECEx certification?

The ductwork itself is passive sheet metal and is not certified as a product. What requires AS/NZS 60079 and IECEx certification is anything that can be an ignition source — fans, motors, dampers, sensors, lights, junction boxes and any duct-mounted electrical accessory. In Zone 1 and Zone 2 you also have to specify earthing continuity across every duct joint to dissipate static, an anti-static internal lining where powder is in suspension, and bonding straps across flexible connectors. SBKJ supplies hazardous-area ductwork with continuity-tested earthing and certified fan-and-damper packages from IECEx-listed brands.

What air change rate is required for chemical process areas?

AS 1668.2 specifies minimum mechanical ventilation rates by occupancy. For industrial chemical-process buildings the steady-state design is typically 6 to 12 air changes per hour on normal operation. The Safety Case for an MHF or for a building covered under AS 1940 flammable-liquid storage drives a higher emergency rate of 25 to 30 air changes per hour on toxic-gas or LEL detection, with damper logic that isolates non-affected zones to prevent cross-contamination. Industrial gas filling stations, ammonium nitrate magazines and agrochemical formulation rooms all sit in this elevated-rate envelope.

Why does galvanised ductwork fail in chemical plants?

Zinc coatings are sacrificial — they corrode preferentially to protect the underlying carbon steel. In a chemical plant the zinc is consumed within months by acid mist, alkali condensate or solvent vapour, and once it is gone the bare carbon steel underneath rusts at full speed. The failure mode is perforation followed by uncontrolled fugitive emission into the workshop, which breaches both AS 3780 corrosive-substance storage requirements and the duty-of-care provisions of state Work Health and Safety law. 316L stainless eliminates the failure mode by being intrinsically corrosion-resistant rather than relying on a sacrificial coating.

Which Australian chemical sites are Major Hazard Facilities?

The largest Australian MHFs by ammonium-nitrate and ammonia inventory include Orica Kooragang Island in Newcastle NSW and Orica Yarwun in Gladstone QLD, Yara Pilbara Nitrates and Yara Pilbara Fertilisers at Karratha WA, Dyno Nobel Moranbah in central QLD, Incitec Pivot Phosphate Hill in QLD, Incitec Pivot Geelong in VIC, Incitec Pivot Gibson Island in Brisbane, and CSBP Kwinana in WA. Agrochemical formulators such as Nufarm at Laverton VIC also operate under MHF or near-MHF threshold conditions. Each site has a published Safety Case that establishes the HVAC design envelope for its process buildings.