Trailer, Semi-Trailer and Truck Body Manufacturing HVAC Ductwork Guide — Australian Bodybuilders 2026

1. Why this guide is different from our automotive paint booth and bus depot articles

SBKJ has already published several long-form references adjacent to this one. The automotive paint booth HVAC duct guide covers the booth itself in detail — spray hall, flash-off, bake oven, prep deck and the recirculating air handling tree. The bus depot and coach terminal HVAC duct guide covers the maintenance, parking and refuelling envelopes that sit downstream of vehicle assembly. The EV and vehicle assembly plant HVAC duct guide covers the trim-and-final hall for OEM assembly. The auto dealership and service centre HVAC duct guide covers the customer-facing service workshop. The welding methods HVAC duct fabrication reference covers the welding technologies used in the SBKJ duct shop itself.

This guide picks up the entire upstream side of the heavy vehicle envelope — the bodybuilder plant that takes a bare chassis, a pile of structural steel and aluminium, a roll of sandwich panel stock, a pallet of trim components, and turns the lot into a finished trailer, semi-trailer, refrigerated trailer, tipper, tanker, vacuum truck, or heavy commercial truck body. The HVAC challenge is more diverse than the trim-and-final hall of an OEM assembly plant, because the bodybuilder carries every process step from raw chassis preparation through to drive-away inspection under one roof. A typical Australian bodybuilder will have a fabrication bay (cutting, bending, welding), a sub-frame assembly bay, a finishing bay (sandblast, prep, paint, bake), a trim and electrical bay, a hydraulic test bay, and a final inspection bay — each with its own ventilation class and each driving its own duct fabrication brief.

In the Australian market the framing standards are dense. AS 1668.2 sets the mechanical ventilation rates. AS 4254 Parts 1 and 2 set the duct construction. AS 1530.4 governs fire-rated penetrations. AS 4114 and NFPA 33 jointly govern the spray paint booth. AS 2809 applies where the plant fabricates road tank vehicles for bulk dangerous goods. AS/NZS 60079 governs hazardous-area classification in paint booths, solvent stores and refrigerant charge bays where A2L gases are used. AS 3902 sets the sleeper cabin specification for cabin manufacturers. VSB 6 and VSB 14 govern post-build modifications carried out at the bodybuilder. ADR 80/03 and ADR 80/04 set the heavy vehicle envelope the finished product has to meet. NHVR Performance-Based Standards covers oversize and high-productivity vehicle envelopes. ATA Technical Advisory Procedures fill in industry guidance gaps. This guide steps through every functional zone and explains what the duct has to do, what construction class it has to meet, and how the SBKJ machine line fabricates it.

2. The Australian bodybuilder footprint in 2026

Australia is one of the largest heavy commercial vehicle and trailer markets in the world on a per-capita basis, driven by long-distance freight transport across a continental landmass, mining haulage, agricultural cartage, and a relatively conservative truck retention cycle that supports a large rebuild and refit industry alongside new build. The market splits into three broad cohorts: heavy commercial truck assembly operators (the OEM and bodybuilder hybrid plants that produce the chassis and cabin); trailer manufacturers (the standalone plants that produce semi-trailers, drop-deck trailers, refrigerated trailers, tippers and tankers); and specialist bodybuilders (the smaller plants that adapt OEM chassis with custom bodies, refrigeration plant, vacuum tanks and the like).

2.1 Heavy commercial truck operators

The heavy commercial truck side of the Australian market is concentrated around a small number of high-volume assembly plants:

• PACCAR Australia at Bayswater Victoria. PACCAR's Bayswater plant assembles Kenworth and DAF heavy-duty trucks for the Australian and New Zealand markets and is the largest single-shed truck assembly operation in the southern hemisphere. The plant integrates a body-in-white bay, paint shop, trim and final hall, sleeper cab assembly cell and PDI bay under one roof on a precinct that has been continuously operating since the 1960s.
• Volvo Group Australia at Wacol Brisbane. Volvo Group Australia operates the Wacol assembly plant that builds Volvo, Mack and UD heavy-duty trucks for the Australian and New Zealand markets. The plant carries a full body-in-white bay, paint integration, trim and final hall and sleeper cab cell.
• Daimler Truck Australia Pacific at Mulgrave Victoria. Daimler Truck Australia Pacific assembles Fuso, Freightliner and Mercedes-Benz heavy trucks. The Mulgrave site combines chassis assembly with trim and final completion.
• Iveco Australia at Dandenong Victoria. Iveco's Dandenong plant has been a continuously operating Australian commercial vehicle assembly site since the 1950s and currently produces the Stralis heavy line, the Daily light commercial range and the ACCO vocational truck.
• Hino Motors Sales Australia at Caringbah NSW. Hino completes light and medium commercial trucks for the Australian market with bodybuilder integration on the same precinct.
• Isuzu Australia at Port Melbourne Victoria. Isuzu's Port Melbourne site handles imported commercial vehicle pre-delivery preparation and a long-standing bodybuilder partnership network across the Australian states.
• Scania Australia at Campbellfield Victoria and Eastern Creek NSW. Scania carries final-completion and customer-spec sleeper cab fit-out work at both Australian sites.
• Western Star Trucks at Penrith NSW. Western Star carries on-highway and vocational truck completion work for the Australian market.
• MAN Australia at Brisbane. MAN handles heavy commercial completion and aftermarket integration in Brisbane.
• Cummins Australia at Pinkenba Queensland and Scoresby Victoria. Cummins is an engine and powertrain supplier rather than a bodybuilder, but the engine factory is in scope as a major industrial HVAC client in the same cohort.

2.2 Trailer manufacturers

The trailer side of the Australian market is more fragmented and competitive:

• Krueger Transport Equipment at Dandenong Victoria, Wodonga Victoria and Toowoomba Queensland. Krueger is the largest Australian-owned trailer manufacturer and runs a high-volume operation producing curtainsiders, flat-decks, drop-decks, low-loaders and refrigerated trailers across three sites.
• Vawdrey Australia at Dandenong Victoria and Toowoomba Queensland. Vawdrey produces refrigerated trailers, tippers, semi-trailers and B-doubles across two sites and is a leading specialist in refrigerated transport equipment.
• Maxi-CUBE Trailers at Bayswater Victoria. Maxi-CUBE is the dedicated refrigerated trailer specialist and one of the largest reefer plants in the country, producing high-volume sandwich-panel insulated trailers for cold chain operators.
• Drake Trailers at Brisbane. Drake Trailers specialises in heavy haulage equipment including low loaders, multi-axle dollies and oversize trailers for the mining, infrastructure and defence sectors.
• Haulmark Trailers at Brisbane. Haulmark produces tippers, side tippers, walking floors and end tippers for the Australian aggregate and bulk haulage market.
• Lusty EMS at Sydney and Brisbane. Lusty EMS is a tipper and end-dump specialist with a long Australian production history.
• McKinney Trailers at Sydney NSW. McKinney is an established Sydney-based trailer manufacturer covering refrigerated and general-purpose lines.
• Tefco Australian Trailers at Melbourne. Tefco produces curtainsiders, drop-decks, semi-trailers and B-doubles for the Australian linehaul market.
• O'Phee Trailers at Toowoomba Queensland. O'Phee builds road train trailers and heavy haulage equipment specifically for the Queensland and Northern Territory linehaul market.
• Performance Engineering Group at Toowoomba. Performance Engineering is a multi-discipline manufacturer producing trailers, tippers and specialist heavy haulage.
• Hercules Trailers at Adelaide South Australia. Hercules covers general trailer manufacture for the South Australian and interstate freight market.
• Hamelex White at Perth Western Australia. Hamelex White is the Western Australian tipper and dolly specialist that supplies the WA mining haulage market.
• Howard Porter at Perth Western Australia. Howard Porter is a tipper and side tipper manufacturer with a long WA history.
• Trout River at Adelaide. Trout River builds moving-floor trailers and live-bottom trailers for the bulk and aggregate market.
• Robcam at Cobram Victoria. Robcam Engineering produces tippers, water tankers and specialist heavy bodies for the agricultural and contracting sectors.

2.3 Specialist bodybuilders, tanker and vacuum manufacturers

The specialist segment includes:

• Holmwood Highgate at Brisbane. Holmwood Highgate is the Australian specialist in chemical, petroleum and fuel tankers for the bulk dangerous goods transport market. The plant operates under AS 2809 throughout the fabrication and pressure test envelope.
• Tieman Tankers at Adelaide. Tieman is an Adelaide-based road tank vehicle manufacturer covering fuel, water and chemical transport.
• Brisbane Bulk Truck Tankers at Brisbane. Specialist bulk tanker manufacturer focused on cement, lime and dry powder transport.
• Manac Australia at Sydney. Manac builds vacuum trucks for the industrial cleaning, drainage and environmental services market.
• STG Global at Sydney. STG Global produces vacuum trucks, sewer cleaners and combination jet-vac equipment.
• JJ Richards Equipment at Brisbane. JJ Richards builds waste collection trucks and vacuum cleaning equipment for in-house fleet use and external sale.
• ProShark at Adelaide. ProShark is a multi-discipline bodybuilder covering vans, service bodies and light commercial conversion.
• BBC Body Builders at Sydney NSW. BBC handles heavy truck body completion for the Sydney commercial vehicle market.
• BCS Construction at Sydney. BCS specialises in heavy truck body construction for the construction and aggregate haulage market.
• Borgers Australia at Sydney NSW. Borgers manufactures specialty truck bodies for the Australian market.
• Mitsubishi Forklift at Hexham NSW. Mitsubishi Forklift's Hexham plant is a material handling vehicle operation in the same industrial HVAC cohort.
• Volgren Australia at Geelong Victoria and Brisbane Queensland. Although primarily a bus body builder, Volgren operates within the same manufacturing envelope as a heavy trailer plant.
• Custom Bus Group at Melbourne and Sydney. Custom Bus is a bus body builder with adjacent technology in the heavy trailer envelope.
• Bustech at Brisbane and Adelaide. Bustech builds bus and coach bodies, including the ZDi battery-electric platform.
• Mills-Tui at Brisbane. Mills-Tui builds bus bodies for the Australian commuter and tourist coach market.

The HVAC scope across these operators is dominated by five building types: large-span fabrication halls with heavy welding loads; spray paint booth and bake oven cells; sandblast booths; refrigerated trailer foam injection enclosures; and specialist test bays for hydraulics, pneumatics and refrigerant systems. The duct fabrication brief for SBKJ on these projects almost always reduces to the same machine line — SBAL-V galvanised duct line for the rectangular trunks, SBTF-1602 spiral tubeformer for the medium-bore branches, SBTF-2020 spiral tubeformer for the large-bore exhaust risers, SBSF-1525 stitchwelder in stainless 304L for the paint booth and foam injection discharge, and SBFB-1500 plate bender for structural plate.

3. The standards stack

Every HVAC ductwork specification in an Australian trailer or bodybuilder plant ultimately points back to one or more of the standards in the cluster below. None of them is optional, and every duct fitting that SBKJ ships into the Australian market is fabricated to be compatible with the dimensional, leakage and construction provisions of all of them. This is the longest standards stack of any industrial sector we cover, and reflects the fact that the bodybuilder plant carries every category of industrial process risk — mechanical, thermal, chemical, dust, vapour, explosion and fire — under one roof.

3.1 AS 1668.2 — mechanical ventilation in buildings

AS 1668.2 sets the design ventilation rates for occupied buildings in Australia. For a bodybuilder plant the relevant clauses are the light manufacturing classification (V_p of 4 L/s per person), the heavy manufacturing classification (V_p of 6 L/s per person), the welding classification (additional process exhaust supplement at 10 L/s per kilogram of consumable rate), the spray painting classification (cross-references AS 4114), and the dust classification (additional process exhaust at 1.0 m/s capture velocity over the work zone). A 150-occupant 6,000 m2 trailer plant typically lands on 9,000–14,000 L/s once V_p and V_b are accounted for, before process exhaust make-up. SBKJ duct sizing is anchored to that supply figure and a transport velocity of 7–10 m/s in the main supply trunks falling to 4–6 m/s at the diffuser tap-offs.

3.2 AS 4254 — ductwork for air-handling systems in buildings

AS 4254 is the Australian construction standard for sheet-metal ductwork. Part 1 covers flexible duct and Part 2 covers rigid sheet-metal duct. Together they prescribe gauge, joint type, hanger spacing, leakage class and dimensional tolerance for every duct fitting in the building. For trailer and bodybuilder work, almost all rectangular supply and return runs are AS 4254.2 medium-pressure construction (Class C leakage); welding fume collection trunks and paint booth riser duct are AS 4254.2 high-pressure construction (Class B leakage); and flexible drops to terminals are AS 4254.1 Class 1 with a maximum length of typically 1.5 m. The SBAL-V auto duct line that SBKJ supplies into the Australian market is configured by default to AS 4254 dimensional tolerances on length, width, squareness and flange flatness — the same Pittsburgh and TDF flange interface that the standard recognises as compliant. The detailed sheet metal envelope is covered in our AS 4254 Australian ductwork construction reference.

3.3 AS 1530.4 — fire-resistance test of building elements

AS 1530.4 governs the fire-resistance testing of building elements including duct penetrations through fire-rated walls. In a bodybuilder plant the fire rating between the paint booth, the bake oven, the solvent store and the general fabrication hall is typically 1-hour fire separation. Any duct penetration through a 1-hour fire-rated wall has to be either fitted with an AS 1668.1-listed fire damper or constructed as a fire-rated duct certified to AS 1530.4 / EN 1366. SBKJ ships AS 1668.1 fire damper interface flanges on every duct delivery into a paint booth zone as a standard inclusion. The broader fire and smoke envelope is covered in our fire and smoke damper integration reference.

3.4 AS 4114 and NFPA 33 — spray painting booths

AS 4114 is the Australian standard for spray painting booths and is the primary regulatory framing for the paint booth and bake oven in any bodybuilder plant. NFPA 33 is the US National Fire Protection Association standard for spray application using flammable or combustible materials and is referenced where the booth is supplied by a US-pattern equipment vendor or where the client specification calls for dual compliance. Both standards drive the same outcome: downdraft or semi-downdraft capture at 0.5 m/s through the work zone, exhaust through a dry-filter wall at 95% efficiency on overspray, fan motors and electrical equipment rated for the Class I Division 2 / Zone 1 hazardous area inside the booth, and a make-up air handler that conditions and filters the supply air. For trailer bodies (which can be 12–15 m long) the booth is typically semi-downdraft — supply ceiling over a partial length, exhaust wall over the full body length — rather than full downdraft, because the floor pit volume becomes uneconomic for a 15 m booth.

3.5 AS 2809 — road tank vehicles for bulk dangerous goods

AS 2809 sets the design and construction standard for road tank vehicles used to transport bulk dangerous goods including petroleum, chemicals and liquefied gases. It applies to the tanker manufacturers in section 2.3 above (Holmwood Highgate, Tieman, Brisbane Bulk Truck Tankers). From an HVAC point of view, the standard does not directly prescribe the ventilation envelope — that is on AS 1668.2 — but it drives the construction class of the pressure test bay (hydrostatic and pneumatic), the cleanout bay (where the tanker is purged between products), and the welding cells (where the longitudinal welds are made under specified procedure). All three are higher-class containment zones than a flat-deck trailer plant and the duct is fabricated accordingly.

3.6 AS/NZS 60079 — explosive atmospheres

AS/NZS 60079 is the Australian and New Zealand adoption of the IEC 60079 series for explosive atmospheres. In a bodybuilder plant the hazardous-area zones are the inside of the paint booth (Class I Zone 1 during spray operation, Zone 2 during purge), the solvent store (Zone 2), the refrigerant charge bay where A2L gases are used (Zone 2), the paint thinner mix room (Zone 1 or 2 depending on volume), and the LPG forklift charging cabinet if present. The HVAC duct that passes through or terminates in any of these zones is required to be either spark-resistant (aluminium or austenitic stainless) or to have a continuous earth bond across every joint, with the supply and exhaust fan motors rated to the corresponding Ex protection class.

3.7 AS 3902 — sleeper cab standards

AS 3902 sets the cabin sound and thermal envelope for sleeper cabs in heavy commercial trucks. It does not govern the manufacturing plant HVAC directly but it drives two pieces of plant HVAC scope: the cabin trim line, where the cabin acoustic and thermal insulation is installed and which requires controlled humidity to bond the adhesive layers correctly; and the cabin climatic test chamber, where the finished cabin is run through ADR 80/04 emission and AS 3902 thermal compliance testing. The trim line is on AS 1668.2 with comfort cooling and the climatic test chamber is on a dedicated air handler that can swing from -25 degrees Celsius to +50 degrees Celsius with controlled humidity.

3.8 VSB 6, VSB 14 and the ADR series — vehicle standards

Vehicle Standards Bulletin 6 (VSB 6) governs the modification of trailers in service, and VSB 14 governs the modification of heavy vehicles in service. They apply to the bodybuilders who carry out post-build conversion work — refrigerated trailer retrofits, tipper body installation, vacuum tank fitting, hydraulic crane mounting and the like. The Australian Design Rules series — particularly ADR 80/03 and ADR 80/04 for heavy vehicle emissions, and ADR 13 for trailer lighting — sets the envelope the finished vehicle has to meet. From an HVAC point of view, the bulletins and ADRs drive the test bay specification: where the bodybuilder performs end-of-line ADR 80/04 emissions verification, the dyno or static engine test cell needs full ICE exhaust capture; where the bodybuilder performs ADR 13 lighting compliance, the test bay is a photometric chamber with controlled blackout.

3.9 NHVR PBS — Performance-Based Standards

The National Heavy Vehicle Regulator (NHVR) administers the Performance-Based Standards (PBS) scheme for oversize and high-productivity heavy vehicles. PBS-certified trailers (PBS Level 2A, 2B, 3A, 3B and 4A) are designed to specific performance criteria for stability, braking, swept path and pavement loading. From an HVAC point of view, PBS does not directly govern plant ventilation, but it drives an additional category of end-of-line test bay scope at the higher-volume trailer manufacturers (Krueger, Vawdrey, Maxi-CUBE) where PBS certification testing is performed in-house. The test bay HVAC envelope is no different from the rest of the plant.

3.10 ASHRAE Applications Chapter 28 — industrial ventilation

ASHRAE Applications Chapter 28 is the international reference for industrial ventilation and is widely used in Australia as a parallel reference alongside AS 1668.2 and the Industrial Ventilation Manual published by ACGIH (American Conference of Governmental Industrial Hygienists). For each industrial process listed in this guide — welding, sandblasting, spray painting, foam injection, grinding, plasma cutting — ASHRAE Ch 28 publishes a recommended minimum capture velocity, transport velocity and filter type. SBKJ duct is sized to whichever of AS 1668.2 or ASHRAE Ch 28 is more demanding for the specific process, and we are willing to model both in the design submission.

3.11 Safe Work Australia WES — workplace exposure standards

Safe Work Australia publishes the workplace exposure standards (WES) that the HVAC system has to deliver. The standards that matter most in a bodybuilder plant are: welding fume 1 mg/m3 TWA, MEK 200 ppm TWA, toluene 50 ppm TWA, xylene 50 ppm TWA, MDI 0.005 ppm STEL (for PU foam injection), styrene 50 ppm TWA (for composite layup), respirable crystalline silica 0.05 mg/m3 TWA (for sandblast), iron oxide fume 5 mg/m3 TWA (for steel grinding and oxy-cutting). Each WES sets the design exhaust rate the duct system has to support, and each requires a margin against drift — SBKJ designs to 60% of the WES at design conditions so that filter loading, ductwork loss and unintended infiltration do not push the breathing-zone concentration over the standard.

4. Zoning the building

Before any duct can be sized, the building has to be zoned. A bodybuilder plant is not a single ventilation zone, and treating it as one is the most common mistake we see in early-stage tender drawings. The zoning logic that SBKJ uses on every Australian trailer or bodybuilder plant fit-out has fourteen functional groups, and every duct run in the building belongs to exactly one of them.

4.1 Chassis preparation and fabrication bay

This is the largest zone in any bodybuilder plant. Raw structural steel and aluminium stock arrives at the receiving dock, is moved through cutting (plasma, laser, oxy, shear), bending (press brake, plate roll), and pre-fabrication (drilling, machining, pre-assembly) into the welding cells. Process loads in this zone include welding fume (covered in section 5), cutting fume (plasma and laser, section 6), grinding dust (section 7), and ambient heat from machining processes. The HVAC envelope is heavy industrial supply-and-return with localised source capture at every fume-generating station.

4.2 Aluminium extrusion and sheet workshop

Many trailer manufacturers (Krueger, Vawdrey, Maxi-CUBE, Drake, Haulmark) carry aluminium fabrication alongside steel, particularly for sandwich panel cores, side rails and floor structures. Aluminium fabrication carries two HVAC risks that steel does not: magnesium content in aluminium alloys (typical 4–6% Mg in 5052 and 5083 grades commonly used for trailer panels) raises a fire risk in fine dust, and aluminium cutting fume reacts with moisture in steel duct to produce hydrogen gas in stagnant zones. The HVAC response is dedicated aluminium-only extract with spark-resistant duct construction — either aluminium duct fabricated on the SBAL-V configured for aluminium roll, or stainless 304 fabricated on the SBTF-1602. AS 3957 dust class C applies.

4.3 Welding cells (MIG, MAG, TIG, SAW)

Welding is the dominant process across the entire bodybuilder plant. Chassis frame welding uses MIG and MAG on heavy-section steel; sub-frame and bracket welding uses MIG and TIG; aluminium body welding uses pulsed MAG and TIG; main longitudinal beam welding (on trailer chassis) uses submerged arc. SAW is the heaviest single fume load in the plant on a per-metre basis. Source capture is the rule. Section 5 covers it in detail.

4.4 Plasma and laser cutting

Plasma cutting is the dominant cutting process for plate over 6 mm in most Australian bodybuilders, with laser cutting taking over for thinner plate and where dimensional precision matters. Both cutting processes carry a high local fume load with very fine particulate (sub-micron range, well into MERV 16 cartridge territory) and a thermal plume that drives natural buoyancy at the cutting head. Local extract is dedicated, ducted at high velocity (22–25 m/s) to cope with the fine particulate, and filtered to MERV 16 minimum. Section 6 covers it.

4.5 Robot welding cell

Higher-volume trailer manufacturers (Krueger Dandenong, Vawdrey Dandenong, Maxi-CUBE Bayswater) run robotic welding cells for the high-repetition longitudinal beam welds and chassis stitch welds. The cells are enclosed booths with positive door interlocks, integrated fume hoods on the robot frame, and dedicated extract to a central cartridge filter. The HVAC envelope is identical to manual welding but the duct routing is denser because each cell sees 8–15 weld zones in a confined volume.

4.6 Submerged Arc Welding (SAW) line

Submerged arc welding is used for the long longitudinal welds on the main trailer chassis beam and on the main truck frame rails. SAW produces less visible smoke than MIG or MAG because the flux blanket masks the arc, but the fume mass per metre is higher and is concentrated in iron oxide and silicate aerosol. The capture is via a slot hood within 200–400 mm of the leading edge of the flux, with the trailing flux removed by a vacuum recovery system that ties into the same exhaust riser. SAW extract is one of the heaviest single duct loads in the plant. Section 5.4 covers it.

4.7 Galvanising line (where present)

Some bodybuilders (particularly the heavier tipper and waste body manufacturers) operate an in-house galvanising line for the structural steel components. The line includes a pickling tank (sulphuric or hydrochloric acid), a flux tank, a zinc spelter bath at 450 degrees Celsius, and a quench. Each process carries a vapour or fume risk: acid mist from pickling, ammonium chloride fume from fluxing, zinc oxide fume from the spelter, and water vapour from the quench. The HVAC response is segregated local extract at each tank with stainless 316L duct (acid mist is corrosive to 304 over time) on the SBSF-1525 stitchwelder. Galvanising is a specialist sub-zone and we cover it in detail in our foundry HVAC guide with adaptations for trailer plant context.

4.8 Composite and GRP sandwich panel layup

Some trailer manufacturers (particularly the refrigerated trailer specialists) carry an in-house composite layup operation for sandwich panel skins, side wall panels and roof structures. Open-mould GRP layup releases styrene vapour at 30–200 ppm at the surface during the lay-down and cure phases; closed-mould resin transfer moulding releases substantially less. The HVAC response is dedicated styrene extract at 0.4 m/s capture velocity with a thermal oxidiser or activated carbon abatement upstream of roof discharge. Section 9 covers it.

4.9 Polyurethane foam injection (reefer only)

This is the defining process in a refrigerated trailer plant. The sandwich panel cavity between the inner and outer skins of a reefer trailer body is filled with two-component polyurethane foam — isocyanate component A reacted with polyol component B, mixed at high pressure and injected into the cavity, where it expands to 30× volume and cures to a rigid closed-cell foam. The mixing and injection process releases MDI vapour. MDI is the most stringently controlled substance in the plant with a Safe Work Australia STEL of 0.005 ppm — more than four orders of magnitude below MEK or toluene. Section 10 covers the HVAC envelope.

4.10 Sandblast booth

Sandblasting (and the newer abrasive blast media variants — garnet, glass bead, steel grit) is used to prepare the steel surface before painting. The booth captures the blast media and the dust through a downdraft extract, separates the blast media for recycling, and discharges the cleaned air through a cartridge filter. The dust load is dominated by the substrate (steel oxide and mill scale) plus the blast media (silica if natural sand, garnet if garnet, glass dust if glass bead). Section 11 covers it.

4.11 Wet wash and degreasing

Between blast and paint, the workpiece is washed and degreased to remove the residual oil and blast media. Wash chemistries range from alkaline (caustic soda based) for general work to acidic (phosphoric or chromic) for high-spec automotive-grade prep. Each carries vapour and aerosol loads that need local extract. The duct is fabricated in stainless 316L on the SBSF-1525 to handle the chemistry over a 20-year plant life.

4.12 Spray paint booth and bake oven

The spray paint booth is the single largest HVAC capital item in the plant. It carries a combined airflow of 30,000–80,000 L/s depending on body length and downdraft configuration, runs at a hazardous-area classification inside the booth, and has to integrate with the bake oven downstream. The booth ductwork is on the SBSF-1525 in stainless 304L where chlorinated solvents are present and on the SBAL-V in galvanised for the conditioned supply ducts. Section 12 covers it.

4.13 Cab trim assembly and final fit-out

The trim assembly bay carries solvent-adhesive vapour from headlining, dashboard and trim panel bonding, plus general comfort HVAC. Section 13 covers it.

4.14 Hydraulic test bay, refrigerant charge bay and PDI

End-of-line testing covers hydraulic ram and tipping mechanism testing (oil mist load), refrigerant charging for reefer trailers (R-744 CO2, R-452A, R-134a, plus emerging A2L gases), and pre-delivery inspection. Section 14 covers all three.

5. Welding fume capture in detail

Welding is the dominant fume load in any bodybuilder plant. The Safe Work Australia workplace exposure standard for welding fume has tightened in successive code revisions to 1 mg/m3 TWA, and is the design target for every duct sizing calculation in the welding zone. The plant compliance position is sensitive to a 60% margin against this standard at design conditions, which means SBKJ designs the welding extract to deliver 0.6 mg/m3 at the breathing zone under worst-case process load.

5.1 MIG and MAG welding

MIG (metal inert gas, argon shielded) and MAG (metal active gas, CO2 or argon-CO2 shielded) are the highest-volume welding processes in any Australian bodybuilder plant. Chassis frame welding, sub-frame welding, tipper body welding and bracket welding are all dominated by MIG and MAG with solid wire or flux-cored wire. The fume rate ranges from 0.5 to 2 g/min per gun depending on wire feed rate and shielding gas. On-torch fume extraction is the standard solution for new builds: a vacuum-extraction nozzle integrated into the torch head captures the fume at 50–100 L/s per gun within 50 mm of the arc. Where on-torch extraction is impractical (heavy-section work, restricted access, multi-pass weld), the backup is a slot hood within 200–400 mm of the arc at 0.5–1.0 m/s capture velocity, or an overhead canopy hood at 0.4 m/s capture velocity. SBKJ duct fabrication for the on-torch network is on the SBTF-1602 in 200–400 mm diameter, ducted at 18–22 m/s transport velocity.

5.2 TIG welding

TIG (tungsten inert gas) is used for aluminium body welding (5083 / 5052 alloys on trailer panels) and stainless welding (304 / 316 on tanker shells and food-grade refrigerated bodies). TIG produces less fume than MIG or MAG but the fume is finer (sub-micron) and contains more chromium and nickel on stainless work. Local extract is via on-torch fume extraction at 100–200 L/s per gun, or a slot hood at 0.5 m/s capture velocity within 300 mm of the arc. Stainless welding requires the duct to be in stainless construction because chromium and nickel fume condense on duct walls and produce a corrosion risk over time. We cover this in our welding methods HVAC duct fabrication reference.

5.3 Submerged Arc Welding (SAW)

SAW is used for the long longitudinal welds on the main trailer chassis beam (where one continuous weld can be 8–15 m long) and on the main truck frame rails. The arc is buried under a granular flux blanket that masks the visible arc and absorbs most of the radiant heat, but the fume mass per metre of weld is the highest of any welding process. Capture is by a slot hood within 200–400 mm of the leading edge of the flux blanket at 1.0 m/s capture velocity, with a parallel vacuum recovery system collecting the trailing un-melted flux for recycling. SAW extract is 300–500 L/s per slot hood with a duct transport velocity of 22 m/s to handle the iron oxide and silicate particulate. The riser is on SBTF-2020 in 600–800 mm diameter.

5.4 Robotic spot welding

Robotic spot welding is less common in trailer plants than in passenger-car assembly, but is used at higher-volume operators (Krueger, Vawdrey, Maxi-CUBE) for repetitive chassis welds. The cell is enclosed with positive interlocks and a single dedicated extract that runs continuously during the cell duty cycle. Cell extract sizing is 800–2,500 L/s per cell depending on weld density. Duct fabrication is the same as manual MIG — SBTF-1602 round branches and SBAL-V rectangular collection trunks. See our welding methods reference for cell sizing detail.

5.5 Filtration and discharge

The captured fume cannot simply be discharged. AS 1668.2 dispersion criteria require filtration to limit ground-level concentration at the building boundary. The default for weld fume is a cartridge filter bank rated MERV 14 or higher (MERV 16 increasingly common on new builds), with a face velocity of 0.4–0.5 m/s at the cartridge. The filter unit is sized 25–40% above peak demand to absorb cartridge loading between change-outs. Cartridges are pulse-jet cleaned on a programmed cycle, with the dislodged dust dropping into a sealed drum for disposal. Discharge is at roof level via the SBTF-2020 spiral riser, with stack height set 3 m above the eaves, discharge velocity 12–15 m/s, and stack-to-intake separation at least 8 m.

6. Plasma, laser and oxy cutting

Plasma cutting is the dominant cutting process for plate over 6 mm in most Australian bodybuilders, with laser taking over for thinner plate and high-precision work. Oxy cutting persists on heavier plate above 25 mm. Each process produces a different fume profile:

6.1 Plasma cutting

Plasma cuts through plate by ionising a gas stream to 20,000–30,000 K and using the resulting plasma jet to melt and blow out the kerf. Fume is dominated by iron and steel oxide aerosol in the sub-micron range, with a high thermal plume driving natural convection at the cutting head. Local extract is via a downdraft cutting table where the plate sits on a grid above a plenum, and the fume is drawn through the plate. Plenum airflow is sized to 1.5–2.5 m3/s per square metre of cutting bed. The duct from the plenum is at 22–25 m/s transport velocity to handle the fine particulate. Filtration is MERV 16 cartridge or higher. SBKJ duct for the plenum-to-filter run is on the SBTF-1602 in 500–800 mm diameter.

6.2 Laser cutting

Laser cutting (CO2 or fibre laser) operates on a similar capture principle — downdraft table with a plenum below the cutting zone — but the fume mass is lower and the particulate is even finer (well into sub-200 nm). The extract sizing is 1.0–1.5 m3/s per square metre of cutting bed. Filtration is MERV 17 cartridge or HEPA H13 where the laser is cutting galvanised stock (zinc fume is more toxic and the discharge concentration matters). Duct fabrication is the same as plasma. We cover the laser cutting extract in detail in our welding and cutting methods reference.

6.3 Oxy cutting

Oxy cutting is used for plate above 25 mm and is dominated by heavy iron oxide fume with a high thermal plume. Local extract is by overhead canopy hood at 0.5–1.0 m/s capture velocity, ducted at 18–22 m/s. Filtration is MERV 14 minimum. The duct is on the SBAL-V in galvanised because oxy fume is non-corrosive to galvanised over typical plant lives.

7. Grinding and finishing

Grinding follows almost every welding and cutting operation and produces a continuous dust load that has to be captured at source. The grinding wheel speed (typically 80 m/s for resin-bonded wheels) atomises the metal into a fine dust at the wheel periphery, with the heaviest dust falling within 1 m of the wheel and the finest fraction carrying 5–10 m on natural convection. Local extract is via a slot hood at 0.5 m/s capture velocity within 300 mm of the wheel, ducted at 18–22 m/s. Filtration is MERV 14 cartridge. Iron oxide fume WES is 5 mg/m3 TWA, which is more permissive than welding fume, but the dust load is continuous rather than intermittent and the time-weighted exposure is what matters. Duct fabrication on the SBTF-1602 in 200–400 mm diameter.

8. Robotic welding cells in detail

Higher-volume trailer manufacturers (Krueger Dandenong, Vawdrey Dandenong, Maxi-CUBE Bayswater) run robotic welding cells for repetitive longitudinal beam welds and chassis stitch welds. The cell is an enclosed booth with positive door interlocks, an integrated fume hood on the robot frame, and a dedicated extract that runs continuously during the cell duty cycle. The HVAC envelope is denser than manual welding because each cell sees 8–15 weld zones in a confined volume, but the principle is identical.

Cell extract sizing is 800–2,500 L/s per cell depending on weld density and dwell time. Duct construction is the same as manual MIG — SBTF-1602 round branches collected on an SBAL-V rectangular trunk. The cell control system ramps the extract from idle (200 L/s) to peak when the robot starts a weld and ramps back down on completion, with a 30-second tail to clear any retained fume. This VFD-controlled demand approach reduces fan energy by 40–60% across the duty cycle and is increasingly specified as a default at the higher-volume manufacturers.

9. Composite and GRP sandwich panel layup

Some trailer manufacturers (Maxi-CUBE Bayswater, Vawdrey Dandenong, particularly on bespoke refrigerated and food-grade work) carry an in-house composite layup operation for sandwich panel skins, side wall panels and roof structures. The two dominant processes are open-mould wet layup (where the resin is rolled onto a glass fibre reinforcement on an open mould) and closed-mould resin transfer moulding (where the resin is injected into a closed mould between two halves). Open-mould layup releases styrene vapour at 30–200 ppm at the surface during lay-down and cure; closed-mould RTM releases substantially less.

The HVAC response in the layup bay is twofold. First, dedicated styrene extract at 0.4 m/s capture velocity over the work zone, ducted to either a thermal oxidiser (for plants with sufficient throughput to justify the capital) or an activated carbon abatement (more common at the Australian volumes) before roof discharge. The Safe Work Australia styrene WES is 50 ppm TWA, and the design target is 30 ppm at the breathing zone to maintain a 60% margin against the WES. Duct fabrication is in stainless 304L on the SBSF-1525 stitchwelder where the styrene concentration at the duct wall exceeds 100 ppm, and in galvanised on the SBAL-V elsewhere.

Second, supply air conditioning — layup is sensitive to ambient temperature and humidity because the resin cure rate depends on both. Typical design conditions are 20–25 degrees Celsius and 40–60% RH, with tighter tolerances during high-spec work. The supply handler is a dedicated unit with bag-plus-pocket filtration and direct expansion or chilled-water cooling. The detailed composite envelope is covered in our composite manufacturing HVAC duct guide with adaptations for trailer plant context.

10. Polyurethane foam injection (refrigerated trailer plants)

This is the defining HVAC challenge in any refrigerated trailer plant and is the single most demanding zone in the bodybuilder envelope. The cavity between the inner and outer skins of a reefer trailer body — typically 80–100 mm wall thickness, 100–150 mm roof and 100–200 mm floor — is filled with two-component polyurethane foam. Component A is methylene diphenyl diisocyanate (MDI), component B is a polyol blend with catalysts and blowing agent (typically pentane or HFC). The two are metered at high pressure (100–200 bar) through a static mixer head and injected into the cavity, where they react exothermically and expand to 30× volume over 60–90 seconds, then cure to a rigid closed-cell foam over 6–12 hours.

10.1 MDI workplace exposure standard

The Safe Work Australia workplace exposure standard for MDI is 0.005 ppm short-term exposure limit (STEL). That is more than four orders of magnitude tighter than any other vapour in the bodybuilder plant. The compliance position is sensitive to a 60% margin against this STEL, which means SBKJ designs the foam injection extract to deliver 0.003 ppm at the breathing zone under worst-case process load. Any leak in the injection circuit, any open-mould injection without enclosed capture, or any cure step in an unventilated zone will push the breathing zone over the STEL.

10.2 Closed-mould injection

The preferred process is closed-mould injection — the inner and outer skins of the panel are mated in a press with the cavity sealed except for an injection port. The MDI vapour is contained within the closed cavity and the only exposure point is the injection port and any cavity vent. Closed-mould injection allows the capture to be localised at the port (0.5 m/s capture velocity within 100 mm of the injection point) and the cavity vent (0.5 m/s capture velocity within 200 mm). The extract per injection station is 100–200 L/s.

10.3 Open-mould injection

Some configurations — particularly for repair work or for non-standard cavities — require open-mould or partial-fill injection where the cavity is not fully closed. In these configurations the entire injection station is enclosed in a booth with positive door interlocks, sidedraft or downdraft extract at 0.5 m/s capture velocity across the entire booth section, and a backup extract that activates if the injection cycle exceeds 60 seconds. Booth extract is 1,500–3,000 L/s.

10.4 Cure zone ventilation

After injection the panel is moved to a cure zone where the foam fully sets over 6–12 hours. The cure is exothermic and releases residual MDI vapour, although at much lower rates than the injection itself. The cure zone is ventilated at 10–15 air changes per hour with extract at floor level (MDI vapour is denser than air) and supply at high level. The duct is fabricated in stainless 304L on the SBSF-1525.

10.5 Discharge and abatement

Captured MDI vapour cannot be discharged direct to atmosphere because the dispersion concentration at the building boundary would exceed the WES STEL. The standard abatement is an activated carbon scrubber upstream of the discharge stack, sized for a 5–10 year carbon replacement cycle. The discharge stack is at roof level with 3 m above-eaves stack height, 12–15 m/s discharge velocity, and a minimum 8 m separation from any building intake. The riser to the scrubber and the riser from the scrubber to the stack are both on the SBTF-2020 spiral tubeformer in stainless 304L.

10.6 Why the duct has to be stainless

The carbamate decomposition products of MDI are mildly acidic and over a 20-year plant life will pit galvanised duct from the inside. Stainless 304L is the standard specification, with 316L upgrade where the local environment is humid (coastal Queensland, Northern Territory). SBKJ fabricates the foam injection extract on the SBSF-1525 stitchwelder which produces a continuous longitudinal weld at 4–6 m/min on 1.2–1.5 mm 304L stock — the right combination of leak class, weld quality and throughput for the MDI extract scope. Maxi-CUBE at Bayswater Victoria and Vawdrey at Dandenong Victoria both run this duct architecture.

11. Sandblast booth

Sandblasting prepares the steel surface for painting. The booth captures the blast media (silica sand, garnet, glass bead, steel grit, aluminium oxide), the substrate dust (mill scale, rust, paint residue), and the carrier air. The booth design is a downdraft enclosure where the operator stands at the periphery and the airflow moves downwards through the work zone at 1.0 m/s minimum face velocity. The captured air-blast media mixture passes through a primary cyclone separator that recovers the heavy media for recycling, then through a cartridge dust collector with MERV 16 cartridges, then to a clean stack discharge.

11.1 Booth sizing

For a trailer chassis (12–15 m long, 2.5 m wide, 1.5 m deep prep envelope), the booth is typically 18 m long, 6 m wide and 4 m high internal — large enough to accommodate the chassis on a turntable and the operator with sufficient peripheral clearance. The downdraft airflow at 1.0 m/s face velocity over the 18 m × 6 m floor area is 108 m3/s — 388,800 m3/hr — which is substantially larger than the spray paint booth on the same plant. The duct from the booth floor to the cyclone is at 22–25 m/s transport velocity (silica is heavier than weld fume) and is on the SBTF-2020 in 1,200–1,800 mm diameter.

11.2 Silica WES

Respirable crystalline silica is the most heavily regulated dust in the Australian workplace. The Safe Work Australia WES is 0.05 mg/m3 TWA, halved from 0.1 mg/m3 in the 2020 code revision. The plant compliance position is sensitive to a 60% margin against this WES, which means SBKJ designs the sandblast extract to deliver 0.03 mg/m3 at the breathing zone outside the booth. Inside the booth the operator wears a positive-pressure supplied-air respirator regardless of the dust concentration, but the booth seal class still has to support the WES at the periphery.

11.3 Explosion isolation

NFPA 660 (Combustible Dust Standard, the consolidation of NFPA 652, 654, 655, 664 and 484) governs the explosion risk in any dust collector handling combustible dust. For metal substrate dust the explosion risk is real but modest; for aluminium or magnesium dust it is significant. The standard mitigation is an explosion isolation valve on the inlet duct between the booth and the collector, sized for the worst-case overpressure, plus an explosion vent on the collector roof. The duct between the isolation valve and the collector is rated for the overpressure (typically 1 bar burst pressure) which is well above the AS 4254.2 high-pressure class. The detailed dust collector envelope is covered in our cement plant HVAC duct guide with adaptations for sandblast booth context.

12. Spray paint booth and bake oven

The spray paint booth is the single largest HVAC capital item in any bodybuilder plant. For a trailer (12–15 m body length) the booth is typically semi-downdraft — supply ceiling over a partial length, exhaust wall over the full body length — rather than full downdraft, because a full downdraft floor pit on a 15 m booth becomes uneconomic. For a heavy truck (single cab plus prime mover, 6–8 m) the booth is full downdraft. The paint booth itself is covered in detail in our automotive paint booth HVAC duct guide; this section covers the bodybuilder-specific elements.

12.1 Booth sizing for trailer length

Semi-downdraft booths for trailers run at 50–80 m3/s total exhaust depending on body length. The supply ceiling delivers conditioned filtered air at 0.5 m/s downwards through the full body height. The exhaust wall captures the air via a dry-filter bank at 0.5–0.7 m/s face velocity, with 95% efficiency on overspray. The supply ducts are on the SBAL-V in galvanised at 8–10 m/s transport velocity; the exhaust ducts are on the SBSF-1525 stitchwelder in stainless 304L because the captured air carries solvent vapour that will corrode galvanised over time.

12.2 Hazardous area classification

Inside the booth during spray operations is a Class I Zone 1 hazardous area under AS/NZS 60079. The lighting, fans and electrical equipment inside the booth are rated to Ex protection class; the ductwork is bonded to earth with a continuous bonding strap; and the fan motor is mounted external to the booth on a non-hazardous side wall. The booth purge cycle reduces the zone class from Zone 1 to Zone 2 within 5 minutes of spray cessation, allowing access for maintenance.

12.3 Solvent exposure standards

The paint chemistry in a trailer plant is dominated by polyurethane two-pack systems for the exterior finish, alkyd or acrylic primer underneath, and water-based or solvent-based intermediate coats. The solvents present at any one time include MEK (methyl ethyl ketone, WES 200 ppm TWA), toluene (WES 50 ppm TWA), xylene (WES 50 ppm TWA), MIBK (methyl isobutyl ketone, WES 50 ppm TWA), and the isocyanate hardener (an isomer of MDI or HDI, both with STELs at 0.005 ppm). The booth design has to deliver an operator breathing zone below 60% of each WES under the worst-case spray schedule.

12.4 Bake oven integration

The bake oven downstream of the spray booth heats the painted body to 60–80 degrees Celsius for 30–60 minutes to cure the polyurethane finish. The oven exhaust carries residual solvent vapour and isocyanate fume and is held under negative pressure relative to the spray booth. The oven discharge ducts to the same roof stack as the spray booth, with a thermal oxidiser or activated carbon abatement at the stack base where the local environmental authority requires VOC abatement.

12.5 Stainless paint booth ductwork

For paint booths handling chlorinated solvent paints (less common in 2026 but still used in specialist coatings), the exhaust ductwork has to be stainless 304L or 316L because the chlorinated decomposition products will pit galvanised over 5–10 years. SBKJ fabricates the booth exhaust on the SBSF-1525 stitchwelder which produces a continuous longitudinal weld in stainless at 4–6 m/min on 1.2–1.5 mm 304L stock. Where the booth handles only modern polyurethane chemistries, galvanised on the SBAL-V is acceptable but we still recommend stainless for the 10–15 year plant life advantage.

13. Cab trim assembly and electrical fit-out

The trim assembly bay is where the cabin interior is installed: headlining, dashboard, seats, side panels, carpet, glass, electrical harness, and instrumentation. The HVAC envelope is comfort cooling at 22–24 degrees Celsius and 40–60% RH, with a localised extract at any glue-down station. The solvent adhesives used in trim bonding release MEK, toluene and xylene at the lay-down point and require local extract at 0.4 m/s capture velocity within 400 mm of the bead. The duct is on the SBAL-V in galvanised with a roof discharge through a small carbon scrubber.

The electrical fit-out is a low-fume operation with no specific HVAC load beyond comfort cooling and the AS 1668.2 occupant ventilation rate. The exception is where the bodybuilder carries an in-house wiring harness manufacturing operation — in those plants the soldering line carries lead-free solder fume (rosin-based flux is the dominant exposure) which is captured at the bench by a small dedicated extract at 0.4 m/s capture velocity within 300 mm of the soldering iron. Bench extract per station is 80–120 L/s.

14. Hydraulic test bay, refrigerant charge bay and PDI

End-of-line testing is a small but important HVAC scope. Each test bay has its own ventilation requirement driven by the test process.

14.1 Hydraulic test bay

The hydraulic test bay is where the tipper ram, the trailer landing leg, the refrigerated trailer side door mechanism and any other hydraulic system are pressure-tested before delivery. The test carries an oil mist load from atomised hydraulic oil at the high-pressure connections (5–30 MPa typical) and a small thermal load from the heated oil. The HVAC response is local extract at the rig at 0.4 m/s capture velocity, ducted through a coalescing filter to recover the oil aerosol, with the recovered oil returning to a reservoir. The bay extract is 800–1,500 L/s. Duct fabrication in galvanised on the SBAL-V with a sloped low point to the coalescer drain.

14.2 Refrigerant charge bay (reefer only)

For refrigerated trailer manufacturers (Maxi-CUBE, Vawdrey, Krueger Refrigerated), the refrigerant charge bay is where the trailer's refrigeration unit (Thermo King or Carrier, typically) is charged with refrigerant before delivery. The dominant refrigerants in 2026 are R-744 (CO2, A1 non-flammable), R-452A (HFO blend, A1), R-134a (HFC, A1 but high GWP), and increasingly R-454C and R-1234yf (A2L mildly flammable). The HVAC response depends on the refrigerant class:

• R-744 (CO2). Ventilation at 6 ACH minimum with a low-level CO2 sensor (CO2 is denser than air and pools at floor level) tied to a ramped extract that increases to 20 ACH on alarm. Duct is on the SBAL-V in galvanised. No hazardous-area classification.
• R-452A, R-134a, R-507. Ventilation at 4 ACH minimum with a refrigerant leak detector tied to a 20 ACH emergency purge. Duct is on the SBAL-V in galvanised. No hazardous-area classification.
• R-454C, R-1234yf, R-32 (A2L mildly flammable). Ventilation at 4 ACH minimum with a refrigerant leak detector and an explosion-rated 20 ACH emergency purge. The bay is classified as Zone 2 under AS/NZS 60079 and the duct is in spark-resistant aluminium fabricated on the SBAL-V configured for aluminium, with continuous earth bonding across every joint and Ex-rated fan motors.

14.3 Tanker pressure test bay

Tanker manufacturers (Holmwood Highgate, Tieman, Brisbane Bulk Truck Tankers) operate a pressure test bay where the tanker shell is hydrostatically pressure-tested before delivery. AS 2809 applies. The bay is a wet environment with a 4 ACH supply rate and a low-level drain to capture leak water. For pneumatic test bays (where present), the bay is enclosed with an explosion-relief panel sized for the worst-case overpressure and a 10 ACH emergency purge. The duct is fabricated in stainless 304L on the SBSF-1525 to handle the wet environment over the plant life.

14.4 PDI bay

Pre-delivery inspection is the last station before the finished trailer or truck is handed over to the customer. The HVAC envelope is comfort cooling (22–26 degrees Celsius), AS 1668.2 occupant ventilation, and a dedicated wash-bay extract on any wet wash section. The wash-bay extract is in galvanised with sealed slip joints and a sloped low point to a condensate drain. The PDI bay is otherwise unremarkable from an HVAC point of view.

15. Driver cab climatic test cell (sleeper cab manufacturers)

PACCAR Bayswater, Volvo Wacol, Daimler Mulgrave, Iveco Dandenong and Western Star Penrith all produce sleeper cab variants for the long-distance Australian linehaul market. The sleeper cab carries an integrated cabin HVAC system (heating, ventilation, air conditioning, sleeper bed climate) that has to meet AS 3902 (cabin sound and thermal envelope) and pass ADR 80/04 emissions compliance for the integrated parking heater. Validation of the cab HVAC system requires a climatic test chamber that can swing temperature from -25 degrees Celsius to +50 degrees Celsius with controlled humidity, simulating Australian winter and summer extremes.

The climatic test chamber HVAC envelope is a dedicated air handler with a glycol-cooled coil, an electric or gas-fired heating coil, and a steam or ultrasonic humidifier. The supply duct is fabricated in insulated stainless 304L on the SBSF-1525 (the chamber goes through dew-point conditions during the cold-soak phase and galvanised would corrode). The return duct is the same construction. The chamber walls themselves are insulated sandwich panels typically supplied by the chamber vendor; the HVAC duct is on SBKJ's scope.

16. Acoustic and energy framing

HVAC noise in a bodybuilder plant has two failure modes. The first is interfering with the workplace audibility of the line stop alarms, which is a safety-critical concern. The second is rising above the workplace exposure standard for noise, which under Safe Work Australia model regulations is 85 dB(A) over an 8-hour shift. The HVAC contribution to these failure modes is dominated by duct-borne fan noise from the welding extract and the sandblast booth.

The standard acoustic class for an Australian bodybuilder hall is NC-55 (approximately 60 dB(A)) in the fabrication area, NC-50 in the trim and assembly area, NC-40 in the offices and break rooms, and NC-60 in the sandblast booth periphery where protective hearing is mandatory. Achieving NC-55 in a hall with high-airflow welding extract requires either lined duct silencers on the extract trunks or oversized duct with low velocity. SBKJ defaults to oversized duct — a 30% over-size on the trunk diameter relative to the strict aerodynamic minimum — because it eliminates the silencer maintenance burden over the 15-year plant life. The detailed acoustic treatment is covered in our acoustic HVAC duct lining and attenuator guide.

On the energy side, more Australian bodybuilder clients are targeting a NABERS for Industrial energy benchmark, particularly where the plant is built or refurbished against a corporate sustainability commitment. NABERS for Industrial rewards low specific fan power, low duct leakage, demand control on process exhaust, and recovery of waste heat from process exhaust streams. The duct fabrication implications are tighter leakage class than the AS 4254 minimum (Class B or C rather than the default Class D), VFD-driven fans on every process exhaust, and a heat-recovery loop on the welding extract where the waste-heat enthalpy supports it. SBKJ duct is fabricated to Class B leakage as the default on every project where the client specification calls for a NABERS rating.

17. The SBKJ machine line for an Australian bodybuilder plant

Across all of the zones above, the SBKJ machine configuration that fabricates the duct is consistent. There are five machines that do almost all of the work.

17.1 SBAL-V — galvanised auto duct line for rectangular trunks

The SBAL-V auto duct production line is the workhorse for rectangular supply, return and exhaust trunks across the building. It coil-feeds 0.5–1.5 mm galvanised steel at line speeds up to 16 m/min, cuts to length, notches, beads, and folds into a TDF-flange box section in a single pass on an 87 kW power envelope. Maximum duct width is 1,500 mm. Output is typically 8–12 m of finished rectangular duct per minute on production-cycle settings. The SBAL-V is configured by default for AS 4254.2 dimensional tolerances and ships with a Siemens or Mitsubishi PLC depending on the buyer's preference. For the majority of supply and return duct in a typical Australian bodybuilder plant — the chassis bay supply, the assembly hall return, the welding extract collection trunks, the amenities supply — the SBAL-V is the right machine. The full machine specification is at our SBAL-V product page.

17.2 SBAL-III — mid-range galvanised auto duct line

The SBAL-III is the mid-range predecessor of the SBAL-V, running at 14 m/min on a 15.7 kW power envelope. It is the right machine for smaller bodybuilder plants where the duct fabrication volume does not warrant the full SBAL-V capacity, or as a second line in larger plants where the SBAL-V is dedicated to high-volume production and the SBAL-III handles smaller-batch and specials work. We compare the two lines in auto duct line ROI cost analysis.

17.3 SBAL-II — entry galvanised auto duct line

The SBAL-II runs at 18 m/min on a 5.5 kW power envelope and is the entry-level auto duct line in the SBKJ range. It is the right machine for specialist bodybuilders carrying a smaller HVAC duct fabrication scope — typically the duct shop attached to a vacuum truck manufacturer or a smaller tipper plant — where the duct volume does not warrant a higher-capacity line.

17.4 SBTF-1602 — medium-bore spiral tubeformer

The SBTF-1602 spiral tubeformer fabricates round duct from 200 mm to 1,600 mm diameter in galvanised, aluminium or stainless construction. For the medium-bore branches in a typical Australian bodybuilder plant — the welding cell collection branches, the sandblast booth supply, the foam injection zone extract on reefer plants, the refrigerant charge bay extract, the cab trim extract — the SBTF-1602 is the natural fit. Output is typically 12–18 m per minute on a 600 mm diameter coil, falling to 6–8 m per minute at 1,200 mm diameter. Machine variants include the SBTF-1500C for medium-volume work and the SBTF-2020 for large-bore work.

17.5 SBTF-2020 — large-bore spiral tubeformer

The SBTF-2020 spiral tubeformer fabricates round duct from 1,000 mm to 2,000 mm diameter and is the machine that produces the main exhaust risers — paint booth exhaust, sandblast booth exhaust, SAW riser, plasma cutting plenum riser, smoke management riser. The SBTF-2020 is also the right machine for the supply main on a large-span fabrication hall where the design airflow exceeds 25,000 L/s on a single trunk. Output is typically 4–8 m per minute on a 1,500 mm diameter coil, falling to 2–4 m per minute at 2,000 mm diameter. The machine ships in a 12 m × 4 m footprint with a 6 m run-out, and is the largest single piece of HVAC machinery on most bodybuilder plant fit-out projects.

17.6 SBSF-1525 — longitudinal stitchwelder for stainless ductwork

The SBSF-1525 stitchwelder produces a continuous longitudinal weld on rolled stainless 304L or 316L plate up to 1,525 mm wide, running at 4–6 m/min on 1.2–1.5 mm stock with a 2.5 kW power envelope. The SBSF-1525 is the machine that fabricates the stainless ductwork for the paint booth exhaust, the foam injection extract, the chemical wash station extract, the tanker test bay extract, and the climatic test chamber. Where the trailer or bodybuilder plant carries any of these processes, the SBSF-1525 is essential. SBKJ ships the SBSF-1525 alongside the SBAL-V as the standard package for refrigerated trailer manufacturers and tanker manufacturers.

17.7 SBFB-1500 — plate bending machine for booth structural plate

The SBFB-1500 is a plate bending machine running at 1.20 m/min on a 7.5 kW power envelope, bending plate up to 1,500 mm wide. The machine is used for the structural plate components of the paint booth, sandblast booth and large fabrication enclosures — corner panels, end caps, transition pieces and reducers that cannot be formed on the SBAL-V or the spiral tubeformer. The SBFB-1500 is supplied as a standard kit alongside the SBAL-V on every bodybuilder plant fit-out where the booth fabrication is on SBKJ's scope.

17.8 Ancillary machines — SBTF-1500C, SBEM-1250, SBHF, SBPC1500, SBLR-600

The remaining SBKJ machines round out the bodybuilder fit-out scope. The SBTF-1500C is a compact spiral tubeformer for medium-bore round duct. The SBEM-1250 is an elbow machine that produces high-volume preformed elbows for the bodybuilder duct shop. The SBHF is the hard-flange machine for ductwork joining. The SBPC1500 is the Pittsburgh seamer for rectangular duct corner seams. The SBLR-600 (and the higher-output SBLR-600A) is the longitudinal seam roller for round duct, running at 7.6 m/min, used for the manual round duct fabrication where the spiral tubeformer is not the right tool. These ancillary machines collectively round out the duct shop and are typically supplied alongside the primary SBAL-V on the same kit. For a comparison of the full machine range, see our machines catalogue.

18. Procurement timeline for a bodybuilder plant fit-out

A typical Australian bodybuilder plant fit-out has an 18–24 month design and construction window, of which the HVAC ductwork procurement and installation occupies 6–10 months on the critical path. The phasing breaks down as follows.

• Months 1–3 — concept design. Plant zoning is set, the standards stack is agreed (AS 1668.2, AS 4254, AS 1530.4, AS 4114, AS 2809 if tankers, AS/NZS 60079, AS 3902 if sleeper cabs, VSB 6 and VSB 14, ADR 80/03 and 80/04), and the design airflows are calculated to a 70% confidence level. SBKJ is typically engaged at this stage for the machine line specification.
• Months 4–6 — detailed design. Duct routing is finalised on a 3D BIM model, fitting take-offs are produced, and the duct fabrication scope is tendered. SBKJ machine line is ordered with 12–16 week delivery to site.
• Months 7–9 — fabrication start. The first SBAL-V rectangular trunks are fabricated and delivered to site for first-fix installation. Spiral runs follow on the SBTF-1602 and SBTF-2020 as the trunk routing is verified on site. Stainless runs on the SBSF-1525 follow.
• Months 10–14 — installation. Trunk installation, branch installation, terminal installation and air-balancing run sequentially. The welding extract and paint booth are typically the last systems to be commissioned because they depend on the welding cells and the paint booth being installed and their final-position confirmed.
• Months 15–18 — commissioning and balancing. Final balancing to design airflow, leakage testing to AS 4254 Class B or C as applicable, and acceptance testing against the project specification.
• Months 19–24 — production ramp. The plant moves from commissioning into pilot production and then full production. The HVAC system is monitored against design and any reactive adjustments are made.

The single biggest schedule risk in this window is the paint booth and the sandblast booth — both have lead times of 16–24 weeks from order, and any change in the booth specification late in the design phase ripples through the whole exhaust scope. SBKJ engineering can compress the duct fabrication side of that ripple to 6–8 weeks where the order is placed on a stocked-coil specification, but the booth equipment lead time is on the booth vendor's scope and outside our control.

19. The supplier-park dimension

A typical Australian bodybuilder plant sits inside a supplier-park environment — a cluster of feeder buildings on the same precinct that supply structural sections, axle and suspension components, hydraulic assemblies, refrigeration units (for reefer plants), and tanker fittings (for tanker plants). The HVAC duct work in the supplier-park feeder buildings is in scope on most projects because the plant operator wants a single duct fabrication contract across the precinct.

The major Australian bodybuilder precincts are: Dandenong Victoria (Krueger, Vawdrey, Iveco, surrounding component suppliers); Bayswater Victoria (PACCAR, Maxi-CUBE, surrounding component suppliers); Wacol Brisbane (Volvo Group Australia, surrounding component suppliers); Mulgrave Victoria (Daimler Truck Australia Pacific, surrounding component suppliers); Toowoomba Queensland (Vawdrey, Krueger, O'Phee, Performance Engineering, surrounding component suppliers); and Adelaide South Australia (Hercules, Tieman, Trout River, ProShark, surrounding component suppliers). In each cluster the duct fabrication work flows across multiple buildings, and the SBKJ machine line is configured to handle that volume — typically with a single SBAL-V producing 30–50% of the precinct's rectangular duct annual demand and one SBTF-1602 plus one SBTF-2020 covering the round duct.

20. SBKJ's footprint in the Australian bodybuilder market

SBKJ Group has been supplying HVAC duct fabrication machinery into Australian trailer, bus body, refrigerated trailer, heavy truck and specialist bodybuilder plants for more than a decade. Our Box Hill North VIC office handles project engineering and after-sales for the Australian, New Zealand and Pacific markets, with engineers who have commissioned SBAL-V, SBAL-III, SBTF-1602, SBTF-2020 and SBSF-1525 machines into duct shops at trailer manufacturers, refrigerated trailer specialists, heavy commercial vehicle operators and specialist bodybuilders across the Dandenong, Bayswater, Wacol, Mulgrave, Toowoomba, Sydney, Adelaide and Perth precincts. The English-speaking after-sales line and the Box Hill North parts inventory are the differentiators that matter most on a 10–15 year machine life — when a roller bearing fails on a Friday afternoon at Toowoomba, the spare part is on a courier truck out of Melbourne by Monday morning.

For an Australian bodybuilder plant fit-out brief, the typical SBKJ machine package is: one SBAL-V auto duct line in galvanised for the rectangular trunk fabrication; one SBTF-1602 spiral tubeformer for the medium-bore branches; one SBTF-2020 spiral tubeformer for the large-bore exhaust risers (paint booth, sandblast booth, SAW); one SBSF-1525 stitchwelder in stainless 304L for the paint booth exhaust, foam injection extract (reefer plants only) and tanker test bay (tanker plants only); one SBFB-1500 plate bending machine for booth structural plate; and ancillary machines (SBEM-1250 elbow, SBPC1500 Pittsburgh, SBLR-600A round seamer) as required by the duct shop layout. The package ships in three to five 40-foot HC containers, installs in 10–14 days on site, and commissions to first article within 6–8 weeks of arrival. We size every quotation against the buyer's specific coil specification, the buyer's specific bodybuilder zoning, and the buyer's specific compliance package — AS 4254 minimum, with AS 1668.2 ventilation provisioning, AS 4114 paint booth integration, AS 2809 tanker provision where the scope warrants it, and AS/NZS 60079 hazardous-area construction where the paint booth or refrigerant charge bay warrants it.

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21. FAQ

Which Australian standards govern HVAC ductwork in trailer and truck bodybuilder plants?

A trailer or truck bodybuilder plant operates under at least nine simultaneous regulatory framings. AS 1668.2 sets the mechanical ventilation rates. AS 4254 Parts 1 and 2 set the construction class for the duct. AS 1530.4 governs fire-rated penetrations. AS 4114 and NFPA 33 govern the spray paint booth. AS 2809 applies to road tank vehicle work. AS/NZS 60079 governs hazardous areas. ADR 80/04 and ADR 80/03 set the heavy vehicle envelope. VSB 6 and VSB 14 govern post-build modifications. SBKJ duct fabricated to AS 4254 dimensional tolerances on the SBAL-V auto duct line satisfies the construction provisions of all of the above for the HVAC portion of the plant.

What is special about HVAC for a refrigerated trailer (reefer) manufacturer compared to a flat-deck trailer plant?

A reefer plant carries polyurethane foam injection into the sandwich panel cavity. The two-component PU foam releases MDI vapour, which has a Safe Work Australia STEL of 0.005 ppm — over four orders of magnitude tighter than any other vapour in the plant. The HVAC response is dedicated source capture at every injection station with a downdraft or sidedraft hood at 0.5 m/s capture velocity, a separate exhaust riser through a carbon scrubber to roof discharge, and a separate make-up air handler for the injection zone. The duct is in stainless 304L on the SBSF-1525 stitchwelder. Maxi-CUBE at Bayswater Victoria and Vawdrey at Dandenong are the largest Australian reefer plants and both run this duct architecture.

How is welding fume controlled in a trailer or truck bodybuilder plant?

Welding is the dominant fume load. MIG and MAG welding on chassis and sub-frame stations carry the heaviest load, with SAW on the main longitudinal beams carrying the highest fume mass per metre of weld. The Safe Work Australia WES is 1 mg/m3 over an 8-hour TWA. Source capture is the default: on-torch extraction at 50–100 L/s per gun for MIG and MAG, slot hoods within 200–400 mm of the arc for SAW and TIG, and overhead canopy hoods for spillover on heavy chassis stations. The captured fume is ducted at 18–22 m/s to a cartridge filter bank with MERV 14 or higher filtration, and discharged at roof level to AS 1668.2 dispersion criteria.

What is the right SBKJ machine configuration for an Australian trailer or bodybuilder plant fit-out?

SBKJ specifies the SBAL-V auto duct line in galvanised steel for the rectangular trunks; the SBTF-1602 spiral tubeformer for medium-bore branches; the SBTF-2020 spiral tubeformer for large-bore exhaust risers serving the paint booth, sandblast booth and SAW capture; the SBSF-1525 stitchwelder in stainless 304L for paint booth solvent vapour and MDI-laden reefer foam injection extract; and the SBFB-1500 plate bending machine for booth structural plate. Where the plant carries a hazardous area at the paint booth or solvent store, the spiral runs in those zones are configured for spark-resistant construction with grounded bonding straps across every joint.

How does the PU foam injection extract for a refrigerated trailer plant differ from a paint booth extract?

Both are solvent-vapour extract systems but the contaminant and the regulatory framing are different. A paint booth carries solvent vapours with WES in the 50–200 ppm range (toluene 50 ppm, xylene 50 ppm, MEK 200 ppm) under AS 4114 and NFPA 33 with a 0.5 m/s downdraft capture and a single-pass air handler. A PU foam injection extract carries MDI vapour with a WES STEL of 0.005 ppm under AS 1668.2 and the Safe Work Australia Code of Practice for isocyanates. The injection station is treated as a higher-class containment with closed-mould injection wherever the design allows, an enclosing booth around any open-mould injection, sidedraft or downdraft capture at 0.5 m/s, and a dedicated stainless 304L extract to a carbon scrubber and stack discharge. The two systems are never combined on the same exhaust riser.

Are heavy commercial vehicle assembly plants in scope for this guide?

Yes. PACCAR Bayswater (Kenworth, DAF), Volvo Group Australia Wacol (Volvo, Mack, UD), Daimler Truck Mulgrave (Fuso, Freightliner, Mercedes-Benz), Iveco Dandenong (Stralis, Daily, ACCO), Hino Caringbah, Isuzu Port Melbourne, Scania Campbellfield and Eastern Creek, Western Star Penrith and MAN Brisbane all operate final-assembly halls or bodybuilder add-on plants that fit the framing in this guide. The HVAC scope is the same architecture: chassis bay supply and return, welding cell source capture, sandblast booth extract, paint booth integration and amenities.

How is the spray paint booth on a 15 m trailer different from a passenger-car paint booth?

For trailer bodies (12–15 m long), full downdraft booths become uneconomic because the floor pit volume drives capital and maintenance cost out of proportion to the benefit. The standard configuration is semi-downdraft — supply ceiling over a partial body length with exhaust through a dry-filter wall over the full body length. Combined airflow is 50–80 m3/s. The booth interior is a Class I Zone 1 hazardous area under AS/NZS 60079 during spray operations. The exhaust ductwork is in stainless 304L on the SBSF-1525 stitchwelder where chlorinated solvents are used, and in galvanised on the SBAL-V where modern polyurethane chemistries only are present.

What ventilation is required in a refrigerant charge bay for new reefer trailers?

For R-744 (CO2, A1), 6 ACH minimum with a low-level CO2 sensor and ramped extract. For R-452A, R-134a and R-507 (A1 HFC), 4 ACH minimum with a refrigerant leak detector and 20 ACH emergency purge. For R-454C, R-1234yf and R-32 (A2L mildly flammable), 4 ACH minimum with leak detector and explosion-rated 20 ACH emergency purge. The bay is classified Zone 2 under AS/NZS 60079 for A2L gases and the duct is spark-resistant aluminium with continuous earth bonding and Ex-rated fan motors.