Mining Ventilation HVAC Duct Guide — Underground, Surface, Refuge Bay, AS/NZS 1668.4 Compliance

Why mining ventilation is unique among HVAC applications

HVAC for a commercial office tower has one job — keep occupants comfortable and meet AS/NZS 1668.2 outdoor air rates. HVAC for a hospital or pharmaceutical clean space adds particulate counts, pressure cascades and validation. Mining ventilation operates in a fundamentally different regime. The duct circuit is not delivering 20 air changes per hour to a 3-metre ceiling void. It is delivering tens of thousands of litres per second across kilometres of underground heading at velocities that would tear the lining off a hospital ceiling, against a static head measured in kilopascals, while simultaneously diluting toxic exhaust, removing geothermal heat and pressurising refuge bays against blast events. Every one of those obligations is a regulator-enforced safety function, not an occupant-comfort target.

The five non-negotiable functions a mining ventilation HVAC system must deliver, in priority order, are: (1) remove heat from working faces so wet-bulb temperatures stay within human tolerance; (2) dilute and remove diesel particulate matter, nitrogen dioxide, carbon monoxide and aldehydes from diesel-powered equipment; (3) suppress and remove airborne dust from drilling, blasting and material handling; (4) clear blast fumes from headings within shift-start time; and (5) maintain positive pressure isolation of refuge bays so workers have a survivable retreat point during a fire, explosion or inrush event. In coal mines you add a sixth — dilute methane below the lower explosive limit at every cross-section of every working district, continuously, every minute of every shift.

Each of those functions has its own duct architecture, its own material specification, its own sealing standard and its own regulator-imposed test regime. The duct circuit you specify for a Pilbara iron ore decline portal carrying surface ambient air to a refuge chamber 800 metres below ground is not the same duct you specify for the smelter offgas line at Olympic Dam. They have one thing in common — both are HVAC ductwork, both can be fabricated on the same family of coil-fed forming machines, both must be specified by an engineer who understands the difference. This guide is for that engineer.

The Australian mining HVAC landscape

Australia has the largest and most varied portfolio of working mines in the OECD, and that diversity drives the duct specification. The Pilbara iron-ore province in Western Australia is dominated by surface operations — Rio Tinto, BHP and Fortescue Metals Group run open-pit mines where the HVAC scope is concentrated on processing plants, ore beneficiation circuits, control rooms and crew accommodation. Underground HVAC is limited to deep ore-pass dewatering shafts and rare conveyor declines. The duct specification leans heavily to surface galvanized rectangular and round duct, dust collection at crushers and screens, and process exhaust from concentrators.

Olympic Dam in South Australia is the inverse case. BHP operates one of the world's largest underground polymetallic mines (copper, uranium, gold, silver) at Olympic Dam, with a sub-level open-stoping operation and a uranium hydrometallurgy circuit on surface. The underground ventilation network handles diesel haulage trucks, loaders and development jumbos at depth, with dedicated radon ventilation criteria layered on top of conventional DPM and heat targets. Surface HVAC includes the SX (solvent extraction) acid mist circuit and the smelter — both calling for 316 stainless duct, welded seams and chemically resistant gaskets.

The Cobar and Broken Hill base-metals districts in NSW host underground zinc-lead-silver and copper-gold operations — Endeavor, CSA, Rasp, Hera and others — typically narrower-vein operations with heavy reliance on auxiliary fan ventilation in development headings. The duct specification here is dominated by anti-static fabric flexible duct, helical-spring secondary returns and short rigid main lines.

The Kalgoorlie-Boulder gold belt and the Wiluna-Leinster nickel belt in Western Australia are the deepest operations in the country — KCGM Super Pit transitioning to underground at Mount Charlotte, Northern Star's Kanowna Belle and Jundee, BHP's Nickel West underground portfolio. Heat is the controlling pollutant in many of these mines, with virgin rock temperatures over 50°C at depth and refrigerated ventilation systems supplying chilled air through insulated steel duct.

The NSW Hunter Valley and Illawarra coal basins, and the Bowen Basin in Queensland, host the country's coal mines — both surface and underground. Underground coal is a different regulatory universe altogether: every electrical and mechanical component in the ventilated workings must be Ex-rated to AS/NZS 60079, every duct run must be designed against methane layering and inrush, and every refuge bay must be 36-hour rated against fire and explosion atmospheres. Operators include Glencore, Anglo American, Whitehaven, BHP Mitsubishi Alliance, Yancoal, Centennial and Peabody. Auxiliary fan flexible duct in coal is anti-static rated, terminations are Ex-certified and the entire circuit is audited against the relevant state Coal Mining Safety and Health Regulation.

Mining ventilation regulators and standards

Mining ventilation HVAC is one of the most heavily regulated subdomains in industrial engineering, and the regulator stack determines almost every duct specification decision. The standards apply at three levels: federal mining safety regulation, state-by-state mining regulator (in Australia, mining is administered at state level), and underlying engineering standards.

Australian state mining regulators

• NSW Resources Regulator — administers the Work Health and Safety (Mines and Petroleum Sites) Act 2013 and Regulation 2014. Underground ventilation officers must hold a NSW Mine Ventilation Officer certificate of competence. Refuge bays, principal hazard management plans and trigger action response plans are mandated. Mine air sampling and statutory return reports are filed against the Mine Air Sampling Scheme (MASS).
• Resources Safety & Health Queensland (RSHQ) — administers the Coal Mining Safety and Health Act 1999 and Regulation 2017 for coal, and the Mining and Quarrying Safety and Health Act 1999 for metalliferous. Coal ventilation requirements are among the most prescriptive in the world — methane drainage, ventilation flow, gas monitoring, refuge bay design and inrush management are all explicit. The Queensland Resources Industry Mineworker Authentication (RIMA) framework governs ventilation officer competence.
• WA DEMIRS (Department of Energy, Mines, Industry Regulation and Safety) — administers the Mines Safety and Inspection Act 1994 and the Work Health and Safety (Mines) Regulations 2022 (transitioning). Resources Safety in WA is the dominant regulator for the Pilbara iron ore, Goldfields gold and northern nickel operations. Heat stress management, refrigerated ventilation and DPM exposure rules are well established.
• NT Department of Industry, Tourism and Trade — administers mining safety in the Northern Territory across base-metals (McArthur River) and uranium (Ranger, Jabiluka) operations.
• SA Mining Regulation Branch (Department for Energy and Mining) — covers Olympic Dam, Prominent Hill, Carrapateena and the Eyre Peninsula iron operations.

International mining safety regulators

• MSHA (United States Mine Safety and Health Administration) — 30 CFR Parts 56, 57, 70, 75 and 90. Part 70 sets the Total Carbon (formerly Elemental Carbon) limit for diesel particulate matter at 160 micrograms per cubic metre. Part 75 governs underground coal ventilation including methane and respirable dust limits. Australian operators benchmark to MSHA on multinational sites.
• SAMRASS (South African Mineral Resources Administration Statistical System) — South African deep gold and platinum mines are the global benchmark for refrigerated ventilation engineering at depths beyond 3,000 metres.
• DGMS (Directorate General of Mines Safety, India) — Indian coal and metalliferous mining regulator with prescriptive ventilation and refuge bay rules.
• ICMM (International Council on Mining and Metals) — voluntary industry framework whose Mining Principles cover ventilation, occupational health and emergency preparedness.

Engineering and product standards

• AS/NZS 1668.4 — mechanical ventilation for acceptable indoor air quality, applied to mine surface buildings, control rooms, accommodation and processing.
• AS/NZS 1668.1 — fire and smoke control in buildings, applied to surface plant and refuge bay smoke isolation.
• AS/NZS 4254 — ductwork for air-handling systems in buildings (Parts 1 and 2), the duct construction class reference for fabricators.
• AS 4260 — high-efficiency particulate air filters and dust collection.
• AS/NZS 60079 series — explosive atmospheres, equipment classification (Ex), the Australian adoption of IEC 60079.
• ISO 19433 — ventilation engineering for refuge bays and chambers, applied to sealed duct integrity testing.
• ICMM mining safety guidelines — voluntary best practice across heat, DPM, dust and refuge bay topics.
• SMACNA HVAC Duct Construction Standards — North American duct fabrication reference, often cited on multinational mining contracts.

Underground vs surface HVAC duct — two distinct domains

Underground and surface mining HVAC are different enough that treating them as a single duct specification is the most common procurement mistake we see. They share the same coil stock and the same fabrication machines, but the airflow regime, sealing standard and material protection differ.

Underground: high-velocity main circuits, auxiliary face delivery

Underground mine HVAC is dominated by main intake and return airways carrying tens to hundreds of cubic metres per second across kilometres of declines, levels and ventilation raises. The bulk of that air moves through the rock excavation itself — the drift, decline or shaft is the duct. Engineered HVAC ductwork comes in at three points:

• Auxiliary fan ducting carrying air from a main intake to a development face — typically 600 mm to 1,500 mm diameter, 100 to 1,500 metres long, fabric or rigid steel depending on velocity and life.
• Refuge bay supply ducting — sealed steel ductwork delivering breathable air at positive pressure.
• Targeted exhaust ducts — for example, a stope ventilation drop line, or a controlled-flow line carrying dust-laden return from a crusher chamber.

Velocity in auxiliary fan rigid duct typically runs 12 to 20 metres per second, well above the 6 to 10 metres per second regime of building HVAC. Friction losses are correspondingly higher. The duct must hold tightness against full fan delivery pressure (often 2.5 to 6 kPa for development fans), survive blast pressure pulses without joint failure and resist abrasion from grit-laden return air.

Surface: processing exhaust, dust collection, building HVAC

Surface mining HVAC covers the processing plant — crushers, mills, screens, flotation cells, leach tanks, smelters, refineries — plus control rooms, workshops, accommodation and laboratories. Velocity, pressure and material specifications match conventional industrial HVAC much more closely. AS/NZS 1668.4 is the dominant indoor-air-quality reference for occupied spaces. Process exhaust ductwork is dictated by the chemistry of the offgas:

• Crusher and screen-house dust collection — galvanized G275 spiral round duct, capture velocity 18 to 25 metres per second at the hood, transport velocity above 18 metres per second to prevent settlement.
• SAG/ball mill ventilation — moisture and abrasive dust, typically galvanized rectangular with stainless-lined elbows.
• Flotation cell exhaust — frothing reagents are corrosive, FRP or 316 stainless duct.
• SX/EW (solvent extraction / electrowinning) — sulphuric acid mist in the cell-house atmosphere, 316 or duplex stainless mandatory, welded seams, chemically resistant gaskets.
• Smelter offgas — pyrometallurgical operations produce acidic and corrosive offgas; primary capture is refractory-lined steel into the gas-cleaning train; final stack is welded stainless or carbon steel with corrosion-resistant lining.
• ROM bin enclosures and conveyor transfer points — galvanized rectangular duct with abrasion-resistant ceramic-tile lining at high-wear zones.

Methane management in coal mines

Methane is the controlling pollutant in every Australian underground coal operation. The Coal Mining Safety and Health Regulation 2017 in Queensland and equivalent NSW provisions set explicit limits — typically a working-place general body limit of 1.25 percent methane, with action triggers and withdrawal points at higher concentrations. The ventilation system is designed first to keep methane below the working limit, and only after that is it sized for diesel exhaust, dust and heat.

The HVAC duct architecture in coal addresses methane in three ways:

• Bulk dilution by the main ventilation circuit — large-volume airflow through the longwall and panel returns, with primary fans on surface drawing return air through ventilation shafts. Duct is typically integral to the rock excavation itself, with engineered duct only at fan inlet/outlet plenums and surface stack.
• Auxiliary fan ventilation in development headings — anti-static fabric flexible duct delivering fresh air to the development face, sized so the local methane concentration at the face never approaches the lower explosive limit. Anti-static specification is critical because electrostatic discharge from fabric can ignite a methane layer.
• Methane drainage piping — separate from ventilation duct, but related. Methane drainage uses sealed steel pipework to draw concentrated methane from the goaf, longwall face or pre-drainage holes for venting or capture. Pipework is typically 100 mm to 600 mm diameter, often welded steel, with intrinsically safe gas monitoring at every junction.

Every electrical and mechanical component in the coal mine ventilated zone must be certified to AS/NZS 60079 (the Australian adoption of IEC 60079) or the equivalent ANZEx scheme. Fan motors are Ex d (flameproof enclosure), pressure transducers and gas monitors are Ex i (intrinsically safe), and any duct-mounted instrumentation carries an Ex certification with a documented zone classification. The duct itself, being passive steel or anti-static fabric, does not require Ex certification — but every connector and every electrical termination does.

Diesel particulate matter (DPM) in metalliferous mines

DPM is the controlling occupational health pollutant in most underground metalliferous mines. The MSHA reference under 30 CFR Part 70.260 sets a Total Carbon limit of 160 micrograms per cubic metre as a personal exposure limit; Australian benchmarks track this closely with Safe Work Australia exposure standards and state-by-state operator targets. The ventilation engineer of record sizes airflow against the controlling pollutant — which is often DPM in a diesel-dominated mine, until depth pushes heat into first place.

DPM dilution airflow is computed from installed diesel power, equipment duty cycle, an emission factor in mass per kilowatt-hour and the target concentration. Australian metalliferous practice is broadly 0.06 to 0.07 cubic metres per second of fresh air per kilowatt of installed diesel power for primary haulage and loader equipment, scaled upward for confined headings and for older non-Tier 4 engines. The ventilation engineer applies the regulator-mandated ratio, then verifies the design against measured DPM at the working face during commissioning.

From the duct designer's perspective, DPM dilution is a volumetric airflow target, which in turn sets the duct cross-section. A development heading running a Tier 4 jumbo (110 kW), a loader (240 kW) and a haul truck shuttle (300 kW) drives a fresh-air target of 40 to 50 cubic metres per second, which sets the auxiliary fan duct at 1,400 to 1,600 mm diameter at 22 to 25 metres per second velocity. Over-specifying the duct adds material cost; under-specifying generates a regulator-flagged exposure exceedance and a stop-work order.

Heat stress management in deep mines

At depth, the geothermal gradient turns rock into a heat source, and machines are heat sources, and humans are heat sources. Australian deep operations — Mount Isa, Cadia East, Olympic Dam at depth, Mount Charlotte, Jundee, Sunrise Dam — frequently encounter virgin rock temperatures of 40°C to 55°C. Without engineered heat removal, working faces become unsurvivable.

Wet-bulb globe temperature (WBGT) is the metric. ICMM and ACGIH reference around 28°C wet bulb as a tolerance limit for moderate work, with continuous tolerance dropping rapidly above 30°C. Australian operators typically engineer for 27°C wet bulb at the face on the design day to leave a margin. The ventilation system delivers heat removal in three layers:

• Bulk ventilation cooling by surface ambient air — adequate when surface ambient is below 20°C wet bulb. Pilbara summer surface ambient frequently exceeds this, eliminating bulk cooling as the only mechanism.
• Mechanical refrigeration of intake air — surface or underground refrigeration plant chilling either the air directly (bulk air cooler) or chilled water that exchanges into the airstream at sub-surface positions. Chilled-water duct in mining context is insulated steel pipework, but the air-side heat exchanger ducts the cooled air through insulated steel rectangular or round duct from the cooler outlet to the working district.
• Local spot-cooling and personal cooling — for very deep operations where bulk cooling cannot reach the face economically, refrigerated personnel-cooling rooms are positioned within walking distance of the face.

The duct specification implications are significant. Insulated rectangular or round ductwork carrying chilled air at 8 to 12°C through a mine with a 35°C drift atmosphere will condense heavily — every joint must be sealed against liquid water ingress and egress, every low point needs a trapped condensate drain, and the insulation system must be specified for the ambient dew point. Galvanized steel is the standard substrate, with foam-glass or polyurethane insulation and a vapour-tight outer skin.

Auxiliary fans and flexible ducting

Auxiliary fans are the workhorse of underground mine HVAC. Every development heading — drift, raise, decline, sub-level access — gets a dedicated auxiliary fan installed at the entrance to the heading from a fresh-air intake, with flexible or rigid duct delivering air to the working face.

Lay-flat and helical-spring fabric duct

Fabric flexible duct is the dominant choice for development headings in Australian operations because it ships compactly, hangs from a continuous suspension wire and adapts to advancing face position. Two construction types are common:

• Lay-flat (forcing) duct — pressurised by the auxiliary fan upstream, the duct holds shape under positive pressure. Typically PVC-coated polyester fabric, with a continuous longitudinal seam and fixed reinforcement bands. Diameters from 400 mm to 1,500 mm, lengths up to 100 metres per section. Connection at the fan and at section-to-section joints uses cuff-and-strap or zip-and-velcro arrangements rated for the design pressure.
• Helical-spring (exhausting) duct — under negative pressure, fabric duct collapses without internal support, so a continuous helical spring of plastic or galvanised wire holds the cross-section. Typical for return-air drainage from a stope or face exhaust. Diameters from 300 mm to 1,200 mm, lengths up to 50 metres per section. Connection uses cuff-and-strap, sometimes flanged for high-pressure exhaust.

For coal applications, the fabric specification adds anti-static and flame-retardant requirements per the relevant Coal Mining Safety and Health Regulation. Surface resistivity must be below 10⁹ ohms; the duct must self-extinguish within seconds of removing an ignition source. Recognised manufacturers (Korfmann, Spiroflex, Protan, ABC Industries, Krempel) all offer coal-mine-specification ranges; the specifier verifies certification documents against the regulator's accepted testing list.

Rigid duct for long runs and high-pressure applications

For long auxiliary runs (above 500 metres), high-static-pressure development (above 3 kPa fan delivery) or installations with a long economic life (more than 24 months), rigid duct displaces fabric. Steel spiral round duct, fabricated on a tubeformer from galvanized G275 coil, is the dominant rigid format for auxiliary fan duty. Diameters 600 mm to 1,500 mm, lengths in 6-metre sections joined with bell-and-spigot or flanged couplings, suspension at 3-metre intervals from rock bolts.

The friction coefficient of spiral steel is significantly lower than fabric, so for the same airflow target the fan static pressure is lower and the energy consumption over the life of the installation is meaningfully reduced. The trade-off is upfront cost, installation time and the need to re-route the duct as the face advances. Most operations adopt a hybrid — rigid steel for the first 200 to 500 metres of the heading, fabric extension to the face that is rolled forward as development advances.

Rigid duct in mining: main intake/return drifts, refuge chambers, decline portals

Rigid steel ductwork shows up in mining HVAC in several distinct architectures, each with its own specification.

Main intake and return drifts

The main air-handling capacity of a mine moves through the excavation itself, but where the geometry needs engineered ductwork — at fan plenums, surface intake portals, ventilation raise transitions — the duct specification is heavy-gauge rectangular or round steel, designed for fan static pressure and survivability through blast pressure pulses. Galvanized G275 steel 1.6 to 3.0 mm wall thickness, longitudinal Pittsburgh seam for rectangular or lock-formed for round, flanged or welded transverse joints, gasketed for low leakage. Suspension by structural steel hangers at 1 to 3 metre spacing. The duct survives the design life of the mine — typically 20 to 50 years — so corrosion protection, joint integrity and replaceability of failed sections are all considered at design stage.

Refuge chambers

Refuge bay supply ductwork is a distinct sub-category that we cover in detail in the next section. It is rigid, sealed, pressure-tested and gas-tightness certified.

Decline portals and surface fan plenums

Where the mine accesses surface — at the decline portal, the ventilation raise collar, the workshop bay door — the duct architecture transitions from underground ventilation to surface HVAC. Decline portal coverings, surface fan plenums and weather hoods are typically rigid galvanized sheet duct with weatherproof gasketing, animal exclusion screens and bird control. Where the surface fan exhausts to atmosphere, a stack with rain hood, lightning protection and aviation marker lighting completes the assembly.

Refuge bay HVAC — positive pressure isolation, breathable air, sealed duct integrity

The refuge bay is the single most critical safety-rated HVAC asset in an underground mine. It is the chamber to which workers retreat during a fire, explosion, inrush or atmospheric event, and survival depends entirely on the integrity of the chamber envelope and the breathable air supply.

The HVAC architecture is a positive-pressure compartment with:

• An external sealed steel duct delivering breathable air from a remote source — typically the mine compressed-air reticulation, a dedicated bulk-air-cooler take-off or a redundant compressor.
• An internal regulator damper or pressure-controlled inlet that maintains chamber overpressure between 50 and 200 pascals relative to mine atmosphere.
• A stale-air discharge with a non-return valve so chamber air exhausts to mine atmosphere but mine air cannot back-flow in.
• A blast valve or overpressure relief on the supply line to handle explosion-driven pressure transients without rupturing the duct.
• Continuous gas monitoring (CO, CO₂, O₂, NO₂) inside the chamber and at the supply intake, with isolation logic if external air becomes contaminated.

Duct integrity is verified by pressure-decay testing during commissioning and at a regulator-mandated frequency thereafter. Australian operators typically run an annual pressure-decay re-test on the chamber envelope including the supply ductwork. Duct construction is welded steel longitudinal seams (not Pittsburgh slip-and-drive, which leaks), flanged or welded transverse joints with full-face gaskets, and pressure-rated isolation valves at the chamber boundary. Stainless steel is increasingly common in operations with corrosive groundwater because failure of the supply duct during an emergency would defeat the chamber.

ISO 19433 sets out chamber pressure profiles, breathable air supply rates (typically 1 cubic metre per minute per occupant minimum) and integrity testing requirements. Australian mines reference ISO 19433 alongside the relevant state mining safety regulation for chamber sizing — typical specifications are 12-hour, 24-hour or 36-hour endurance, with hard-rock metalliferous mines often specified at 24 hours and coal mines at 36 hours minimum.

Ventilation On Demand (VOD)

Primary fan electrical consumption is one of the largest single utility costs at most underground mines — frequently 30 to 50 percent of total site electricity. Ventilation On Demand (VOD) is the automated control of mine airflow to actual demand, replacing the historical practice of running fixed nameplate airflow at all times regardless of where equipment and personnel are working. Energy savings of 25 to 50 percent on primary ventilation are typical, with payback periods often under three years.

Two architectures are common, and most mature systems combine them:

• Fan-based VOD — variable-frequency drives on primary and auxiliary fans modulating fan speed to match real-time airflow demand. Demand signals come from RFID/Wi-Fi tags on equipment, scheduled production plans and gas monitoring.
• Damper-based VOD — motorised regulator dampers in branch ventilation circuits, opening for active districts and closing for inactive ones. The primary fan runs at a fixed efficient operating point and the dampers redirect air.

From the duct specification perspective, VOD imposes additional requirements on the rigid duct circuit:

• Low-leakage construction — leakage at branch take-offs destroys VOD economics, so duct seams must be sealed (not just slipped), flanged joints fully gasketed and damper bodies specified for low seat leakage at the closed position.
• Motorised regulator dampers sized for full open-area at design flow with damper-tight sealing at zero flow, position feedback to the mine ventilation control system, and full-stroke 0 to 100 percent control.
• Pressure transducer tappings on branch ducts so the control system has real-time pressure data for closed-loop regulation.
• Communications backbone in Ex-rated cabling (intrinsically safe or fibre-optic) to the dampers and transducers.

Australian operators with mature VOD systems include Glencore's CSA Mine, Rio Tinto's Argyle (now closed) and several deep gold operators. The retrofit market for existing mines is substantial — replacing legacy duct branches that leak heavily with sealed, instrumented duct is often the largest single capex item in a VOD upgrade.

Surface mining and processing HVAC

Surface mining HVAC scope is dominated by the processing plant. The duct specification follows the chemistry and the dust loading.

Crusher and screen-house dust collection

Primary, secondary and tertiary crushing stations generate enormous dust loadings. Capture velocity at the hood is 18 to 25 metres per second, transport velocity in the duct is 18 to 22 metres per second to prevent settlement, and the duct system terminates at a baghouse or scrubber. Galvanized G275 spiral round duct is the workhorse, with abrasion-resistant elbows (chrome carbide overlay or ceramic-tile lined) at high-wear bends. Branch take-offs use 30-degree wyes rather than tees to maintain transport velocity.

Mill and concentrator ventilation

SAG and ball mill enclosures are vented for moisture and abrasive dust control. Galvanized rectangular duct with stainless-lined elbows is typical. Flotation cell exhaust adds frothing reagents to the airstream — corrosive enough to require FRP, lined steel or 316 stainless duct depending on the specific reagent chemistry.

SX/EW and acid-mist systems

Solvent extraction and electrowinning circuits in copper and nickel hydrometallurgy generate sulphuric acid mist in the cell-house atmosphere. Ductwork is 316 or 2205 duplex stainless, welded longitudinal seams (Pittsburgh seams leak acid mist into the worker breathing zone), TIG or pulsed-MIG procedures, full-face gaskets specified for the acid duty (Viton or PTFE), and a mist eliminator upstream of the fan. Olympic Dam SX is a flagship Australian example — the cell-house ductwork there is multi-hundred-tonne stainless fabrication, replaced on a 10 to 15 year cycle.

Smelter offgas

Pyrometallurgical smelter offgas (Olympic Dam, Tomago Aluminium, Bell Bay, Mount Isa) is one of the most demanding HVAC duct applications anywhere in industrial engineering. Primary capture is refractory-lined steel into the gas-cleaning train, with the offgas at 800°C to 1,400°C. The gas-cleaning train (electrostatic precipitator, gas cooler, scrubber) reduces temperature and acidity, and the post-clean stack is welded carbon steel or stainless with corrosion-resistant lining or coating. Stack design references AS 1170 wind loading, AS 4100 steel structures and the specific smelter operator's offgas chemistry.

ROM bin enclosures and conveyor transfer points

Run-of-mine ore bins, conveyor transfer points and stockpile reclaim feeders all generate dust at material drop. Enclosure ventilation captures the displaced air through ductwork to a baghouse. Galvanized rectangular duct is typical, with abrasion-resistant ceramic-tile lining at points where ore pieces could impact the duct wall. Negative-pressure design ensures dust is captured rather than escaping into the work area.

Control rooms and accommodation

Control rooms, maintenance workshops and mine accommodation use conventional surface HVAC against AS/NZS 1668.4 outdoor air rates. Duct specification is unremarkable galvanized rectangular and round. The complication on remote sites (Pilbara, Goldfields) is that everything is shipped to site as a complete fabrication, since mobilising a duct shop to a fly-in fly-out site is uneconomic. Pre-fabrication relies on accurate site survey and dimensional control on the fabrication shop floor.

Cooling coil and condensate management in deep mines

Refrigerated ventilation in deep mining creates a moisture management problem that surface HVAC engineers rarely encounter. Chilled supply air at 8 to 12°C running through a mine atmosphere at 32 to 40°C dry bulb and high relative humidity will condense heavily on the duct outer surface and inside the duct at any cool spot. Without engineered drainage, the duct becomes a rolling pool that floods refuge bays and electrical equipment downstream.

Design strategies include:

• Insulation outboard of the duct skin — closed-cell foam, foam-glass or polyurethane with a vapour-tight outer skin (typically PVC or aluminium jacket). The duct outer surface is held above dew point so external condensation is eliminated.
• Trapped drains at every low point — internal condensation collects at duct sags, low points and elbow inverts. Trapped drain ports drain to the mine pump system. Drain spacing is typically every 10 to 20 metres on a downhill run.
• Sloped duct geometry — supply ducts are installed with a continuous slope to direct internal condensate to drainage points. Designing the duct routing with drainage in mind from the outset is much cheaper than retrofitting drains.
• Cooling coil drain pans — the cooling coil itself produces the largest condensate stream. Stainless steel drain pans with trapped, sized drainage to the mine sump are mandatory. Pan capacity is typically sized for 60 minutes of continuous condensate at design conditions.

Failure modes worth flagging: a flooded refuge bay supply duct delivers contaminated water into the chamber atmosphere and can defeat positive pressure. A flooded VOD damper body can seize the actuator. A flooded pressure transducer tapping reports false low pressure and triggers fan over-speed. Drainage is not optional.

Mine emergency response — fire, explosion, smoke control

The HVAC system is part of the mine emergency response system. AS/NZS 1668.1 sets out smoke control duct integrity in buildings, and the principles transfer to surface plant and refuge bay isolation. Underground emergency response is governed by the relevant state mining safety regulation, with operator-specific principal hazard management plans.

Emergency duct specifications include:

• Fire-rated isolation dampers between refuge bay supply ductwork and the mine atmosphere, capable of closing within seconds on fire alarm signal and holding integrity through the chamber endurance period.
• Reversible main fan capability where the mine plan requires it — surface fans that can switch from forcing to exhausting within minutes to clear fire smoke from the mine workings.
• Blast valves on refuge bay supply lines to handle methane explosion overpressure transients without rupturing the duct or breaching the chamber.
• Smoke control duct seams welded or gasketed to the fire integrity rating — typically 60 minutes for surface plant and chamber endurance for refuge bay supply.
• Self-rescuer cache locations and breathable air drop points along egress routes, with sealed steel reticulation duct.

Material specifications — coil, coating, alloy

Material selection is the largest single lever on duct life and total cost of ownership. The default choices and the upgrade triggers:

Galvanized steel (G275, G350)

Hot-dip galvanized coil is the workhorse for normal underground service and for surface plant in low-corrosion environments. Coating mass is specified by the G grade — G275 means 275 grams per square metre total (both sides combined), G350 means 350. AS 1397 is the Australian standard for continuously hot-dip metallic coated steel. For most underground mining HVAC duty, G275 is the baseline; for surface processing exposure to mild corrosion, G275 to G350; for extended-life surface assets, G450 or G500.

Coil thickness for mining duty is typically 0.6 mm to 1.6 mm for spiral round duct and 0.7 mm to 2.0 mm for rectangular fabricated duct. Heavier gauges go on main intake/return drifts and refuge bay supply.

Hot-dip galvanized after fabrication

Where the operating environment is more corrosive than coil galvanized can survive — acid mine drainage, hypersaline brines, high-chloride atmospheres — hot-dip galvanizing the fabricated duct after seam welding gives a thicker, more uniform coating that covers the seam. Coating mass is typically 600 to 800 grams per square metre. Limitations include duct dimensional tolerances after the dip (the high heat warps thin gauges) and dimensional limits of the available galvanizing tank. Most Australian galvanizing tanks accept duct sections up to 12 metres long.

Epoxy-coated steel

For corrosive environments where hot-dip galvanizing is not viable — typically because of dimensional or weight constraints — epoxy coating gives an alternative protection layer. The epoxy is typically applied as a powder coat, electrostatically deposited and oven-cured. Coating thickness is 250 to 500 micrometres. The trade-off is impact damage during installation can expose bare steel and become a corrosion initiation point; specifying with cathodic protection at exposed edges is good practice.

304 and 316 stainless steel

Stainless is mandatory for processing acid environments. 304 stainless (18Cr-8Ni) is adequate for low-chloride mild acid duty; 316 stainless (16Cr-10Ni-2Mo) handles moderate chloride and sulphuric acid mist; 2205 duplex (22Cr-5Ni-3Mo) handles higher chloride and stress-corrosion-cracking environments. Welding is GTAW (TIG) or pulsed-MIG with matching filler — autogenous welds without filler can suffer carbide precipitation and reduced corrosion resistance. Olympic Dam SX, Mount Isa Copper Smelter, Boddington gold and most modern hydrometallurgical circuits run 316 or duplex stainless ductwork.

Anti-static and flame-retardant fabric

For coal mine flexible duct, the fabric must be anti-static (surface resistivity below 10⁹ ohms) and flame-retardant (self-extinguishing within seconds of removing ignition source). Recognised manufacturers (Korfmann, Spiroflex, Protan, ABC Industries, Krempel) offer compliant ranges with documentation traceable to the relevant state mining regulator's accepted list.

Worked Australian mining HVAC examples

Olympic Dam underground expansion (BHP, South Australia)

Olympic Dam is one of the world's largest underground mines and a key Australian example of a complex mining ventilation HVAC system. The underground operation runs sub-level open-stoping at depth with diesel haul trucks, loaders and development jumbos. Ventilation airflow is in the range 1,500 to 2,500 cubic metres per second across the mine, with primary fans on surface drawing return air through ventilation shafts. The HVAC duct scope underground includes auxiliary fan flexible duct on every active development heading, refuge bay sealed supply ductwork on every chamber, and a network of regulator dampers for ventilation control.

On surface, Olympic Dam runs a uranium hydrometallurgy circuit and a copper smelter. The SX cell-house ductwork is multi-hundred-tonne 316 stainless fabrication with welded seams, full-face gaskets and acid-mist eliminators. The smelter offgas line is refractory-lined steel into the gas-cleaning train. Both circuits are flagship examples of mining HVAC engineered for very long service life under aggressive chemistry.

Cadia East panel cave (Newmont, NSW)

Cadia East is Australia's largest underground gold-copper operation and a panel-cave block-cave operation at depth. Ventilation circuit handles diesel equipment and the natural draft from cave subsidence. Refrigerated ventilation is in the design envelope as the operation deepens. The HVAC duct scope is typical of a deep block-cave operation — heavy-gauge rigid main ducts, instrumented regulator dampers for VOD, sealed refuge bay supply lines, and surface processing ductwork in the concentrator.

Mount Isa underground extension (Glencore, Queensland)

Mount Isa is one of the world's longest-running underground polymetallic operations, with copper, lead, zinc and silver in distinct ore systems. The underground ventilation circuit is one of the most complex in Australia, with multiple primary fans, sub-system fans and a heavily instrumented regulator damper network. Mount Isa was an early Australian adopter of Ventilation On Demand. The HVAC duct scope reflects the maturity of the operation — extensive sealed rigid duct on main circuits, comprehensive refuge bay coverage, and staged retrofits as production zones move through their life cycle.

Pilbara iron-ore processing plants (Rio Tinto, BHP, FMG)

The Pilbara iron-ore province is dominated by surface operations — open-pit mining, primary crushing, screening, train load-out. Underground HVAC is minimal. Surface HVAC scope is dust collection at every crusher, screen house, conveyor transfer point, train load-out station and stockpile reclaim feeder, plus building HVAC for control rooms, workshops and accommodation. The duct material specification is overwhelmingly galvanized G275 spiral round and rectangular, fabricated in regional duct shops in Karratha, Port Hedland or Perth and trucked to site. Lead time on a Pilbara crusher dust-collection package is typically 6 to 10 weeks from coil to commissioned.

Cobar and Broken Hill base-metals (NSW)

Cobar (Endeavor, CSA, Peak) and Broken Hill (Rasp, CBH) host narrow-vein underground operations with heavy reliance on auxiliary fan ventilation. The HVAC duct scope is dominated by anti-static fabric flexible duct on every development heading, with shorter rigid steel main lines and refuge bay supply. CSA Mine has been an Australian VOD pioneer, with instrumented regulator dampers throughout the active mine.

SBKJ machinery for mining HVAC fabrication

Most large mining contractors and mining-focused HVAC fabricators run a regional duct shop sized to one to three production shifts. The standard machinery package covers rectangular duct, round duct and welded stainless processing duct. SBKJ Group manufactures the full range from our Australian operation in Box Hill North, Victoria.

SBAL-V auto duct production line — surface processing rectangular duct

The SBAL-V is the high-output coil-fed auto duct production line, sized for 0.6 mm to 1.6 mm galvanized G275 coil up to 1,500 mm working width. In a single pass it cuts the coil to length, notches, beads, breaks and Pittsburgh-seams. Single-shift output is 800 to 1,200 metres of finished rectangular duct equivalent — sufficient for a regional mining duct shop running surface plant and crusher dust collection at full capacity. The line uses Siemens or Mitsubishi PLCs as standard, branded servo drives and CE-marked safety guarding to Machinery Directive 2006/42/EC. Full specification on the SBKJ auto duct lines page.

SBTF spiral tubeformer — high-volume underground rigid duct

The SBTF spiral tubeformer fabricates round duct from 100 mm to 1,500 mm diameter directly from G275 galvanized coil, with continuous spiral lock-formed seam. Output is 12 to 20 metres per minute depending on diameter and gauge, making it the right machine for the high-volume rigid duct demand of an active mine. The SBTF accepts 0.4 mm to 1.5 mm coil thickness and is configurable for stainless 304/316 with the appropriate roller set. Full specification on the SBKJ spiral tubeformer page.

SBAL-III general industrial line

The SBAL-III is the mid-output auto duct production line for shops that run a mix of mining surface processing duct, building HVAC duct and general industrial duct. Lower throughput than the SBAL-V but lower capital cost. Suitable for fabricators serving multiple end markets where mining is one of three or four verticals.

Duct welding stations for stainless processing fabrication

For 316 stainless and duplex stainless processing duct fabrication, SBKJ supplies longitudinal seam welding stations and TIG/MIG welding cells configured for stainless duty. The combination of an SBAL-V or SBAL-III for the rectangular forming, an SBTF for round and a stainless welding cell for the processing offshoot covers the full range a mining-focused fabricator will see in practice. Full specification on the SBKJ duct welding machines page.

For background on the material trade-offs see our companion guide galvanized vs stainless steel duct, the duct fittings fabrication guide and the welding methods reference.

Procurement and RFQ guidance for mining HVAC contractors

If you are issuing an RFQ for mining ventilation HVAC duct fabrication or for in-house duct shop machinery, the following procurement points concentrate the technical risk.

For fabricated duct (engineered procurement)

• Specify the controlling regulator (NSW Resources Regulator, RSHQ, WA DEMIRS) and the project's ventilation officer of record on the front page of the RFQ. Bidders use this to size their compliance documentation.
• Specify duct material to AS 1397 G grade for galvanized, or to grade and specification for stainless. Vague calls for "galvanized" without a G grade attract budget bids on G140 that will not survive Pilbara summer.
• Specify joint type — Pittsburgh, lock-formed spiral, TDF, DW/144 flange, welded longitudinal seam — with the AS/NZS 4254 construction class.
• Specify FAT requirements at the fabrication shop including longitudinal seam pressure decay, dimensional tolerance, coating thickness verification and welded joint integrity for refuge bay duct.
• Specify on-site leakage testing to SMACNA leakage class or AS/NZS 4254 equivalent.
• Specify ATEX/IECEx requirements for any duct-mounted instrumentation in zoned environments.
• Specify spare-parts and consumables continuity — gaskets, fasteners, damper actuators — for the design life of the asset.

For duct shop machinery (capital procurement)

• Sized against your typical metre-per-week throughput and your G275 coil supply.
• Configured for your local voltage and frequency (Australian 415V/50Hz).
• Branded PLC (Siemens, Mitsubishi, Delta) for global support availability.
• CE-marked to Machinery Directive 2006/42/EC, ISO 9001 quality system, FAT mandatory before shipment.
• 30/70 T/T or L/C at sight payment terms — never 100 percent prepayment.
• 1 to 2 supplier engineers on site for installation and commissioning, operator training included.
• One-year wear-parts kit, 10-year parts continuity guarantee in writing.
• Australia-based after-sales out of Box Hill North VIC — same time zone, same business day response.

Our companion guide HVAC Duct Machine Buyer's Checklist covers the full 47-point procurement verification used by SBKJ engineers when our customers ask us how to evaluate any HVAC duct machinery purchase.

Cross-vertical references

Mining is one of several heavy-industrial HVAC verticals SBKJ machinery supports. For background on adjacent applications:

• Cleanroom HVAC ductwork — pharmaceutical and semiconductor cleanroom duct, with mining-relevant overlap on processing laboratory ventilation and on the duct-leakage testing methodology.
• SBKJ Group in Australia — Australian operation in Box Hill North, Victoria, with a 12-hour engineer-led reply policy and same-time-zone after-sales support.

FAQ — mining ventilation HVAC ductwork

What standards govern HVAC ductwork in Australian underground mines?

The primary engineering standard for the air-handling and conditioning side is AS/NZS 1668.4, applied in conjunction with the relevant state mining safety regulator (NSW Resources Regulator, Resources Safety & Health Queensland, WA DEMIRS, NT Department of Industry, SA Mining Regulation Branch). Refuge chambers additionally reference ISO 19433 and ICMM mining safety guidelines. Coal operations layer the relevant Coal Mining Safety and Health Regulation on top.

What is the typical ventilation airflow per kW of diesel underground?

Australian metalliferous mines typically design for 0.06 to 0.07 cubic metres per second of fresh air per kilowatt of installed diesel power. The MSHA reference under 30 CFR Part 70.260 sets a Total Carbon limit of 160 micrograms per cubic metre that drives the airflow alongside heat and gaseous criteria. Final airflow is calculated by the ventilation engineer of record using the controlling pollutant.

What duct material is appropriate for underground mining?

For rigid main intake and return circuits in metalliferous mines, hot-dip galvanized G275 minimum is the baseline; for corrosive groundwater specify hot-dip galvanized after fabrication or epoxy-coated. For processing acid environments specify 316 stainless or duplex grades. Auxiliary fan flexible ducting is anti-static PVC-coated polyester for development headings and helical-spring polyester for return circuits.

How does refuge bay HVAC differ from normal mine ventilation?

Refuge bays are positive-pressure compartments isolated from the mine atmosphere. Sealed steel ductwork delivers compressed breathable air at 50 to 200 pascals overpressure to prevent ingress of CO, NO2 and smoke. The supply line is welded or flanged steel, incorporates blast valves and isolating dampers tested to ISO 19433. Most Australian operators specify 12 to 36-hour rated chambers.

Do auxiliary fan duct lines need ATEX or IECEx certification in Australian coal mines?

Yes. Australian coal mines are zoned under AS/NZS 60079. Equipment in zones with potential methane atmospheres must be certified to IECEx or ANZEx. Fan motors, electrical controls and duct-mounted instrumentation require Ex d, Ex i or Ex p certification. Ductwork itself is passive and does not require Ex certification, but anti-static fabric specifications apply to flexible ducting in coal headings.

What is Ventilation On Demand and how does it affect duct design?

VOD is the automated control of mine airflow to actual demand. Two architectures are common: VFD control of fans and motorised regulator dampers in branch headings. Energy savings of 25 to 50 percent are typical. Duct design implications include sealed low-leakage rigid duct, motorised damper bodies sized for full open-area at design flow with damper-tight closed-position sealing, and pressure transducer tappings on branch ducts.

What are typical lead times for mining HVAC duct from an Australian-based supplier?

Standard fabricated rigid duct in G275 galvanized is typically 4 to 6 weeks for orders under 5,000 metres equivalent, 8 to 10 weeks for larger contracts. Stainless steel processing duct runs 6 to 10 weeks. Refuge bay sealed duct assemblies typically need 8 to 12 weeks because of the additional QA hold points. Plan procurement against the mine commissioning critical path.

How do I specify HVAC duct machinery for our own in-house mining duct fabrication shop?

Standard package is an SBAL-V or SBAL-III auto duct production line for rectangular duct (G275 galvanized 0.6 to 1.6 mm), an SBTF spiral tubeformer for round duct from 100 to 1,500 mm diameter, and a duct welding station for stainless processing fabrication. The SBAL-V is the primary workhorse. An SBKJ engineer will size the line against your throughput, coil supply and compressed-air capacity, and supply a layout drawing as part of the quotation.

Talk to an SBKJ engineer about your mining HVAC duct project →