Mining & Minerals

Mining puts people into atmospheres that change hour by hour. A heading that was clear at the start of a shift can hold enough carbon monoxide to kill by the end of it. A stope that has ventilated overnight can release a pocket of gas the moment the ore pile is disturbed. A gold room that has run without incident for a decade can expose an operator to mercury vapour they cannot see or smell.

Gastech has supplied gas detection to Australian mining since 1978, and most of what follows comes from work our engineers have done on site.

The Monthly Ventilation Survey

Underground ventilation is a system, and like any system it needs measuring rather than assuming. Fresh air enters through intake shafts or adits. Used air carrying dust, gases and heat leaves through exhaust shafts or rises. Auxiliary fans and vent bags push air into dead ends such as development headings and stopes where the primary circuit does not reach.

Most Australian mines verify that monthly through what is generally called the Ventilation Primary Survey. A ventilation engineer or technician visits a set of predetermined locations and records gas concentrations, airflow and temperature at each. The gases surveyed come from the mine’s own gas risk management chart, built from local geology and the extraction processes in use.

In hard rock the common set is oxygen, LEL, carbon monoxide, hydrogen sulphide, nitrogen dioxide and ammonia, with carbon dioxide, sulphur dioxide and chlorine appearing less often. That means a survey instrument needs six or more channels and has to survive being carried through a working mine, which is why the five plus gas portables are the usual choice. Fixed detection covers the locations where risk is known and constant, and the survey confirms everything between them.

Post Blast Re-Entry

Re-entry is where the gas risk underground is most concentrated and most misunderstood.

After firing, nitric oxide is produced in volume and converts rapidly to nitrogen dioxide as it takes up an additional oxygen atom. Carbon monoxide is also present in quantity and is usually the last gas to disperse. Re-entry times are calculated on the expectation that ventilation has diluted both to safe levels, and whether those times are based on short term exposure limits or eight hour averages changes the answer considerably. A development heading will often clear within 45 minutes against a time weighted average, and take well over an hour where ventilation is poor.

Two gases appear that many risk assessments miss.

Where a pasted area is blasted with ANFO, the reaction with the cementitious fill can generate high concentrations of ammonia. Crews expecting carbon monoxide and nitrogen dioxide will not be carrying a sensor for it.

Where the orebody is highly sulphurous, sulphur dioxide can be present. That is not only a health hazard, it is evidence a sulphide dust explosion has occurred, which is a reportable event to the regulator in some jurisdictions including Western Australia. A detector configured for SO2 is doing compliance work as well as protecting the crew.

One practical detail is worth designing around. Re-entry crews typically arrive in a light vehicle, hold a portable multi-gas detector out of the window and drive into the heading to assess levels before dismounting. The inspection that follows includes washing down the walls to remove dust and debris, and that washing can release further pockets of gas. Detection has to stay with the crew throughout, not only at the point of entry.

Blind Stopes And Cracking The Brow

A blind stope is the case where ventilation cannot help you.

Post blast gases can sit trapped behind the ore pile itself, in a void the ventilation circuit does not reach. The atmosphere in the open drive tests clean while a significant volume of gas waits behind the muck pile. It is released when the ore is moved, an event miners call cracking the brow.

That makes bogger operators a specific exposure group. The gas set matches re-entry, with methane appearing where organic matter has decomposed into underground pockets, and oxygen displaced by whatever has been generated. Detection belongs both on the machine and in the operator’s hand, because the release is triggered by the equipment and experienced by the person. The Gastech G-Shield Fire was designed for the vehicle mounted half of that.

Refuge Chambers

A refuge chamber is a sealed vessel designed to keep people alive for up to 36 hours while a hazard is dealt with or a rescue mounted.

Because it is sealed, its atmosphere degrades predictably. Occupants exhale carbon dioxide and consume oxygen, and carbon monoxide can accumulate. Chambers carry compressed air, CO and CO2 scrubbers and oxygen candles to manage that, but those resources are finite. AS 1715:2009 requires the oxygen supplied to sit no lower than 19.5 percent and no higher than 22 percent.

Detection inside a chamber is resource management as much as safety. Occupants who cannot see their atmosphere will consume scrubber capacity and oxygen candles they do not yet need. Both portable instruments and detector tubes are used, with tubes offering a shelf stable option that does not depend on a battery having survived months of standby.

Drilling

Reverse circulation drilling creates a specific and underestimated risk. The technique combines high pressure air with a vacuum action at the head to return cuttings, which means subsurface gas can be brought rapidly and directly into the work area.

Methane is the most commonly encountered, released when coal seams, carbonaceous shales or organic rich sediments are intersected. Hydrogen sulphide comes from sulphide mineralisation and sedimentary environments, produced by bacterial sulphate reduction or liberated when sulphide bearing strata are disturbed. Carbon monoxide accumulates from diesel engines, compressors and generators on the rig, particularly in low wind or where equipment is poorly maintained. Nitrogen and other inert gases can produce oxygen deficient atmospheres.

Risk varies with geology, depth, groundwater, airflow and weather, which is why a pre-drilling assessment and continuous monitoring matter more than a fixed procedure. Detection sits both on the person and on the rig, and an area monitor covers the second of those. Most Australian drilling happens a long way from support, so instruments need to work without a service visit.

Coal, And The Damps

Underground coal has its own vocabulary, and it maps directly onto what needs detecting.

Firedamp is generally lighter than air, so it accumulates in unventilated workings and can issue from strata including the floor when barometric pressure falls. Blackdamp forms continuously as coal and timber oxidise. Fire stink is a warning rather than a hazard, and it is why experienced deputies still trust their nose alongside their instrument.

Diesel Particulate Matter

Diesel particulate matter is a different problem from gas and it needs different instruments.

DPM is the solid fraction of diesel exhaust: fine carbon particles with hydrocarbons from oils and lubricants adsorbed onto them, plus metals from engine wear. Particles agglomerate, sticking to each other and to larger airborne dust, and they travel on the ventilation flow well away from the vehicle that produced them.

The size is what makes it dangerous. Coarse particulate runs from PM10 down to PM5, fine particulate sits below PM2.5, and ultrafine and nanoparticles run from around 100 nanometres to below 50. At that scale particles penetrate deep into the respiratory system and enter the bloodstream. The World Health Organisation classified DPM as carcinogenic to humans in 2012 and placed it in its highest risk category, the same level as asbestos. Symptoms may not appear for twenty or thirty years.

Detection here means emissions analysis rather than gas detection, measuring particle count and mass concentration in the 15 to 70 nanometre range as well as across the PM fractions. Requirements vary between states, and in New South Wales filter compliance is addressed through MDG 29.

Gold Processing And Cyanide

Cyanidation is the standard route for gold, and the gas hazard it produces is not the reagent itself.

Ore is crushed and milled to a fine powder. Where sulphide content is high the ore is roasted at between 450 and 750 degrees Celsius, converting sulphides such as pyrite and pyrrhotite into less reactive oxides or sulphates, because sulphides would otherwise consume cyanide during leaching. Sodium cyanide is then added to the slurry, forming gold cyanide compounds.

Hydrogen cyanide is not deliberately produced. It forms as a by-product under certain conditions when contaminants in the ore react with cyanide compounds, and the reaction is made worse by rising temperature or pressure. Single gas HCN detection around leach tanks is about catching a process excursion early enough to adjust it, rather than waiting for an evacuation.

Heap leaching presents the same hazard through a different process. Ore is mixed with lime for pH control and stacked on lined pads, a weak cyanide solution is sprayed on and percolates through, and the pregnant solution drains to lined ponds for recovery. Yields are lower, around 60 to 70 percent, but the operation is far less labour intensive. HCN generation here is exacerbated by temperature or pH rather than pressure, and detection covers both operational areas and the pad perimeter.

Mercury In The Gold Room

This one catches operations by surprise, because mercury is not added to the process. It arrives in the orebody.

Mercury occurs naturally in many gold ores, particularly refractory sulphide ores, and it follows almost the same path as gold. Through the carbon in leach or carbon in pulp circuit it adsorbs onto activated carbon alongside the gold. During elution it desorbs with the gold and concentrates in the pregnant eluate, then carries through electrowinning into the smelting sludge.

Gold room furnaces run at 1,000 to 1,200 degrees Celsius. Mercury boils at 357. So any residual mercury volatilises instantly, and it is released into the gold room atmosphere at the point of smelting and during doré bar pouring.

Mercury vapour is colourless, odourless and gives no warning at hazardous concentrations. The Australian workplace exposure limit is 0.025 mg/m³, or 25 micrograms per cubic metre, as an eight hour time weighted average, which is a very low threshold to alarm against. Gastech supplies the Jerome J405 and the MVI Mercury Vapour Indicator for gold room monitoring.

WorkSafe WA Mines Safety Bulletin No. 147 found that gold room workers have been repeatedly exposed to elevated mercury levels and that atmospheric monitoring programmes are frequently inadequate. If your gold room has no mercury monitoring, that bulletin is the place to start.

Confined Space Entry

Tanks, vessels, hoppers, bins and underground structures on the surface are confined spaces, and entry is governed by AS 2865:2009. Atmospheric testing before and during entry applies on a mine site exactly as it does anywhere else in Australian industry, and the gases of concern follow the process rather than the industry.

Certification, And Why Group I Matters

Equipment taken underground into a coal mine has to be certified for it, and that is a different certification from surface industrial use.

Hazardous area certification splits into Group I for mining and Group II for surface industry. Most gas detection carries one or the other. A business running an underground operation and a surface processing plant will typically hold two sets of instruments, two sets of spares and two calibration procedures. The D-Guard², designed and built by Gastech, carries IECEx Ex ia I Ma for Group I alongside Ex ia IIC and IIB for Group II, plus ANZEx certification. One detector type covers both.

The standards that apply include AS 2290.3 for electrical equipment in coal mines, AS/NZS 60079.29.1 for the performance of flammable gas detectors, AS/NZS 60079.29.2 for their selection, installation, use and maintenance, and AS/NZS 4641. Instruments should be NATA calibrated, and field service capability matters as much as the certificate.

Who Regulates What

Mining safety in Australia is regulated at state level, not federally, and the three main mining states run genuinely different regimes. Anyone describing a single national mining gas detection requirement is simplifying.

In Western Australia the Work Health and Safety Act 2020 and the Work Health and Safety (Mines) Regulations 2022 took effect on 31 March 2022, replacing the Mines Safety and Inspection Act 1994 and its 1995 regulations. Air quality and monitoring sits in Chapter 10. The change was substantive rather than cosmetic, since most of the prescriptive requirements of the old regulations were deliberately replaced with a risk management duty on the mine operator. The regulator is WorkSafe WA, within the Department of Energy, Mines, Industry Regulation and Safety.

In New South Wales, mines and petroleum sites are regulated separately from general industry under the Work Health and Safety (Mines and Petroleum Sites) Act 2013 and its 2022 Regulation. The regulator is the NSW Resources Regulator rather than SafeWork NSW.

Queensland has not harmonised its mining safety legislation with the model work health and safety laws and runs separate coal and metalliferous regimes. The regulator is Resources Safety & Health Queensland.

For a national operator that means the same hazard can attract different obligations depending on the state. Gastech works across all three.

What Gastech Supplies To Mining

Portable gas detectors for personal monitoring, ventilation surveys, re-entry and confined space entry, in Group I certified form where the site requires it.

Fixed gas detection for known risk locations, ventilation returns, processing plant and leach circuits, with controllers and remote alarm indication.

Vehicle mounted detection and robotic platforms for post blast re-entry, taking measurement into an atmosphere before a person enters it.

Flame detection for fuel storage, workshops, conveyor systems and processing plant, and calibration gases to keep all of it honest.

Behind the products sit project engineering, service and calibration, field service, fleet management and hire for shutdowns and campaigns. Gastech supports mining from WA, NSW and QLD.

Our instruments are in use across gold, iron ore, copper, coal, nickel, lithium, bauxite and rare earths operations in Australia and in 94 countries.

If you are working out what your site needs, or reviewing a gas risk management chart, talk to our Technical Consultants.