By Byron Raal, CAS Founder-Editor · Last updated 8 June 2026 · About the author
Breathing air is compressed air purified to the quality limits in AS/NZS 1715:2009 Appendix A: 19.5 to 22 per cent oxygen, no more than 10 ppm carbon monoxide, 800 ppm carbon dioxide and 1 mg/m3 of oil, with no objectionable odour. Ordinary plant compressed air does not meet these limits without dedicated purification and regular testing.
Where workers breathe through airline respirators, in abrasive blasting, spray painting, confined-space entry, tank cleaning and some pharmaceutical and laboratory work, the air feeding the mask has to be controlled for oxygen, carbon monoxide, carbon dioxide, oil and moisture, and tested on a schedule with records kept. The danger is that none of those contaminants announce themselves. Carbon monoxide has no smell. Oil mist at twice the limit looks like nothing. A worker in a positive-pressure hood is the last person who can tell the air has gone bad. This page covers what compliant breathing air requires in Australia, how it is produced from a standard compressor supply, and how to verify yours, from the publisher’s text of the two governing standards rather than supplier brochures.
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What counts as breathing air, and why plant air fails
Breathing air is the supply side of supplied-air respiratory protection: air delivered by hose to a hood, helmet or full facepiece so the wearer breathes clean air instead of the contaminated atmosphere around them. Under the Australian selection tables in AS/NZS 1715, a full facepiece, head covering or air-supplied suit fed by a positive-pressure airline carries a required minimum protection factor of up to 100, which is why airline RPE is the default choice for abrasive blasting and high-exposure spray work. That protection only holds if the air going down the hose is right.
Plant compressed air is not breathing air. A lubricated rotary screw or piston compressor passes oil aerosol downstream, the intake can draw carbon monoxide from forklift traffic or engine exhaust, and an aftercooled supply still carries enough moisture to pool in low points of the line. None of that matters for a rattle gun. All of it matters inside a mask, because the respirator concentrates one person’s entire breathing intake onto whatever the line delivers, hour after hour. The general duty to manage these risks sits with the PCBU under each state’s WHS laws, and Safe Work Australia’s model Code of Practice for abrasive blasting deals with supplied-air respiratory protection in exactly this context.
The Australian framework: AS/NZS 1715 and AS/NZS 1716
Two standards divide the job. AS/NZS 1715:2009, Selection, use and maintenance of respiratory protective equipment, is the user-side standard: it covers how to select RPE for a hazard, how to run a respiratory protection program, and, in its normative Appendix A, the air quality that compressors or cylinders must deliver to supplied-air respirators. AS/NZS 1716:2012, Respiratory protective devices, is the equipment standard the respirators themselves are certified against. For air quality, AS/NZS 1716 Clause 9.16 points straight back to AS/NZS 1715, so Appendix A of 1715 is the single place the purity numbers live.
Appendix A sets these requirements for air supplied to respirators, with the gas concentrations referenced at 15 degrees Celsius and 100 kPa absolute:
| Parameter | Requirement (AS/NZS 1715:2009 Appendix A) |
|---|---|
| Oxygen | Not less than 19.5% and not more than 22% by volume |
| Carbon monoxide | Not more than 11 mg/m3 (10 ppm by volume) |
| Carbon dioxide | Not more than 1,400 mg/m3 (800 ppm by volume) |
| Oil | Not more than 1 mg/m3 |
| Odour | No objectionable or nauseous odour |
| Water (cylinder air) | Not more than 100 mg/m3, sampled from a cylinder filled to at least 12 MPa |
| Flow capacity | Minimum 170 L/min continuous flow per person, measured at the respirator |
| Supply temperature | 15 to 25 degrees Celsius recommended at the facepiece, hood or helmet |
Two scope points are worth being precise about, because suppliers routinely blur them. The numeric water limit applies to cylinder-supplied air; for compressor-supplied airline systems, Appendix A does not set a numeric water figure, but the system still has to deliver air dry enough that moisture does not condense in hoses and fittings, and the informative design guidance in the same standard calls for water traps at the low points of the distribution circuit. And the 1 mg/m3 oil ceiling is the same number as ISO 8573-1:2010 Class 3 for total oil, which is a useful translation when you are specifying a purifier package against the ISO 8573 classification system the compressed air industry actually quotes in.
The four contaminants that matter, and why you cannot sense them
Carbon monoxide is the one that kills. It binds to haemoglobin around 200 times more readily than oxygen, it has no smell or taste, and the two common sources are both outside the airline operator’s view: combustion exhaust drawn into the compressor intake (forklifts, generators, vehicles idling near the inlet), and an overheating lubricated compressor partially cracking its own oil. AS/NZS 1715’s guidance on air sources is blunt about this: locate the intake in open air, away from contamination, and treat intake filters as secondary to siting, not a substitute for it.
Oil carries over from any lubricated compressor as aerosol and vapour. Above the limit it causes headaches and nausea long before it is visible, and long-term exposure is a respiratory hazard in its own right. Moisture fogs visors, corrodes fittings, freezes regulators on cold mornings and lets microbes grow in dead legs of the line. Oxygen deficiency is rarer in compressor-fed systems but lethal where it occurs; the 19.5 per cent floor exists because an enclosed or misrouted intake can deliver air that ventilates the hood without sustaining the person in it. The common thread: a worker under positive pressure feels airflow and assumes the air is good. Flow tells you nothing about composition.
How compliant breathing air is produced
A compliant breathing-air train built off a standard plant compressor follows a consistent sequence. Each stage exists because one of the Appendix A parameters demands it:
- Intake siting. Open air, upwind and clear of exhaust sources, pressure-relief discharges and vehicle movement. This is the cheapest control in the whole train and the most commonly botched.
- Supply compressor. Either an oil-free machine or a properly maintained lubricated unit, with discharge temperature monitored, because an overheating airend is a CO generator.
- Coalescing filtration. Staged coalescing elements take out bulk water, particulate and oil aerosol ahead of the polishing stages. The same physics as plant-air compressed air filtration, specified tighter.
- Activated carbon. Adsorbs oil vapour and odour, which the coalescers cannot catch.
- Drying. To a pressure dew point that guarantees no condensation at the coldest point of the line, typically desiccant-based in packaged breathing-air purifiers.
- Catalytic CO conversion. A catalyst stage (commonly a hopcalite type) oxidises carbon monoxide to carbon dioxide. It needs dry air to work, which is why it sits after drying or a dedicated dryer stage in packaged purifiers.
- CO monitoring and alarm. A continuous monitor at the purifier outlet with an audible alarm, because the catalyst and the carbon both have finite service lives and fail silently.
- Dedicated couplings. Breathing-air outlets should use safety-type couplings that take two deliberate actions to disconnect and that are physically incompatible with plant-air fittings, so a hood cannot be plugged into shop air by mistake. Marking the service line per AS 1345 closes the same gap.
Packaged breathing-air purifiers bundle stages 3 to 7 into one cabinet with a flow rating. The specification language that matters when you buy one comes straight from the standard’s guidance: the installed system must produce air meeting Appendix A at a stated flow rate for a stated period. A purifier that meets the limits at 300 L/min for one cartridge life does not meet them at 600 L/min, and the cartridge clock is running whether or not anyone logs it.
Worked example: a two-operator blasting shed
Take a regional abrasive blasting contractor running two operators in airline hoods off the shed’s 22 kW rotary screw compressor. The breathing-air demand is fixed by the standard: 170 L/min continuous flow per person measured at the respirator, so 340 L/min (about 5.7 L/s) for the pair, before a litre goes to the blast pot. The blast nozzles themselves draw many times that from the same compressor, which is the first design trap: if the blast demand pulls line pressure down, the hoods lose flow exactly when the dust is thickest.
The compliant layout takes a dedicated tee from the receiver, ahead of the blast circuit, into a packaged purifier rated at no less than 340 L/min with coalescing, carbon and catalytic CO stages, a desiccant cartridge, and a CO monitor alarmed where the operators’ offsider can hear it. Downstream, a breathing-air manifold with two safety-coupling outlets, incompatible with the shed’s claw fittings. The intake gets moved so the diesel forklift that loads blast media cannot idle under it. Total capital for the purifier, manifold and monitor is typically a four-figure sum; the alternative being trialled informally in sheds all over the country is a hood teed straight into shop air through a single disposable filter, which fails at least three Appendix A parameters and would not survive one air-quality test.
Testing and verification
Appendix A requires regular testing of the air at the respirator, with records kept. The standard deliberately does not fix a test interval; the frequency is risk-based, and in practice Australian sites running airline RPE daily commonly test quarterly to six-monthly, with annual testing as the floor for lower-use systems. A test covers the Appendix A parameters: oxygen, carbon monoxide, carbon dioxide, oil, water and odour, sampled at the outlet the respirator actually plugs into, not at the purifier. Specialist air-quality laboratories and occupational hygienists provide this as a routine service, and a NATA-accredited test report is the document an inspector or auditor will ask for.
Between laboratory tests, the continuous CO monitor is the live safeguard, and the maintenance log on the purifier cartridges is the evidence the system is being run, not just owned. If you are specifying dew point targets for the drying stage, the dew point calculator converts between pressure and atmospheric dew point and maps the result to ISO 8573-1 water classes. For the wider regulatory picture on compressed air at work, see our guide to Safe Work Australia compressed air requirements.
Common failures we see
- Shop air in the hood. An airline respirator connected to plant air through a single particulate filter. No CO control, no oil vapour control, no testing. This is the most common and most dangerous shortcut.
- Intake in the traffic lane. A compliant purifier fed by a compressor whose intake sits beside a roller door where trucks and forklifts idle. The purifier’s catalyst handles transient CO; it is not designed to clean engine exhaust all shift.
- Interchangeable couplings. Breathing-air and plant-air outlets sharing the same claw or Nitto pattern, so the night shift plugs a hood into the wrong drop. Safety couplings and AS 1345 line marking exist precisely for this.
- Dead cartridges. Carbon and catalyst stages past their rated life or hours, with no change-out log. The air was compliant the day the purifier was commissioned; nobody can say what it is now.
- No records. Air tested once at installation, never since. Appendix A requires regular testing and records; a single dated certificate from three years ago is evidence of the gap, not of compliance.
Want your breathing-air train reviewed against AS/NZS 1715, or a compliant system specified for a new job? We connect you with independent specialists who do this for a living.
Frequently asked questions
What is breathing air under Australian standards?
Breathing air is compressed air supplied to airline respirators, hoods and helmets that meets the quality limits in AS/NZS 1715:2009 Appendix A: oxygen between 19.5 and 22 per cent by volume, carbon monoxide no more than 11 mg/m3 (10 ppm), carbon dioxide no more than 1,400 mg/m3 (800 ppm), oil no more than 1 mg/m3, and no objectionable odour, with gas concentrations referenced at 15 degrees Celsius and 100 kPa absolute. The equipment standard AS/NZS 1716:2012 points to AS/NZS 1715 for these air quality requirements.
Can I use my plant air compressor for breathing air?
Yes, but only through a dedicated breathing-air purification train and a testing regime. Raw plant air from a lubricated compressor carries oil aerosol, can carry carbon monoxide from the intake or an overheating airend, and is too wet for a mask. A compliant setup adds coalescing filtration, activated carbon, catalytic CO conversion, drying, a continuous CO monitor with alarm, and dedicated safety couplings that cannot connect to plant-air fittings, then verifies the result by regular air-quality testing at the respirator outlet.
How much breathing air does each operator need?
AS/NZS 1715:2009 Appendix A requires the air service to be sized on a minimum of 170 litres per minute of continuous flow for each person, measured at the respirator. Two airline operators therefore need at least 340 L/min (about 5.7 L/s) of purified supply before any allowance for tools or blast nozzles on the same compressor, and more where air-cooled suits or air-conditioning attachments are used.
How often does breathing air have to be tested?
AS/NZS 1715:2009 Appendix A requires regular testing of the air at the respirator with records kept, but does not fix an interval. The frequency is set by risk assessment. Australian sites using airline respirators daily commonly test quarterly to six-monthly, and annual testing is a typical floor for lower-use systems. The test should cover oxygen, carbon monoxide, carbon dioxide, oil, water and odour at the outlet the respirator connects to.
Who regulates breathing air for Australian workplaces?
Work health and safety regulators in each state and territory enforce the duty to manage respiratory risks, and Safe Work Australia publishes the model Codes of Practice that reference supplied-air respiratory protection, including the model Code of Practice for abrasive blasting. The technical requirements those duties lean on are AS/NZS 1715:2009 for selection, use, maintenance and air quality, and AS/NZS 1716:2012 for the respiratory protective devices themselves.
Related resources
- ISO 8573 air quality classes explained: the classification system purifier and filter specifications are written in.
- Safe Work Australia compressed air requirements: the wider WHS picture for compressed air at work.
- Compressed air filtration: coalescing and adsorption filtration fundamentals that breathing-air trains build on.
- Pharmaceutical compressed air: where breathing air and process air quality requirements meet GMP.
- Electronics and semiconductor compressed air: cleanroom-grade air quality specification.
- All resources: the full CAS resources library.
General information disclaimer. The information on this page is general in nature and provided for educational purposes only. It is not engineering, safety, or professional advice, and it does not account for the specifics of your site, equipment, or duty. Compressed air system design, pressure equipment selection, and regulatory compliance must be confirmed with a qualified engineer and the relevant work health and safety regulator before you act. Compressed Air Solutions is a publisher and referral service, not a licensed engineering practice, and accepts no liability for decisions made on the basis of this content. Verify all figures, standards references, and regulatory requirements against current primary sources.