What Are the Key Measurements to Ensure Safety in Breathing Air?

Breathing air applications are not just restricted to checking the quality of compressed gas in breathing sets and systems fitted for patients in hospitals but also the breathable levels of oxygen in compartments that might hold inerting gas generation equipment or electrolysers. These are often unmanned, and a remote monitoring system is required to allow safe entry.

Some ships and refinery plants have fire suppression systems using gases like Inergen, Argonite and FM 200. These remove oxygen from the atmosphere. If they are used, then the compartment or enclosed space in which they are used needs to be checked that Oxygen levels are safe for entry.

What measurements are essential for breathing air?

About 78% of the air we breathe is nitrogen, an average of 20.9% (at sea level) is oxygen. The balance consists of argon and then trace amounts of CO, CO2, water vapour and noble gases such as neon and helium.

Instruments to monitor breathing air and breathable atmospheres form a core of products available from Process Sensing Technologies (PST). PST instruments and sensors can be used to check moisture content, and oxygen content as well as N2, CO and CO2 levels.

Humidity and moisture measurements

A certain level of humidity is necessary for breathing air. If the air is too dry, it will dry out the user’s breathing passages which will be uncomfortable at the very least and may also be dangerous over long periods or in certain situations. On the other hand, too much moisture in the breathing apparatus may damage valves or encourage bacterial growth.

Portable hygrometers are ideal for making spot-checks of breathing sets, bottles and fixed gas lines. It’s important to select one that is capable of measuring moisture in gas at line pressure.

Online hygrometers are suitable for providing continuous measurements of compressors at the point of delivery.

Oxygen, CO and CO2 measurements

Hand-held O2and CO monitors are a convent way to check oxygen levels in tanks of breathing air, as well as check for dangerous levels of carbon monoxide (CO). Monitoring for CO is especially important since CO poisoning is very often fatal.

Ambient O2 monitors ensure safety in confined spaces where there is a risk of gas leaks. They sound alarms if O2 levels drop below safe levels.

Measuring O2 levels in gas generation systems confirms the purity of oxygen produced. These analyzers may also include CO, CO2 and moisture sensors to provide a full picture of the breathing gas quality.

Diving gas mixtures

Technical and commercial divers breathe a special gas mixture of nitrogen, helium and oxygen. The ratios of these gases vary depending on the depth of the dive and a specialist Trimix or Heliox Analyzer is recommended.

What is a breathable atmosphere?

A breathable atmosphere is one where oxygen is kept between 19.5 to 23.5%: this is the OSHA (Occupational Safety and Health Administration )1910.146 regulation.

If O2 levels drop below 19.5 and down to 16% the cells in the body do not get the oxygen needed for their correct function. Below 14% down to 10% physical activity becomes exhausting and below 6% fatalities will happen. Loss of consciousness can occur quickly: within 40 seconds.

Altitude also affects oxygen levels. As altitude increases, atmospheric pressure drops and the air thins out. Because of this, the composition of the air also changes, with a gradual reduction of the normal gases (Oxygen, Nitrogen and Argon) and an increase in Hydrogen and Helium.

For example, you can expect oxygen levels of 20.9% at sea level but at 2000m it is just over 16% O2, and by the time you reach 7,500 m you are down to 8%. This means that with each breath you receive less oxygen which can lead to hypoxia, also called ‘altitude sickness’ - which can be fatal.

Breathing air sets: Self-Contained Breathing Apparatus, SCBA

These are used by the emergency services and generally consist of one or two bottles filled with a clean compressed air to a pressure of 200-300 bar connected to a sealed mask, or a mouthpiece with a demand valve that drops the pressure of the compressed air to a breathable level.

Breathing air standards do vary but not by much, for example:

Europe BS EN12021:2014 US CGA G-7.1.2011 Grade D Australia & New Zealand AS-NZS 1715:2009
Oxygen 21 +/- 1% 19.5-23.5% 19.5-22%
Carbon Dioxide ≤ 500 ppm ≤ 1000 ppm ≤ 800 ppm
Carbon monoxide ≤ 5 ppm ≤ 10 ppm ≤ 10 ppm
Oil ≤ 0.5 mg/m3 ≤ 0.5 mg/m3 ≤ 1 mg/m3
Water airline <40 bar Storage 5°C below lowest storage temperature: where storage and usage temperatures is not known pressure dewpoint will not exceed -11°C Dewpoint≤ 50°F (67 ppmV, for SCBA use in extreme cold dew point not to exceed -65°F (24 ppmV) or 10°F lower than the coldest temperature is worn in.
Water high pressure 40 to 200 bar ≤ 35 mg/m3
  • 200 bar ≤ 35 mg/m3
  • HP charging compressor ≤ 25 mg/m3
  • ≥100 mg/m3 for cylinders initial filled to pressure of at least 120 B

    What instruments are recommended for breathing set testing?

    Michell MDM300 high-speed portable hygrometer. This is also available with a tough Peli case, and is capable of measuring moisture at line pressure.

    SF82 Online Hygrometer for charging compressors for delivery.

    Analytical Industries AII-3000 and Palm O2 handheld monitors measure oxygen levels in tanks of breathing air. The Palm CO ensures that CO levels are not dangerous.

    Instruments to ensure safety of divers’ breathing air

    Diving should be considered a separate breathing air application. Divers’ air should also conform to BS EN12021.

    Further, it is divided into two categories, depending on the diving depth the swimmer must get to or work at.

    Sport divers and shallow water divers can work on standard 21% O2 with a balance of N2 to a depth of 30m.

    Technical and commercial divers reach depths below 30m. At these depths, high N2 levels can cause nitrogen narcosis. This has the effect of causing a drunken-like effect and can be fatal.

    Also, by reducing the amount of nitrogen in a diving set and substituting it with helium the effects of and decompression times to reduce the bends can be reduced. The bends, decompression sickness or Caisson disease, can occur both in divers and for people at high altitude. Nitrogen can come out of solution as bubbles in the blood and can affect the whole body including joints, heart, lungs and brain. The term ‘bends’ came from the cramped-up body shape divers suffering from it took to try and relieve the pain.

    Advanced sport divers and professional divers (such as those in various Navies tasked with bomb and mine recovery and disposal as well as commercial divers working on oil & gas platforms) will use either a trimix gas or heliox in their diving sets.

    Below 65m even oxygen can become toxic to the central nervous system as the partial pressure of oxygen rises at depth. So extra helium is used to reduce the amount of oxygen, a typical trimix could be 15% O2, 55% he, and 30% N2.

    PST equipment for diving air set testing:

    Michell MDM300 high-speed portable hygrometer.This is also available with a tough Peli case, and is capable of measuring moisture at line pressure.

    SF82 Online Hygrometer for continuous measurements of moisture at the compressor.

    Analytical Industries AII-3000 and Palm O2 handheld monitors

    Analytical Industries AII Trimix 4001 automatically calculates and measures the correct mix of helium, oxygen and nitrogen for technical divers.

    Decompression & Hyperbaric chambers

    The decompression chamber is used by deep commercial divers in order to compress and decompress them in a safe manner. It is surface-supplied and is essentially a living space with an airlock for transfer of food etc. It can also be connected to a diving bell. Divers can spend several days in one as they are compressed and decompressed.

    The hyperbaric chamber is used in medical treatment and it can also be used to treat altitude sickness by placing a victim in an oxygen-rich atmosphere to aid their recovery. This can be for post injury operations and circulatory diseases where an increased level of oxygen at pressure is beneficial.

    PST equipment for decompression and hyperbaric chambers:

    Michell MDM300 high-speed portable hygrometer. This is also available with a tough Peli case, and is capable of measuring moisture at line pressure.

    SF82 Online Hygrometer for continuous measurements of moisture at the compressor.

    Analytical Industries AII Trimix 4001 automatically calculates and measures the correct mix of helium, oxygen and nitrogen for technical divers.

    Hospital gases

    Hospitals use a wide variety of gases, the main ones are:

  • Oxygen (O2): Mainly used with anaesthetic and ventilator equipment
  • Nitrous oxide (N2O): Used in operating theatres with O2 and other anaesthetic agents
  • Medical air 400 KPa or 4 bar (MA 4): Used for respiratory applications
  • Medical air 700 KPa or 7 bar (MA 7): Often called instrument, air it is used to drive medical tools
  • Carbon dioxide (CO2): Used in open heart and laparoscopy procedures
  • Nitrogen (N2): Sometimes used to drive medical tools
  • These gases can either be distributed by a network of pipelines or, in cases like the CO2, be delivered direct from a bottle. Many hospitals have gas production and storage areas.

    Medical Air & Gas - Compressed Air Testing - Trace Analytics (airchecklab.com)

    The gases used for breathing again must conform to BS EN 12021

    PST equipment for hospital gases:

    Michell MDM300 high-speed portable hygrometer. This is also available with a tough Peli case, and is capable of measuring moisture at line pressure.

    SF82 Online Hygrometer for continuous measurements of moisture at the compressor.

    Analytical Industries AII Trimix 4001 automatically calculates and measures the correct mix of helium, oxygen and nitrogen for technical divers.

    Ntron MoGas Medical Gas Analyzeris designed to confirm the purity of oxygen generated for medical use.

    Confined spaces and rooms

    The HSE definition is: A confined space is a place which is substantially enclosed (though not always entirely), and where serious injury can occur from hazardous substances or conditions within the space or nearby (e.g. lack of oxygen).

    These could be N2 generation areas for inerting gases, or electrolyser facilities where both H2 & O2 are being produced.

    There can also be hypoxic areas. These are areas with low oxygen levels either for fire prevention (libraries storage for example) or to prevent oxidation of food stuffs, or paints and chemicals.

    Monitoring equipment such as the Ntron Gasenz and Ntron OxyTx for hazardous areas can give warning of low O2 levels. These would be permanently mounted in the spaces. Their displays can be placed in normal habitable areas or their outputs sent to warning systems in control rooms.

    CO and CO2 are both gases which need to be monitored in confined areas, or rooms with low ventilation areas.

    Carbon Dioxide levels in confined spaces

    As a guideline the following levels apply to CO2 which occurs at 0.03% in normally breathable air:

    250-350 ppm: Normal, outside air-breathing level. Low risk

    350 - 1,000 ppm Normal, indoor air-breathing level. Low risk

    1,000 - 2000 ppm: Elevated levels in poor quality air, higher risk of drowsiness

    2,000-5,000 ppm: High Levels in poor quality air: dizziness, nausea, increased heart rate will occur

    >5,000 ppm UK Long Term Exposure Limit (8 Hour Reference Period)

    >15,000 ppm: UK Short Term Exposure Limit

    Carbon Monoxide levels in confined spaces

    The following applies to CO which is a lethal gas (source Wikipedia):

    Effects of carbon monoxide in relation to the concentration in parts per million in the air:

    Concentration Symptoms
    35 ppm (0.0035%) Headache and dizziness within six to eight hours of constant exposure
    100 ppm (0.01%) Slight headache in two to three hours
    200 ppm (0.02%) Slight headache within two to three hours; loss of judgment
    400 ppm (0.04%) Frontal headache within one to two hours
    800 ppm (0.08%) Dizziness, nausea, and convulsions within 45 min; insensible within 2 hours
    1,600 ppm (0.16%) Headache, increased heart rate, dizziness, and nausea within 20 min; death in less than 2 hours
    3,200 ppm (0.32%) Headache, dizziness and nausea in five to ten minutes. Death within 30 minutes.
    6,400 ppm (0.64%) Headache and dizziness in one to two minutes. Convulsions, respiratory arrest, and death in less than 20 minutes.
    12,800 ppm (1.28%) Unconsciousness after 2–3 breaths. Death in less than three minutes.

    We offer the following options for monitoring carbon dioxide and carbon monoxide levels in confined spaces:

    The Rotronic Monitoring System is a complete cloud-based monitoring system that can be used to monitor CO2 levels in confined spaces or areas with limited ventilation.

    Rotronic offers a dedicated CO2 display, which also displays temperature and humidity, for complete indoor air quality monitoring.

    Ntron Microx 406, Carbon Dioxide Analyzer and the Ntron Microx 401, Carbon Monoxide Analyzer are cost-effective units that provide reliable and fast responses to changes in air composition. Contact us to find out more about these options.

    Have a question? Get in touch!

    Our team of application specialists will be happy to discuss your specific breathing gas application. Use this form to contact us.




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    Related Products

    Compressed Gas Dew Point Meter - Easidew PDP
    Dryer Portable
    Fast-Response Dew-Point Hygrometer - Michell SF82 Online
    Medical Gas Analyzer - Ntron MoGas
    Ambient Oxygen Analyzer - Ntron Gasenz
    Portable Diving Mix Analyzer - AII Trimix 4001


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