Oxygen deficiency can arise when using gases like nitrogen, carbon dioxide and argon unless good practice is observed.
This information specifies the dangers and the simple precautions to be taken to ensure that every user employs these gases with confidence and without danger.
The approximate volumetric composition of air is:
| Gas | Symbol | % | ||
| Oxygen | O2 | 21% | ||
| Nitrogen | N2 | 78% | ||
| Argon | Ar | 1% |
These atmospheric gases are non-toxic, but alterations in their concentrations - especially that of oxygen - have an effect upon life and combustion processes. It is essential to have sufficient oxygen in atmospheres being breathed.
Oxygen is not flammable itself but supports combustion whereas nitrogen and argon inhibit combustion.
If good practice is not observed accidents may happen because changes in concentration cannot be detected in good time by the human senses.
Oxygen is essential to life, and it is therefore vital to ensure that adequate oxygen is present in any atmosphere being breathed.
While a healthy person may survive a short exposure to an oxygen content as low as about 16%, no one should ever be asked to endanger their life by breathing such an atmosphere.
An insidious feature of oxygen deficiency is that it cannot readily be detected by the senses, and victims are usually unaware of the danger they are in and may even have a feeling of well-being.
Symptoms
Human beings vary considerably in their reactions to oxygen deficiency, and it is therefore not possible to lay down hard and fast rules. A general indication of what is liable to happen is given in the table below, but it should be appreciated that the reactions of some individuals may be very different from those shown, and may be increased by the presence of other gases, especially carbon dioxide.
| Oxygen content (vol %) | Effects and symptoms (at atmospheric pressure) | |
| 11-16 | Diminuation of physical and intellectual performance without the person being aware | |
| 8-11 | Possibility of fainting without prior warning | |
| 6-8 | Fainting within a few minutes, resuscitation possible if carried out immediately | |
| 0-6 | Fainting almost immediately |
Below 11% oxygen there is a risk of death due to asphyxia unless the person is resuscitated immediately.
Symptons of the possible onset of asphyxia can include:
Oxygen deficiency of the atmosphere can be caused by:
Carbon dioxide is essentially an asphyxiant gas with only mild toxic properties and no cumulative effects.
The Health and Safety Executive Guidance Note EH 40 - Occupational Exposure Limits indicates that:
The recommended exposure limit for carbon dioxide is 5,000 ppm (0.5%) by volume calculated as an eight hour time - weighted average concentration in air, or 15,000 ppm (1.5%) for a 15 minute period.
| Carbon Dioxide content (vol %) | Effects and symptoms | |
| 2-4 | Slight feeling of suffocation and an increased breathing rate | |
| 5 | Headaches, dizziness and sweating can occur after 30 min exposure | |
| 5-9 | Breathing becomes laboured, judgement is impaired | |
| 9 | Fatal on exposures of about 4 hours | |
| 12 | Immediate unconsciousness and fatality may occur after a few minutes |
It is important to note that individuals can react at different rates. Atmospheres containing less than 20% oxygen or more than 0.5% carbon dioxide should not be entered.
Apparatus used for the manufacture, distribution and utilisation of inert gases must be installed and identified in accordance with the recommendations of the industrial gas industry, and must comply with whatever regulations are applicable.
Any leak must be dealt with by people who have been adequately trained and who have the proper equipment.
Information should be provided on actions to be taken by personnel and first aiders in the event of an incident.
Operating personnel must obey works rules and regulations at all times and, where called for, protective equipment must be worn.
Before people enter a space which may be subject to oxygen enrichment or deficiency, the atmosphere should be analysed for oxygen. Free entrance is permissible only if the oxygen concentration is between 20 and 22%.
BOC Cryospeed can offer advise and supply fixed oxygen deficiency monitors and remote repeator units to help ensure you working environment is safe.
If there is any possibility of a change in concentration, anyone entering the space should wear personal oxygen monitor, which has an audible alarm when the oxygen concentration in the atmosphere varies outside the safe limits.
To make people aware of the dangers of being in an area where cryogenic liquid is located, BOC Cryospeed offer a range of warning signs which all feature UN numbers, type of cryogenic liquid and potential hazard information, including 'No Smoking' for areas with potential oxygen enrichment. All the signs are suitable for outdoor use and can easily be mounted on a wall or cage.
Please Note:
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