Oxygen enrichment can arise when using oxygen unless good practice is observed. This information specifies the dangers and the simple precautions to be taken to ensure that every user can employ oxygen with confidence and without danger.
The approximate volumetric composition of air is:
The approximate volumetric composition of air is:
| Gas | Symbol | % | ||
| Oxygen | O2 | 21% | ||
| Nitrogen | N2 | 78% | ||
| Argon | Ar | 1% |
The 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.
Although not itself flammable, oxygen does support 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 reacts with most elements. The initiation, speed, vigour and extent of these reactions depend in particular upon:
Before people enter a space which may be subject to oxygen enrichment, the atmosphere should be analysed for oxygen. Free entrance is permissible only if the oxygen concentration is between 20 and 22%. However, if there is any possibility of a change in concentration, anyone entering such a space shall be issued with a personal continuous oxygen measuring device giving an audible alarm when the oxygen concentration in the atmosphere varies outside the safe limits.
Combustibility of materials
Oxygen enrichment of the atmosphere, even by a few percent, considerably increases the risk of fire. Sparks which would normally be regarded as harmless can cause fires and materials which do not burn in air, including fireproofing materials, may burn vigorously or even spontaneously in enriched air.
Hydrocarbon oil and grease
Oil and grease are particularly hazardous in the presence of oxygen as they can ignite spontaneously and burn with explosive violence. They should never be used to lubricate oxygen or enriched air equipment (special lubricants which are compatible with oxygen can be used under certain conditions).
Smoking
Many burning accidents which occur are triggered off by the lighting of a cigarette, therefore it is impossible to over-emphasise the danger of smoking in oxygen enriched atmospheres or where oxygen enrichment can occur. In such areas smoking must be forbidden.
Oxygen enrichment of the atmosphere can be caused by:
Apparatus used for the manufacture, distribution and utilisation of oxygen 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, first aid and firefighting teams in the event of an incident.
Operating personnel must at all times obey works rules and regulations and, where called for, protective equipment must be worn.
Many so-called non-flammable textiles will burn fiercely in air containing as little as 30% oxygen, and no material should be considered safe unless it is known to have been subjected to a proper test.
Some synthetic materials including polyamides may be fire- resistant to some extent, but they can cause serious burns due to the adhesion of molten material.
Fire-proofing with borax can be useful, but washing reduces the effectiveness of the treatment.
Clothing should be well fitting, yet easy to remove and free from oil and grease. People who have been exposed to an oxygen enriched atmosphere must not smoke or go near hot spots or sparks until they have properly ventilated their clothes in a normal atmosphere. A ventilation period of 5 minutes minimum, with movement of the arms and legs and with coats unbuttoned, is necessary.
Under oxygen rich conditions, the best fire fighting media are water or extinguishers containing dry chemical powder or carbon dioxide. Fire fighting equipment should be properly maintained and workers should know where it is located and how to operate it.
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 enrichment 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.