The old saying ‘Familiarity breeds contempt’ has dangerous implications for users of oxygen unless safety rules are rigorously applied. Oxygen is widely known to be the component of air that supports all aerobic life forms, but can represent a very grave safety hazard if handled carelessly or with negligence.

It is important to understand that oxygen behaves very differently to air, compressed air, nitrogen and other inert gases because when concentrated in its pure form it becomes far more reactive. In our familiar atmospheric environment, with an oxygen concentration of around 21%, materials such as fabric, wood, plastic, paint, oil and wax are flammable but are generally not considered to be particularly dangerous.

The reason is that the other constituents of air, making up the balance of 79%, are chemically inert under ambient conditions and therefore we are able to exist without the constant risk of fire or explosion.

Oxygen is widely transported in steel cylinders, through which it is stored under pressure of up to 300kPa in order to enable a useful quantity to be contained in the cylinder. For use, the oxygen is released from the cylinder by opening the cylinder valve that allows oxygen gas to flow safely through the pressure regulator at reduced pressure, as required by the application.

When oxygen is released at high pressure and allowed to contact certain materials, they will either explode or catch fire spontaneously. Such materials including organic compounds and many metals are said to be incompatible with oxygen.

Cylinder valves should always be opened slowly especially after a change of supply cylinder, because rapid opening can result in high oxygen velocities that will accelerate any particles in the system very rapidly and cause friction that results in a temperature rise. The pressure surge that results when a valve is opened rapidly with a regulator attached can also cause a temperature increase, because the oxygen flow is blocked by a dead-end. Fires have resulted from both these unsafe practices.

It should be recognised that even the steel cylinder neck threads and bronze cylinder valve that normally contain the oxygen pressure safely are no match for the highly reactive force exerted by a stream of pure oxygen after a cylinder fire has started. Analysis of failed cylinders indicates that the steel neck can be burned away and even the inside surface of the cylinder can reach melting temperature.

Taking unnecessary risks with high pressure oxygen cylinders is definitely not a good idea.

Oxygen enriched air
Oxygen has been widely used for industrial applications over many years and all responsible employers ensure that personnel exposed to the risk of high pressure or liquid oxygen are adequately trained and that the use of oxygen is regulated by formal procedures.

Recently, however, oxygen is more readily available in portable cylinders for healthcare applications and can also be generated at home using an oxygen concentrator.

Supplemental oxygen therapy is prescribed for the treatment of various lung, heart and blood problems, while certain individuals require oxygen when visiting high altitudes or during air travel. Extra oxygen is also beneficial during the recovery from burn injuries and after exposure to toxic substances like cyanide or carbon monoxide. A significant portion of the oxygen supplied or generated for breathing related applications is not consumed, but is released into the environment.

This can increase the average oxygen content of the air inside the room or home where supplemental breathing oxygen is used, especially in cooler climates where the air is recycled for ventilation. A dangerous situation can arise surprisingly quickly if equipment with a leaking valve or hose is used.

Even a relatively small increase in concentration to 24% oxygen can create a dangerous situation, because a fire can start far more easily and once started will burn more fiercely to produce higher temperatures than in normal air, making it impossible to extinguish. Porous and absorbent materials like clothing, rugs, curtains, upholstery and other soft furnishings are normally impregnated with air and when this is replaced with oxygen, these normally harmless materials become incredibly dangerous.

It can be lethal
The important thing to understand is that while clothing or hair can easily catch fire in the normal atmosphere, the presence of additional oxygen concentrated in the hair and clothing of the patient drastically increases this risk. Serious or even fatal burns are the likely outcome of a fire that occurs under these circumstances.

The risks associated with oxygen enrichment within a domestic environment are exaggerated by the fact that it is colourless, odourless and tasteless and therefore the presence or concentration of an oxygen enriched atmosphere cannot be easily detected by our human senses.