Fires In Oxygen Systems

For a fire to occur, it is necessary for all three legs of the Fire Triangle to be present: Ignition Source, Fuel and Oxygen. Oxygen systems are unique because it is normally impossible to remove any of the three legs of the Fire Triangle.  Any mechanism that releases heat, such as the impact of high-speed contaminant particles, the burning of lubricants or seal materials, adiabatic compression of the gas - and many others - can be a sufficient ignition source to start a fire in an oxygen system. 

Further, in pressurised and/or concentrated oxygen, most materials - including many common engineering metals such as stainless steel or aluminium - are fuels that readily support burning.  As a result, there is typically an elevated fire risk in oxygen systems and this higher risk is recognised the world over.

When this risk is not appropriately mitigated, such as through correct selection of components and materials, a fire can occur.  Fires in oxygen systems release large amounts of energy and, since the oxygen is often subsequently vented, secondary fires commonly occur involving surrounding structures, making these component failures and ignitions especially destructive.

$100 million+ US Navy Orion Fire
This fire was thought to have started in an oxygen system manifold check valve
and then spread throughout the aircraft, destroying the airframe and all onboard systems.

Above:Aircraft fire in progress

Fire aftermath

Oxygen manifold assembly after fire