Oxidant enriched atmosphere, flammable atmospheres

There are no reliable theoretical equations for the combined effects of pressure, temperature, oxidant type and concentration, and fuel mixture composition on the limits of flammability. However, chemical processes are often operated at elevated temperatures and pressures and at times in oxidant enriched atmospheres. Flammability limits should be measured at actual process conditions with adequate test methods. 

Following fires in which endotracheal tubes became ignited by surgical lasers or electrocautery in atmospheres enriched by oxygen and/or nitrous oxide, the flammability of PVC, silicone rubber and red rubber tubes in enriched atmospheres was studied [1], Ozonised oxygen was reacted with hydrogen at low pressure to generate hydroxyl radicals. Pressure in the apparatus was maintained by a vacuum pump protected from ozone by a tube of heated silver foil. On two occasions there was an explosion in the plastic vent pipe from the vacuum pump. The vent gas should have been outside explosive limits and the exact cause is not clear the editor suspects peroxide formation. 

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