Explosions in the operating theatre.

Explosions in operating theatres do not occur frequently, but unless there is constant care and watchfulness, such catastrophies can descend with tragic suddenness, and may result in loss of life or limb. Those who work in operating theatres tend to forget the dangers lurking round the corner. The writer's purpose is to bring these hazards once again to their notice, and to point out afresh some of the methods which should be adopted to prevent their occurrence. Quite recently the U.S. National Fire Protection Association Committee on Hospital Operating Rooms (I949) has published its recommendations which emphasize many easily applicable precautions which are too often overlooked. This report is full of common sense, and deals especially with the prevention of electrostatic sparks. Most of the volatile anaesthetics in common use are explosive and inflammable when their vapour is diluted with oxygen or nitrous oxide, and the mixtures thus formed will readily ignite. They are more explosive than when such vapours are mixed with air. Diethyl and divinyl ethers come into this category as does the gas cyclopropane. Trichlorethylene and chloroform when used in concentrations suitable for anaesthesia are not inflammable, nor is the unsupplemented mixture of nitrous oxide and oxygen. The vapour of ethyl chloride will burn in air with the formation of choking fumes of hydrochloric acid, but will not cause a dangerous explosion. As it is almost impossible to exclude, all the time, the accumulation of explosive mixtures of gas and vapour from operating theatres, safety must be looked for in eliminating all sources of ignition, especially electrostatic sparks. High atmospheric humidity in the theatre is not reliable in preventing such sparks. Under average conditions, explosive anaesthetic mixtures become diluted with the air of the theatre to a non-inflammable percentage before reaching a distance of two feet from a point of leak of anaesthetic vapours involving the quantities of these vapours used in ordinary surgical procedures. When ether is used however, an additional risk is present if the container breaks or spills and liquid falls to the floor to give off vapour. Because of the high rate of gas diffusion and dispersion, factors of ventilation, draughts, etc., have little effect on the'concentration of explosive gases in the limited area round the head of the patient and' the anaesthetic machine.