Abstract :
Since the very first use of optical systems in the process industries there has been a tacit assumption that, because they are not electrical, they do not present an ignition risk when used in flammable atmospheres. The author describes the results obtained from experimental work. He draws conclusions about an optical ignition mechanism and whether there is sufficient of an ignition risk for precautions to be advisable when optical systems are used in flammable atmospheres. The results obtained suggest that radiation intensities of 1×105 to 4×105 W/m2 and above are ignition capable. Modern fibre optic systems are capable of radiation intensities of 108 W/m2. The ignition mechanism requires the radiation to be absorbed by a small solid object which is thus raised to a high temperature
