Probabilistic factors in radio-frequency ignition and detonation hazards analyses

Radio-frequency (RF) radiation is capable, in unfortunate circumstances, of causing undesired ignition of flammable gaseous mixtures and undesired initiation of electroexplosive devices (EEDs). All existing safety standards are based on ‘worst-case’ analyses: this implies that if an event is considered realistically possible then protective measures must be applied as if its probability were unity. Effects that are considered very improbable are effectively assigned a probability of zero. This ‘binary’ approach is unsatisfactory for a number of reasons: in particular, the concatenation of apparently realistic worst-case factors frequently leads to unacceptably ‘pessimistic’ conclusions. The solution to such problems is to evaluate the probability of occurrence of each step in the hazard process. The paper reviews the bases of the new British Standards covering these hazards and presents an analysis of some of the probabilistic factors involved.