Intrinsic safety of optical fibres in combustible environments

Contrary to widely held belief optical fibre cables are not intrinsically safe under all conditions. The results of preliminary experimental investigations into the intrinsic safety of optical fibres in combustible environments are presented. Powers in the order of 100 mW, delivered by multi-mode or single-mode optical fibres, and incident on dust particles, created explosions in combustible gas/air mixtures. Such power levels are generally higher than those used in communication systems, but are not atypical of proposed sensing systems.