Safety of optical fibre sensors in hazardous environments: ignition delay arising from stray light

Two distinct classes of experiment give evidence of the ignition behaviour of particles heated by radiation of visible and infrared wavelengths. The first type of experiment concentrates principally on small particles of reactive coal char physically attached to the ends of optical fibres, in hydrogenous atmospheres at IR wavelengths near the visible range. The second type deals with radiative ignition of various gases using CO₂ radiation and an absorber specifically chosen to be a `worst case´, combining low thermal capacity with efficient absorption of the radiation. It is suggested that the large discrepancy in ignition fluxes for different families of experiments can be reduced significantly by considering ignition delay as an important variable