Fibers and flyings that accumulate on surfaces, especially heated surfaces, may become carbonized or excessively dry and this may make them more easily ignited, and thus more hazardous. This is one reason one reason
Even without blanketing effects, surface temperatures must not ignite fibers or flyings that may make contact with those surfaces. why surface temperatures surface temperatures
From NEC 503.5:
" Equipment installed in Class III locations shall be able to function at full rating without developing surface temperatures high enough to cause excessive dehydration or gradual carbonization of accumulated fibers/flyings. Organic material that is carbonized or excessively dry is highly susceptible to spontaneous ignition." of electrical equipment must be carefully controlled.

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