(a) Fan houses, fan bulkheads for main and booster fans, and air
ducts connecting main fans to underground openings shall be constructed of
noncombustible materials.
(b) Areas within 25 feet of main fans or booster fans shall be free
of combustible materials, except installed wiring, ground and track support,
headframes, and direct-fired heaters. Other timber shall be coated with one
inch of shotcrete, one-half inch of gunite, or other noncombustible
materials.
