30 CFR § 57.22218 Seals and stoppings (III, V-A, and V-B mines).
(a) All seals, and those stoppings that separate main intake from
main return airways, shall be of substantial construction, except that
stoppings constructed of brattice materials may be used in face areas.
(b) Exposed surfaces on the intake side of stoppings constructed of
combustible materials or foam-type blocks shall be coated with at least one
inch of construction plaster containing perlite and gypsum; at least one inch
of expanded vermiculite, Portland cement and limestone; or other coatings
with equivalent fire resistance. Stoppings constructed to phenolic foam
blocks at least 12 inches thick need not be coated for fire resistance. All
foam-type blocks used for stopping construction shall be solid.
(c) Exposed surfaces on the fresh air side of seals constructed of
combustible materials shall be coated with at least one inch of construction
plaster containing perlite and gypsum; at least one inch of expanded
vermiculite, Portland cement and limestone; or other coatings with equivalent
fire resistance. Foam-type blocks shall not be used for seals.
