Section 41(4) in West Bengal Municipal (Building) Rules, 2007
(4)The following materials shall, for the purpose of sub-rule (2), be deemed to be fire-resisting, but not incombustible :(a)sal, teak, and other hard timber, when used for beams or posts or in combination with steel, the timber and the steel (if any) being protected by plastering in cement or other incombustible or non-conducting external coating;(b)in the case of staircases, sal, teak or other hard timber, not less than four centimetres thick; and(c)in the case of staircases, sal, teak or other hard timber, the treads and risers being not less than four centimetres thick.
