Dip tanks exceeding 20-gallon capacity shall not be used or maintained on any combustible floor. Dip tanks of 20-gallon capacity or less shall not be used or maintained on combustible flooring unless the floor under such tanks, and for a distance of 5 feet on all sides of dip tanks, drain boards, and objects which have been dipped is protected with a covering of noncombustible material in such a manner as to prevent the floor from becoming saturated or covered with flammable or combustible liquids used in the dipping process.