You must NEVER smoke, carry a lighted cigarette or perform any activity involving fire within 25 feet of __________.

Do not smoke within 25 feet of a placarded cargo tank used for Class 3 (flammable liquids) or Division 2.1 (gases). Also, do not smoke or carry a lighted cigarette, cigar, or pipe within 25 feet of any vehicle, which contains:
Class 1 (Explosives).
Class 3 (Flammable Liquids).
Class 4.1 (Flammable Solids).
Class 4.2 (Spontaneously Combustible).
Class 5 (Oxidizers). [Commercial Driver Handbook]