US DOT Hazardous Materials Regulations (49 CFR Parts 171 to 180) 179: Tank car specifications: approval by the AAR Tank Car Committee, design, construction, pressure relief, thermal protection, head shields and the DOT 105, 111, 112, 113, 117 and 120 specifications (179.1 to 179.500)

Tank cars built or converted for hazardous materials must conform to the Part 179 specifications and be approved by the AAR Tank Car Committee before construction or alteration, with the tank car facility holding an AAR quality assurance program (179.7) and the builder certifying each car and filing the certificate of construction (179.5). Part 179 sets the general design requirements (179.10 to 179.24, including pressure relief, protective housings, thermal protection, head shields and bottom outlet protection), the pressure tank car specifications (Subpart C, DOT 105, 109, 112, 114, 120), the non-pressure specifications (Subpart D, DOT 111 and the DOT 117 and 117R specifications for flammable liquids that replaced older DOT 111 cars in flammable service under the 2015 rule), the cryogenic liquid specifications (Subpart F, DOT 113) and the mechanical and welding standards in the AAR Manual of Standards.