Accident Damage Protection Requirements for MC 331 Cargo Tanks

This responds to your August 18, 2005 letter requesting clarification on accident damage protection requirements for MC 331 cargo tanks under the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180).

Section 178.337-10(a) requires all valves, fittings, pressure relief devices, and other accessories to the tank proper to be protected against such damage as could be caused by collision with other vehicles or objects, jack-knifing and overturning. In addition, pressure relief vales must be protected so that in the event of overturn of the vehicle onto a hard surface, the valve will continue to function.

Section 178.337-10(b) requires protective devices or housing to be designed to withstand static loading in any direction equal to twice the weight of the tank and attachments when filled with the lading, using a safety factor or not less than four, based on the ultimate strength of the material to be used, without damage to the fittings protected, and must be made of metal at least 3/16-inch thick.

Your questions are paraphrased and answered as follows:

Q1. If there is a shear section in the valves on an MC-331 tank, is accident damage protection required per § 178.337-10(b)?

A1. Yes.

Q2. If shear sections are provided for the valving and piping, must the accident damage protection conform to § 178.337-10(b)?

A2. Yes.

Q3. If shear sections are not provided for the valving and piping, is accident damage protection required per § 178.337-10(b)?

A3. Yes.

Q4. Are the accident damage protection requirements for MC 331 cargo tanks being evaluated for consistency with the requirements for DOT-406, DOT-407, and DOT-412 cargo tanks?

A4. At this time, we are not considering modification to the accident damage protection requirements for MC 331 cargo tanks. You may petition for a rule change if you believe that modification should be considered. Procedures for submitting a petition for rulemaking are in 49 CFR 106.95.