Applicability to loading of anhydrous ammonia into cargo and portable tanks

This responds to your May 2, 2008 letter requesting clarification of requirements in the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to loading of anhydrous ammonia into cargo tanks and portable tanks. Specifically, you ask whether Note 5 to the table in § 173.315(a)(2) applies to a cargo tank filled with anhydrous ammonia or ammonia solutions to less than 87.5% by volume.

The table in § 173.315(a)(2) sets forth maximum permitted filling densities for cargo tanks and portable tanks authorized for the transportation of compressed gases. For anhydrous ammonia and anhydrous ammonia solutions with greater than 50% ammonia, the maximum permitted filling density for authorized cargo tanks and portable tanks is 82% by volume. In accordance with Note 5 to the table, uninsulated cargo tanks and portable tanks may be filled to 87.5% by volume provided the temperature of the lading (NH3) is not lower than 30º F or the filling of the tank is stopped at the first indication of frost or ice formation on the outside surface of the tank and is not resumed until such frost or ice has disappeared. Note 5 applies only to the loading of uninsulated cargo tanks filled to between 82.1% and 87.5% by volume.

According to your letter, some facilities load anhydrous ammonia at temperatures as cold as 0º F to 20º F to reduce the pressure in the trailer so that the loading process may be completed more quickly. You ask whether this practice is permitted. The answer is yes, provided all other applicable requirements are met. You also ask whether the HMR prohibit loading anhydrous ammonia at any temperature that would create frost on the tank or the associated piping. The answer is no, except as specified in Note 5 to the table in § 173.315(a)(2).

Additional guidance and information may be found in Compressed Gas Association Pamphlets G-2, Anhydrous Ammonia, and G-2.1, ANSI Requirements and Storage and Handling of Anhydrous Ammonia.