The DOT and PHMSA has jurisdiction for the loading, storage (incidental to transportation), transporting and loading / unloading of NH3. Both the DOT and the PHMSA are silent on the specific requirements for the material used in the manufacturing of the delivery hose for ammonia.
In general when a hazard is not specifically addressed in the DOT regulation, Section 4(B)(1) of the OSHA act would apply. A review of the OSHA 29 CFR 1910.111(B)(8) regulations indicates that the hose used in ammonia transfer operations must conform to the joint standard defined by The Fertilizer Institute – Rubber Manufacturers Association (TFI-RMA) standard No. M-5.
After close examination of the TFI-RMA M-5, Appendix B specifications for Anhydrous Ammonia, metal hose assemblies fail the standard for the following 2 specifications:
7.4.2 Conditioned Hose Flexing Test: 220.127.116.11 As stated in the TFI-RMA M-5 specification “The flexing test shall continue for 72 hours at a rate of approximately 470 cycles per hour with a 42 inch vertical movement of a traveling block (72 X 470 =33,840 cycles)” Corrugated metal hose is made to the NAHAD 400 guidelines and must meet a 10,000 flexing cycle which is 1/3 of the cycles needed to meet the TFI-RMA M-5 specification.
10.0 Markings: As stated in the TFI-RMA specification, “Anhydrous Ammonia Hose assemblies shall be clearly marked at least once every five feet with manufacture’s name or trademark, Anhydrous Ammonia, the maximum working pressure in psig, year of manufacture, and TFI-RMA spec” for all hose manufactured after January 1, 1964. Note metal hose assemblies have no markings on the hose.
Additional practical constraints should also be considered, such as the life span of metal vs. rubber in harsh conditions, and the inability for the operator to completely empty a metal hose of product between deliveries. This latter concern is not a problem for facility hoses that are stored “wet”, but would be a sever hazard for the transport operator who must handle and work with a hose containing residual product.