Over the last several years we have come across several facilities that handle anhydrous ammonia and have a dangerous misunderstanding of “hazardous locations”. It seems that somewhere/someone had informed them that their engine room(s) did not need proper ventilation since they were below the 10,000 pound PSM/RMP threshold. They were badly misinformed and here’s why…
It is not the PSM or RMP standards that requires the engine room to have proper ventilation. It is actually the National Electric Code that requires the employer to choose one of two paths:
1) treat their engine room as a hazardous location (HAZLOC) per NEC Article 500
2) provide proper ventilation per ASHRAE 15-1994 (or more recent edition) or ANSI/CGA G2.1-1989 (or more recent edition)
Here is what NEC Article 500 Hazardous (Classified) Locations, Classes I, II, and III, Divisions 1 and 2 states…
500.5 Classifications of Locations.
(A) Classifications of Locations. Locations shall be classified depending on the properties of the flammable gas, flammable liquid-produced vapor, combustible-liquid produced vapors, combustible dusts, or fibers/flyings that may be present, and the likelihood that a flammable or combustible concentration or quantity is present. Where pyrophoric materials are the only materials used or handled, these locations shall not be classified. Each room, section, or area shall be considered individually in determining its classification.
Informational Note: Through the exercise of ingenuity in the layout of electrical installations for hazardous (classified) locations, it is frequently possible to locate much of the equipment in a reduced level of classification or in an unclassified location and, thus, to reduce the amount of special equipment required.
Rooms and areas containing ammonia refrigeration systems that are equipped with adequate mechanical ventilation may be classified as “unclassified” locations.
Informational Note: For further information regarding classification and ventilation of areas involving ammonia, see ANSI/ASHRAE 15-1994, Safety Code for Mechanical Refrigeration, and ANSI/CGA G2.1-1989, Safety Requirements for the Storage and Handling of Anhydrous Ammonia.
Again, the need to have the room rated as a Class I Div 2 HAZLOC or have the proper ventilation (i.e. ensure that ammonia will never reach 40,000 ppm as per the RAGAGEPs) is NOT driven by OSHA’s or EPA’s process safety standards, but rather the National Electric Code regarding hazardous locations. An engine room that contains much less than 10,000 pounds will still need to meet either one of the safety paths to ensure they do not develop an explosive atmosphere.