This is not the first time I have addressed this matter. Still, somehow, somewhere, a dirty little lie has been circulating among ammonia design and installation contractors that somehow an engine room handling less than 10,000 pounds of anhydrous ammonia (NH3) is incapable of presenting an explosion hazard, thus no need for any engineered ventilation.
This is insane logic and not anywhere near a rational risk analysis! The 10,000 pounds comes from the PSM (and RMP) threshold and has ZERO to do with potential explosion hazards from Ammonia. We could have 3,000 pounds in our system, not be covered by PSM, and yet blow up our engine/machinery room. OSHA does not even have to use their “General Duty Clause” to cite a non-ventilated engine room that is not built to a Class I, Div 2, Group D HAZLOC. And to be clear, the “exemption” that allows an ammonia refrigeration engine room from being a HAZLOC is found in NFPA 70, NOT OSHA; however, OSHA has had a long-standing position on this matter since 1990 (two years BEFORE the PSM standard!). Case in point…
This “Letter to Regional Admins” was written way back in 1990 and although I have referenced it many times, here it is:
June 13, 1990
MEMORANDUM FOR: LINDA R. ANKU
REGIONAL ADMINISTRATOR
FROM: PATRICIA K. CLARK
DIRECTOR DESIGNATE
DIRECTORATE Of COMPLIANCE PROGRAMS
SUBJECT: Dilution Ventilation and Intrinsic Safety in the Mechanical Control Room for an Anhydrous Ammonia Refrigeration System
This is in response to your memorandum of April 9, regarding the above subject. As you know, the applicable industry consensus standards for refrigeration systems, including the system that uses ammonia as a refrigerant, are contained in ANSI/ASHRAE 15-1989 (NOTE: this link is added by me – NOT OSHA and is to a 1994 edition of the standard). Section 10.14(j) of the ANSI/ASHRAE standard, however, precludes the ammonia refrigeration system control room from being classified as a Class I, Division 2 location, if the provisions contained in Sections 10.14(h) and 10.14(i) of the same standard are met.
The company at time of the inspection had not installed a ventilation system meeting the specifications of the ANSI/ASHRAE standard and, consequently, was in apparent violation of 1910.307(b), for exposing employees to explosion hazards. We advise that a 1910.307(b) citation be issued.
Because the company, [company name withheld], is proposing to install a ventilating system to meet the design requirements specified in the ANSI/ASHRAE standard, the company, will have abated 1910.307(b) violation when the system is installed. They would then not be required to install blower fans that are intrinsically safe.
It should be noted that the installation of a vapor detector system as described in your memorandum may potentially eliminate the explosion hazard but would not eliminate the inhalation hazards likely to cause death or serious physical harm.
The health hazards associated with ammonia are recognized by ANSI, as referenced in Table 2 of ANSI K61.1 – 1989 (copy attached), and a release of ammonia to contaminate the control room area in concentrations greater than 2,500 ppm in air, could be fatal if the necessary precautions are not taken. Though the referenced ANSI standard is not applicable to the situation you described, the inhalation hazard is recognized and must also be addressed by the company.
In order to protect against both safety and health hazards, the vapor detector system to be installed shall be capable of providing an audible alarm at an ammonia vapor concentration of 2,500 ppm in the air in the control room, and shall be capable of activating the exhaust blowers when the ammonia vapor concentration in the air in the control room reaches 40,000 ppm. Employees who may have to enter the control room during emergencies shall be fully equipped with the appropriate personal protective equipment, and shall be trained to meet OSHA standards at 1910.120, 1910.134, and 1910.1200.
If your staff members have any questions, they may contact Sanji Kanth at FTS 523-8031.
CLICK HERE for this Letter