UPDATED on 9/2/12… Is there an OSHA PSM or EPA RMP requirement that liquid ammonia piping/equipment that can trap the liquid be equipped with a proper type and sized releif device or can a “qualified refrigeration technician” take the place of a relief device? This question has been debated within the refrigeration industry PSM/RMP circles for the past 20 years; yet in 2006 OSHA answered this questions quite clearly in a LOI. In this same letter, we begin to see OSHA’s displeasure with the direction some RAGAGEP revisions are going; as they point out, the RAGAGEP may have changed, but the HAZARD HAS NOT!
Question 10: Has OSHA taken a position with regard to the elimination of safety devices based on “trained operators”?
PLEASE note the highlighted portions are done by me and NOT by OSHA
Response 10: Your scenario addresses a requirement in ANSI/IIAR 2 related to the control of an over-pressure hazard created when equipment containing liquid ammonia (NH3) is isolated. Isolated equipment has potential to be over-pressured due to thermal expansion effects of the liquid which can result in rupture and loss of containment from the equipment (liquid expansion hazard). As you mentioned, ANSI/IIAR 2 contains requirements to address this hazard. Given the serious nature of the liquid expansion hazard, you question whether the administrative control alternative listed in ANSI/IIAR 2 — 1999, Section 7.3.4 is adequate to control this hazard. You also question whether OSHA accepts administrative controls exclusively when engineering controls, i.e., safety devices, are also identified as a control measure for the same hazard/condition.
It is important to understand that the ammonia refrigeration industry, through ASHRAE 15, ASME 31.5 and ANSI/IIAR-2, has identified this liquid expansion hazard as a hazard with potentially serious/catastrophic consequences. The use of trained operators/technicians can reduce the probability that a part of a liquid-filled NH3 system might be incorrectly isolated. However, if the system relies exclusively on a trained operator to ensure safe operations, operator or procedural deficiencies (e.g., improper isolation of the equipment due to an operator error, inadequate procedure, inadequate supervision, communication error, etc.), may result in a catastrophic release because there is no other means to control/relieve the overpressure. Therefore, OSHA does not accept the use of trained technicians/operators as the sole means to control this hazard.
The 1992 edition of ANSI/IIAR 2, Section 5.4.1.4 addressed the liquid expansion hazard. Requirement 5.4.1.4 of ANSI/IIAR 2 — 1992 allowed only the use of a liquid pressure-relief device (safety system/engineering control) to control this hazard. There was no provision for utilizing a trained technician/operator (administrative control) as the sole control of the hazard. This hazard and the probability of a catastrophic release of NH3 have not significantly changed between the 1992 and 1999 editions of ANSI/IIAR 2. The two subsequent editions of ANSI/ASHRAE 15 (2001 and 2004), the Mechanical Refrigeration Safety Code, did not recognize the use of trained technicians/operators as a means to control this hazard. In fact, they specified pressure-relief devices as the exclusive means of control. Additionally, ASME Code 31.5 — 200120 — Refrigeration Piping and Heat Transfer Components, requires through Section 501.4.2 Fluid Expansion Effects (Increased Pressure) that, “Consideration must be given to expansion of liquid refrigerant trapped in or between closed valves and a means provided to prevent overpressure.”
For OSHA PSM-covered processes, including NH3 refrigeration processes, employers must conduct a process hazard analysis (PHA) to identify, evaluate and control the hazards of the process. With respect to the liquid expansion hazard, OSHA expects employers to address this hazard in all the various locations in a covered process where this hazard might exist. For this hazard, the employer’s PHA must address, among other requirements:
- The hazards of the process (e.g., the deviation or initiating event which could lead to an overpressure struck-by hazard due to flying equipment debris; toxic hazard; or fire/explosion hazard due to the release and ignition of an ignitable concentration of NH3) — 1910.119(e)(3)(i);
- The identification of any previous incident which had a likely potential for catastrophic consequences (e.g., the release of NH3 through a hydrostatic relief device due to thermal expansion of isolated liquid between equipment; a “near-miss” involving the discovery of a liquid-filled isolated NH3 line which was incorrectly identified and taken out-of-service in an area of the process where the temperature of the liquid NH3 would be expected to rise to a potentially hazardous level) — 1910.119(e)(3)(ii);
- The engineering controls and administrative controls applicable to the hazard (e.g., what controls are in-place and what safeguards exist that would likely prevent an incident from occurring following an initiating event. Such identified safeguards might include hydrostatic relief devices or piping designed to contain the effects of overpressure caused by maximum thermal expansion of the liquid) — 1910.119(e)(3)(iii);
- Consequence of failures of engineering or administrative controls (e.g., trained operators inadvertently isolate a portion of the system which has no other means to prevent overpressure of the system resulting in equipment rupture and loss of containment from the system with possible employee injuries/death; a check valve is located on the upstream side of a solenoid valve, and when the solenoid valve is de-energized, the liquid between the check valve and the solenoid is trapped, possibly leading to an overpressure condition resulting in loss of containment from the system and possible employee injuries/death.) — 1910.119(e)(3)(iv); and
- Human factors (e.g., trained operators respond to address a problem in another area of the plant, leaving an isolated liquid NH3 line in an area where significant thermal expansion of the liquid would be expected in a short time; due to a confusing piping arrangement which was not (or incorrectly) labeled, a trained technician isolates the wrong section of the process resulting in the isolation of a liquid-filled section of piping which undergoes rapid thermal expansion of the liquid and a rupture in the piping; because of a communication error with his supervisor, a trained technician incorrectly isolates a liquid-filled NH3 line in an area of the facility where thermal expansion of the NH3 would be expected.) — 1910.119(e)(3)(vi).
If a liquid expansion hazard exists and the only safeguard to protect against this hazard is the use of trained operators/technicians, then OSHA would not consider this hazard to be adequately controlled, as required by 1910.119(e). After addressing the liquid expansion hazard in the PHA, the employer must address and resolve any of the PHA team’s findings and recommendations [1910.119(e)(5)]. Employers could abate this hazard and address and resolve the PHA finding/recommendation by installing the hydrostatic relief device(s) required by ANSI/IIAR 2 — 1999, Section 7.3.4(a)
In conclusion, equipment overpressure hazards can have serious consequences including releases of highly hazardous chemicals involving multiple employee deaths. Three national consensus standards recognize and address equipment overpressure due to the liquid expansion hazard. In view of the nature of this hazard and the abatement/controls prescribed by the national consensus standards, the hazard control alternative of exclusively using trained technicians (administrative controls) to adequately control this hazard would not be in compliance with OSHA’s 1910.119(e) standard for controlling the hazards of the process.
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