Below is OSHA’s official position on the need for hydrostatic relief valves in an Ammonia Refrigeration process. This is a bold move on OSHA’s part as the Ammonia Refrigeration industry and their trade groups have consistently stated that a “trained operator” is better than a hydrostatic RV.
(emphasis added by me)
Scenario: The IIAR and equipment manufacturers have historically recommended that “hydrostatic relief protection” be provided for evaporative condensers and ammonia pumps, and piping sections. However, the new American National Standards Institute (ANSI)/IIAR 2 — 1999 standard, in subsection 7.3.4, has created an exception from compliance with the hydrostatic relief requirements as follows: “b. use of trained technicians to isolate liquid-containing parts of the system.” The Refrigerating Engineers and Technicians Association (RETA) has started to teach this practice as well.
Question 10: Has OSHA taken a position with regard to the elimination of safety devices based on “trained operators”?
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 the 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 in your letter to OSHA dated October 23, 2012, ANSI/IIAR 2 – 2008 contains updated requirements to address this hazard. You requested clarification from OSHA that these updated requirements adequately address the thermal expansion hazard.
It is essential to understand that the ammonia refrigeration industry, through ASHRAE 15, ASME 31.5, and ANSI/IIAR-2, has identified liquid expansion as a hazard with potentially serious/catastrophic consequences. 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. For 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 that 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).
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)]. For situations in which liquid-filled equipment or piping could be automatically isolated as described in ANSI/IIAR 2-2008 section 11.4(b), employers could abate this hazard and address and resolve the PHA findings/recommendations by installing hydrostatic relief or expansion compensation devices as required by ANSI/IIAR 2-2008 section 11.4.2.
For liquid-filled equipment that can ONLY BE ISOLATED MANUALLY, for example, for maintenance activities, the use of trained technicians in accordance with section 11.4.1 of ANSI/IIAR 2-2008 and in compliance with the requirements of OSHA standard 29 CFR 1910.147 Control of Hazardous Energy (Lockout-Tagout) is ACCEPTABLE.
In conclusion, equipment overpressure hazards can have serious consequences, including the release of highly hazardous chemicals that could result in 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, including ANSI/IIAR 2-2008, the hazard control alternative of exclusively using trained technicians (administrative controls) to adequately control this hazard when liquid-filled equipment or piping can be automatically isolated under either normal or abnormal operating/shutdown/standby conditions or due to component fault would not be in compliance with OSHA’s 1910.119(e) standard for controlling the hazards of the process or with OSHA’s 1910.119(d)(3)(ii) standard that process equipment be documented to comply with recognized and generally accepted good engineering practices (RAGAGEP). Engineering controls, such as, but not limited to, hydrostatic relief valves or expansion compensation devices, would be appropriate safeguards for such situations. However, the use of trained technicians for the manual isolation/opening of liquid-filled equipment and piping that cannot be isolated automatically under normal or abnormal operating conditions (e.g., for maintenance) and in compliance with 29 CFR 1910.147, Control of Hazardous Energy (Lockout/Tagout) is acceptable.
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