Ammonia — also known as azane4 or R7172 — was among the early refrigerants, first used in 1850 in France1 in mechanical systems. A decade later, it was utilized in the United States for artificial ice production, and 10 years after that, the first ammonia refrigeration machines were patented in the 1870s. An early refrigerant, it also was one of the earliest to secure a lasting role as a refrigerant.
Ammonia is widely used in the process industries. The food and beverage industry utilizes ammonia refrigeration for their cold storage, food processing, dairy and meatpacking facilities. Ammonia refrigeration is also utilized for ice rinks, early household refrigerators, college campuses, office parks, convenience stores and larger office buildings. Ammonia refrigeration also is used at the international space station and Biosphere II — and is even being employed in power generation units.1
Ammonia — chemical formula NH3 — is a common, naturally occurring compound in the environment and one of the most abundant gases in the environment. Ammonia is environmentally friendly: it does not deplete the ozone layer or contribute to global warming, one of its three advantages over other industrial refrigerants. Other advantages include its superior thermodynamic qualities — allowing for smaller pipe sizes, smaller heat transfer areas and less electricity usage, all resulting in a 15 to 20 percent more efficient system — and its strong pungent odor. Its odor makes it easily detectible, usually detected by most individuals in the 5 to 50 ppm range, in leaks.6 Ammonia also can be detected visibly by a white vapor cloud, white smoke from burning sulfur sticks or by ammonia mounted or portable gas detectors. These detectors can be easily integrated into the DCS/SIS system.
Despite these advantages, ammonia has one disadvantage, and that is its toxicity. Due to ammonia’s hygroscopic nature, it migrates to moist areas of the body, including the eyes, nose, throat and moist skin areas, where it is both an irritant and corrosive. It may cause severe burns and eye and lung injuries. Skin and respiratory-related diseases are aggravated by exposure5 and even death is possible at higher concentrations at higher concentrations. Liquid ammonia will cause frostbite because its temperature at atmospheric pressure is -28°F.3 The Occupational Safety and Health Administration’s (OSHA) permissible exposure level (PEL) is an eight-hour time-weighted average of 50 parts per million. The National Institute of Occupational Safety and Health has established Immediately Dangerous to Life levels at 300 ppm for the purpose of respirator selection.4 Concentrations of 5000 ppm can be lethal.7
The American Industrial Hygiene Association (AIHA) has developed emergency response planning guidelines (ERPGs) for toxic substances to assist in planning for catastrophic releases to the community. The ERGP-2 represents the concentration to which individuals could be exposed to for one hour without irreversible or serious health effects and was set at 200 ppm for ammonia.4
|Ammonia can be safely used as a refrigerant provided the system is properly designed, constructed, operated and maintained.|
Although pure ammonia vapors are not flammable at concentrations of less than 16 percent, they can be a fire and explosion hazard at concentrations between 16 and 25 percent. Mixtures involving ammonia contaminated with lubricating oil from the system, however, may have a much broader explosive range. A study conducted to determine the influence of oil on the flammability limits of ammonia found that oil reduced the lower flammability limit as low as 8 percent, depending on the type and concentration of oil.4
Due to its toxicity, ammonia is classified as a highly hazardous chemical and therefore is regulated and monitored under OSHA guidelines. In 1970, OSHA issued the act that requires employers to provide a safe and healthy workplace for their employees. Then in May of 1992, OSHA passed regulation 29.CFR 1910.119 for the 14 elements of process safety management (PSM) of highly hazardous chemicals. This regulation provides the requirements to prevent or control/minimize the release of highly hazardous chemicals, whether toxic, reactive, flammable or explosive.8 This standard set the limiting quantity of 10,000 lbs, of which ammonia falls, of hazardous chemicals at a facility, unless specified differently in appendix A due to threshold quantity limits.
Additionally, in 2006 to 2009, OSHA started implementing national emphasis programs and special emphasis programs (NEPs and SEPs). The first OSHA instruction — CPL 03-00-010 — was implemented on August 18, 2009, for petroleum refinery: PSM NEP for refinery inspections. The second — CPL 03-00-014 — was implemented November 29, 2011, for PSM-covered chemical facilities. The NEP involves inspecting facilities with highly hazardous chemicals (HHCs) in amounts at or greater than the threshold quantities listed in 29.CFR 1910.119.10
Ammonia can be safely used as a refrigerant provided the system is properly designed, constructed, operated and maintained. Ammonia refrigeration facilities should be aware of the potential hazards of ammonia releases and be prepared to respond appropriately to releases should they occur. Even if the facility does not fall under PSM regulations, it is still the employer’s responsibility to provide a workplace — under the general-duty clause of OSHA and the EPA — free from recognized hazards and consistent with good recognized practice9. At minimal, if the facility is not covered under OSHA’s process safety management (PSM) standard 29.CFR 1910.119, the Chemical Accident Prevention Group of EPA’s Region III recommends the following steps that ammonia refrigeration facilities could take to prevent releases and reduce the severity of releases that do occur:
- Establish training programs to ensure that the ammonia refrigeration system is operated and maintained by knowledgeable personnel.
- Consider using a spring-loaded ball valve (dead-man valve) in conjunction with the oil drain valve on all oil out pots (used to collect oil that migrates into system components) as an emergency stop valve.
- Develop and require refrigeration maintenance personnel to follow written, standard procedures for maintaining the system, including such routine procedures as oil draining.
- Remove refrigeration oil from the refrigeration system on a regular basis. Provide barriers to protect refrigeration equipment, i.e., lines, valves and refrigeration coils, from impact in areas where forklifts are used.
- Develop and maintain a written preventive maintenance program and schedule based on the manufacturers’ recommendations for all of the refrigeration equipment.
- Perform regular vibration testing on compressors. Document and analyze results for trends.
- Maintain a leak-free ammonia refrigeration system. Investigate all reports of an ammonia odor and repair all leaks immediately. Leak test all piping, valves, seals, flanges, etc., at least four times a year.
- Consider installing ammonia detectors in areas where a substantial leak could occur or if the facility is not manned 24 hours/day.
- Replace pressure-relief valves (PRVs) on a regular schedule (consult ANSI/IIAR Standard 2– Equipment, Design, and Installation of Ammonia Mechanical Refrigerating Systems).
- Replace single PRVs with dual relief valve installations.
- For large systems with many PRVs, consider using the arrangement shown in figure 1 for detecting leakage. This arrangement includes installation of a rupture disc upstream of each PRV with a gauge port or transducer in between the disc and PRV, and installation of an ammonia sensor in the PRV common manifold.
- Ensure that the ammonia refrigeration system is routinely monitored.
- Keep an accurate record of the amount of ammonia that is purchased for the initial charge to the refrigeration system(s) and the amount that is replaced. Consider keeping a record of the amount of lubricating oil added to the system and removed from the system.
- Ensure that good housekeeping procedures are followed in the compressor/recycle rooms.
- Properly post ammonia placards (i.e., NFPA 704 NH3 diamond) and warning signs in areas where ammonia is being used as a refrigerant or being stored (for example, compressor room doors). This requirement is not the same as the in-house color coding system.
- Periodically inspect all ammonia refrigeration piping for failed insulation/vapor barrier, rust and corrosion.
- Carry out regular inspections of emergency equipment and keep respirators, including air-purifying and self-contained breathing apparatus (SCBA) and other equipment, in good shape.
- Consider using the compressor room ammonia detector to control the ventilation fans.
- Identify the king valve and other emergency isolation valves with a large placard so that they can easily be identified by emergency responders in case of an emergency.
- Establish emergency shutdown procedures and instructions on what to do during and after a power failure.
- Consider installing a solenoid valve in the king valve line operated by a switch located outside of the compressor/recycle room.
- Establish written emergency procedures and instructions on what to do in the event of an ammonia release.
- Regularly conduct emergency response drills.
- Stage a realistic response spill exercise with the local fire department.
- Mount a compressor room manual switch outside of the compressor room and identify it with a placard for use in an emergency. Mount windsocks in appropriate places and incorporate their use into the facility emergency response plan.
- Keep piping and instrumentation diagrams (P&IDs), process flow diagrams, ladder diagrams, or single lines up-to-date and incorporate them into training programs for operators.
Along with the above recommendations, the OSHA Global Alliance recommends the following checklist, although not are all inclusive of all documentation required for PSM, for ammonia facilities.1 Your recordkeeping should include the:
- Last two compliance audits.
- Last two process hazard analyses (PHAs) with closure documentation.
- Documentation of PHA communication with employees.
- Action item list for all compliance audit and PHA findings/recommendations.
- Written maintenance procedures for all ammonia refrigeration equipment.
- Piping and equipment inspection documentation.
- Documentation of ammonia detector testing and calibration.
- Current written operating procedures for the ammonia refrigeration process.
- Active hot work program with completed forms.
- Current and active P&ID.
- Pipe labeling and valve tagging consistent with P&ID.
- Completed and active management-of-change forms.
- Completed and active pre-startup safety review (PSSR) forms.
- Contractor ammonia-related injury and illness log.
With all of ammonia’s environmental and energy efficient advantages, its toxicity is still a great concern. But with proper installation, maintenance, programs and documentation intact, ammonia is a great choice as a refrigerant for cooling and freezing needs. It will be interesting to see how ammonia’s use as a refrigerant is utilized over the next few years since currently only approximately 2 percent of the ammonia produced is used for refrigeration purposes.
1.http://www.aboutammoniarefrigeration.com/aaranswers_history.cfm. International Institute of Ammonia Refrigeration (IIAR)
2. RM Technologies Inc. http://www.rmtech.net/Refrigeration.htm. Copyright © .
3. http://en.wikipedia.org/wiki/Ammonia. Last updated Dec 1, 2013 19:58.
4. Hazards of Ammonia Releases at Ammonia Refrigeration Facilities (Update). United States Environmental Protection Agency. EPA 550-F-01-009. August 2001.
5. Storage and handling of Ammonium Hydroxide. Tanner Industries, Inc. 735 Davisville Road, Third Floor, Southhampton, PA 18966. Document Verification Assessment 1995 – File TC NC2068
6. Danfoss Global Group. http://www.danfoss.com/BusinessAreas/RefrigerationAndAirConditioning/Refrigerants/WhyAmmonia.htm
7. Tenenbaum, David. The Air conditioning Refrigeration Toolbox Manual. An ARCO book. ©1990 by David Tenenbaum.
8. https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9760. Department of Labor, OSHA website.
9. A Manager’s Guide to PSM Process Safety Management. The Industrial Refrigeration Consortium. Douglas T Reindl, Director. www.irc.wisc.edu. ©2006.
10. https://www.osha.gov/dep/neps/nep-programs.html. Department of Labor, OSHA Website.
11. http://www.gcca.org/wp-content/uploads/2013/04/PSM-NEP_documentation_checklist.pdf. OSHA and the Global Cold Chain Alliance, March 2013.