Ammonia is a colourless gas, composed of one nitrogen molecule and three hydrogen molecules. It is produced naturally in the human body, as well as in nature (water, soil, air and so on). It has a very distinct pungent odour, and might be accurately compared to the odour of cat urine. Pure ammonia (anhydrous ammonia) will exist as a gas at typical room temperatures. It will also readily dissolve in water, forming ammonium hydroxide.
For those who are not in some way associated with the refrigeration industry, a mention of the word ammonia will bring to mind a common household cleaner. That product is actually ammonium hydroxide, with the percentage of ammonia ranging somewhere between three to ten per cent. It may also include some form of detergent, along with a scent such as lemon. While it too has a pungent odour and can be irritating to the skin, it is nothing like pure NH3, the un-watered down (anhydrous ammonia) version that is commonly used as a refrigerant in industrial applications.
Each country will have its own respective regulatory agency governing owner responsibility for installation/operation/maintaining ammonia refrigeration systems. Several national and international organizations have gotten involved with providing guidance on minimizing the environmental impacts of refrigerant leaks. Other organizations have also focused on the risks associated with these leaks with regards to human safety. Through the involvement of these organizations codes and regulations have been established.
In Canada, the latter comes from various levels of government – federal, provincial as well as municipal administrations depending on the application.
Accidents that might be of minor consequence with HCFC/HFC refrigerants can result in some very serious consequences with ammonia system mishaps. Some of the more common ammonia system safety hazards are listed below:
1. Poor housekeeping practices (oily or wet floors, storing items in the machine room)
Correct it: A clean area is a safe area. Ensure your floors are clean, free of oil and water and do not use your ammonia machine room as a storage room.
2. Poor pipe quality beneath insulation
Correct it: Check for corrosion under insulation (CUI) by conducting spot checks, often performed during your mechanical integrity audit. Prevent pipe corrosion by using a corrosion inhibitor or stainless steel pipe.
3. Absence of adequate pipe labels or no maintenance program of labeling
Correct it: Follow International Institute of Ammonia Refrigeration (IIAR) Bulletin No. 114.
4. Equipment is operated outside design parameters
Materials are generally only rated for a specific temperature range. In the refrigeration industry, users may change a setpoint from -20F to -25F to try and improve production or make up for lack of capacity; however, the pipe may only be rated for -20F. Running pumps or compressors at different design conditions than intended can overload the motors.
Correct it: Operate your pumps and compressors within the designated design parameters and temperature range.
5. Failure to implement maintenance cycling program on valves. If your valves sit in one position for too long, they won’t work when you go to use them.
Correct it: “Exercise” (open and close) your valves regularly.
6. Blocked escape routes from areas with ammonia present
It may seem obvious, but do not store a big box in front of an exit. We see this mistake often.
Correct it: Ensure escape routes are clear.
7. Operators with insufficient training of ammonia refrigeration operations and safety awareness
Correct it: Ensure personnel involved with the operation and maintenance of the ammonia system receive initial training and refresher training every three years.
8. Unsafe access to frequently used valves, equipment, etc. for maintenance
Correct it: Items that require maintenance should ideally be accessible from the ground (use a chain wheel). Items up high should have a catwalk or a clear path accessible via a scissor lift or ladder.
9. Leak detection systems that are either nonexistent, inoperable, not calibrated or not tied to ventilation systems
Correct it: Perform annual testing on your leak detection systems to ensure alarms work properly.
10. Uncapped open valves
Correct it: Ensure all valves open to the atmosphere have a pipe plug or cap.
11. Open oil draining valves
Because oil draining valves have a spring return, you personnel must stand in front of them and hold them open. Some personnel might take them off and just leave them open.
Correct it: Avoid this issue by utilizing self-closing, spring-loaded valves.
12. Gas mask systems are not readily accessible
Correct it: Keep your gas mask systems close to your ammonia source.
13. Heavy ice buildup on piping and components; not taking weight into consideration
Some pipes (those below 32F) will build frost either because they are not insulated, or are not insulated properly. The ice will get thicker and thicker, creating considerable added weight. Pipe supports and the building are not designed to hold this extra weight.
Correct it: Insulate your piping and components properly.
14. Not executing safety switch testing on a consistent schedule
Correct it: Conduct annual safety switch testing.
15. Open electrical cabinets
Correct it: Close your electrical cabinets to prevent risk of shock or fire.
While an article such as this can only scratch the surface of a complex topic such as safety in an ammonia system, please see the following reference for a more comprehensive guide for safety in ammonia systems: www.epa.gov/sites/production/files/2015-05/documents/accident_prevention_ammonia_refrigeration_5-20-15.pdf.
Dave Demma holds a degree in refrigeration engineering and worked as a journeyman refrigeration technician before moving into the manufacturing sector where he regularly trains contractor and engineering groups. He can be reached at firstname.lastname@example.org.
MAIN CHARACTERISTICS OF A CLASS-T ROOM
As required by Code B52 of the CSA (Canadian Standards Association), a mechanical room with an ammonia refrigeration system must comply with Class-T requirements which include:
• A room sealed off from indoor air and constantly ventilated with outside air.
• Ventilation control outside of the room.
• Controlled access to the room.
• A door giving direct access to the exterior of the building.
• A vestibule with a fireproof door giving access to the room.
• Masks and/or personal respirators available in case of major leaks.
• Written emergency procedures.
• Staff exercises and training.
• An ammonia detector coupled with an alarm system that sets off the emergency ventilation system to exhaust accumulated ammonia vapours to the outside.
• An alarm to alert maintenance staff and firefighters.
• No combustion equipment in the room.