What is the potential risk?

Common health hazards of anhydrous ammonia arise from its inhalation and corrosive effects. These effects can harm workers if there is an accidental release. In addition to the health hazard, at higher concentrations — for example, during a significant release in an enclosed area — and with ineffective controls, a fire or explosion may occur.

Ammonia is a flammable and colourless gas with a strong odour. Applications of ammonia include:

• Refrigeration systems
• Fertilizers
• Combustion emission control
• Other industrial processes

It has a lower explosive limit (LEL) concentration of 15 percent, which means this concentration of ammonia in conjunction with oxygen and an ignition source can result in a fire or explosion.

Through inadvertent leaks in the system, oil mixed with the ammonia refrigerant further increases the risk of fire or explosion by expanding the flammability range of ammonia, including reducing the concentration of ammonia necessary for a fire or explosion. Due to the presence of oil, even low-flammable, synthetic refrigerants have the potential for fire or explosions.

Which industries may be at risk?

Workplaces that use ammonia as a refrigerant or for other industrial processes may be at risk of fire or explosion. These workplaces may include the following:

• Ice rinks and curling rinks
• Food and beverage product manufacturing and wholesale
• Cold storage facilities
• Supermarkets
• Ice manufacturers

How can I reduce the risk in my workplace?

As an employer, you need to know if there is the potential for the risk identified in this advisory to be present in your workplace. It’s your responsibility to regularly inspect your workplace, and to ensure that your safety procedures and practices control the risk.

The following controls can prevent a fire or explosion from occurring:

• Preventative maintenance and ensuring mechanical integrity of piping and equipment is sustained throughout their life cycle
• Continuous monitors connected to a central alarm system in areas where loss of containment of ammonia could happen
• Continuous and emergency ventilation of machine room enclosure with air flow meeting the current CSA B52-13 Mechanical Refrigeration Code standard
• Emergency shutoff or shutdown of system that can be accessed remotely (i.e., outside of machine room enclosure)
• Control of ignition sources

Other ways to reduce the risk include the following:

• Develop and implement emergency procedures for evacuation and response.
• Conduct drills to test the adequacy of procedures. Make sure that workers and supervisors are familiar with their roles and responsibilities.
• Ensure that muster points are far enough from the building to protect workers from a fire or explosion.
• Ensure that emergency procedures are designed to protect all workers, including evacuees and responders. This should take into account the detection ranges of monitoring devices relied upon during an emergency.
• Implement mitigation controls in case of loss of containment outside of machine room enclosure. This may include remotely operated valves and adequate dilution ventilation.
• Verify that safety-critical prevention and mitigation controls are working properly. For each of those controls, identify what verifications to do and how often to do those verifications.
• Implement a system to notify responders of emergency conditions when the site is unattended. Notifications will provide a safer, more rapid response before the emergency worsens.
• Develop and implement safe work procedures for isolation, lockout, and purging of ammonia system.
• Maintain up-to-date diagrams of the refrigeration system piping and equipment. This should include available valves to allow isolation, lockout, and purging.
• Equip workers in the vicinity of ammonia system with the appropriate personal protective equipment.
• Monitor the amount of oil added or drained from the system to lessen the risk of fire or explosion.

Where can I find more information?

• Anhydrous ammonia safety for industrial refrigeration systems: Guide to risk identification and controls for employers
• OHS Regulation
  • Section 5.27: Ignition sources
  • Section 5.31: Flammable gas or vapour
  • Sections 5.91–5.102: Emergency procedures
  • Sections 6.116–6.132: Toxic process gases
• OHS Guidelines
  • G6.116-1–G6.127: Toxic process gases
• CSA B52-13 Mechanical Refrigeration Code (Enclosures, Ignition Sources, Ventilation)

Learn more about managing risk.