Industrial refrigeration systems - Anhydrous ammonia alarm setting concerns

What is ahydrous ammonia?

Anhydrous Ammonia (without water) is colourless gas in compressed liquefied form (UN 1005 AMMONIA, ANHYDROUS). It is most commonly used in refrigeration systems for cold food storage, dairy products manufacturing, ice rinks and beverage manufacturing. Anhydrous Ammonia can cause severe irritation to eyes, skin and respiratory tract, and destroys delicate respiratory tissue in the lungs, causing pulmonary and respiratory distress. A 30 minute exposure at a level of 1700ppm (part per million) could result in fatality.

What alarm settings should occupiers be using?

Alarm settings will depend on the specific circumstances of the site, however in determining an acceptable alarm setting the occupier should:

Important: Sites that have alarm settings higher than 300ppm are placing a significant risk to the safety to people and property.

1. Consider international exposure levels and guidelines:
   • USA EPA Acute Exposure Guideline Levels (AEGL), has an AEGL-2 level of 160ppm for 1 hour and 110ppm for 4 hours, where a person could experience serious or irreversible effects
   • US National Institute of Occupational Safety and Health (NIOSH) has an Immediately Dangerous to Life and Health (IDLH) value for ammonia gas of 300ppm
2. Complete a comprehensive risk assessment – with consideration to the following:
   • storage volume of Anhydrous Ammonia
   • site layout and occupied buildings
   • surrounding neighbours and location of sensitive areas

What about evacuation alarm settings?

Evacuation alarm settings should be lower than the IDLH concentration of 300ppm because the concentration of ammonia will be higher at the leak point than at the location of the fixed gas monitors.

Emergency Response Plan (ERP)

As with all dangerous goods, an effective ERP should document the specific incident staged response actions required when dealing with an incident/leak. The ERP must include actions that reflect the severity of the incident release - from leak investigation, relevant PPE, containment protocols, and full site evacuation protocols. The ERP should also trigger an action to monitor all occupied site areas until the area is declared safe, as well as notifying neighbouring sites and the Emergency Services.

It is imperative that when questioned, that the occupier is able to provide a justification for their response actions and evacuation protocols.

Important: Sites housing large volumes of Anhydrous Ammonia in densely populated areas, should also undertake consequence modelling for a major leak scenario. The modelling should determine where the resulting gas cloud could travel and if it can reach protected and public places, and demonstrate the resulting risk to workers and neighbours is within acceptable risk limits.

Gas detectors

Detectors should be positioned in areas where the risk of leaks have been determined. Fixed detectors should also be positioned inside the plant room and in roof spaces (where applicable). Detectors with audible and visual alarms should warn persons of a leak before entering a plant room. In addition, hand held detectors should be used by technicians when investigating leaks to ensure the actual concentration is established and monitored.

Ventilation

The emergency ventilation system must be an independent ventilation system that meets the requirements of AS/NZS 5149.3:2016 Refrigerating systems and heat pumps - Safety and environmental requirements Installation - clause 6.3.3 Mechanical Ventilation.

Note: the ventilation control panel must be located outside the plant room.

Discharge provisions

When discharging Anhydrous Ammonia, it must be into areas away from public and protected places and positioned well away from air intake of buildings. Although lighter than air, when released, the cold gas will tend to initially behave as a dense gas and then gradually rise as it warms. As such the height of the vent line for the effective dispersion of Anhydrous Ammonia into atmosphere should be calculated taking into consideration the refrigerant charge of the system*.

*Refrigerant charge is a term used for the type and mass of refrigerant a refrigeration plant will hold under the given conditions. The American Conference of Governmental Industrial Hygienists Conference (ACGIH) has a manual that provides calculations - Industrial Ventilation: A Manual of Recommended Practice.

What do I do if I need more information?

If you are an occupier that has an Industrial Refrigeration System and you need more assistance, there are a number of resources you can refer to:

Alternatively, you should engage the services of an Independent Dangerous Goods Specialist, who has experience in Industrial Refrigeration Systems.