With the reduction in use of chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) gases in refrigeration and air conditioning systems has come an increase in the use of ammonia. Use of ammonia avoids the strong green house effect for which use of CFCs and HCFCs was banned, but it brings issues of it own. Much of the food we eat will have spent some time in storage chilled using ammonia.
The dual hazard of ammonia
In dry conditions, ammonia gas is lighter than air, but in wet or humid conditions, ammonia vapour can form. Ammonia vapour is heavier than air, so it behaves differently to the anhydrous (dry) gas form.
Ammonia gas will irritate the eyes and mucous membranes after only a short exposure to levels of around 200 parts per million (ppm) [More on exposure limits]. It is quite harmful if it reaches 1500ppm and the risk of serious injury becomes increasingly likely above 2500ppm. Between 16-27% (i.e. part per hundred) by volume, it also poses an explosive risk.
Understand the danger
Unless well-maintained, catastrophic ammonia leaks from refrigeration systems do occur, and deaths and injuries happen every year. Serious incidents have also been cause when pipes were ruptured by external forces, e.g. when hit by a forklift truck. Minor leaks from shaft seals, pipe flanges or valves, or during maintenance, happen as well. The risks of any escape will be site specific, and depends on many factors including (but not restricted to): size of leak; is it indoor or outdoor; nature and quality of ventilation; moisture in the atmosphere; does the leak present an explosive risk as well as toxic.
Plan to be safe
Because of its pungent smell and irritant nature, ammonia is not a gas that you can be near and unaware of. Even so, two gas detection sensors may be required, to detect in the toxic range and in the explosive range, to prevent entry into an unsafe environment.
Depending on the degree to which each of these factors comes into play, a different response may be required. A small leak may only warrant opening the windows and turning on ventilation to clear the air. Larger escapes may demand the temporary evacuation of an area or possibly the whole site with emergency services being required to attend.
Any site using ammonia systems must have an understanding of the risk factors as they relate to that site, specifically. Procedures for how they would handle system breakdowns on different scales must be developed. These procedures should be familiar to all relevant staff, so everyone knows what to do in the unlikely event of a leak.
For personal protection from ammonia view our Tetra 3 multigas detector
Or view this document for some helpful advice on Ammonia site evacuation.