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posted Feburary 15, 2006
According to its thermodynamic qualities, ammonia is one of the best refrigerants presently known. Ammonia does not deplete ozone layer and does not directly contribute to the increase of greenhouse effect. There are, however, acute human dangers associated with ammonia.
Ammonia is lighter than air, but still can pose an asphyxiation hazard if workers/rink users are incapacitated during an accident (leak) or are unable to exit for other reasons. While it will disperse fairly rapidly outdoors, ammonia can be trapped in a machinery room with ventilation at floor level. Ammonia also can be corrosive to the skin and eyes in high concentrations. Its irritation level is such that people will vacate the area quickly, if they can, if a significant leak occurs. Ammonia has a distinct and pungent smell that can be detected at concentrations far below that which is harmful to the human body. For this reason, ammonia is often referred to as the self-warning refrigerant.
Ammonia is a chemically reactive gas that is very soluble in water. Ammonia is characterized by a typical pungent odour and is detectable by most people at levels of about 50 ppm in the atmosphere. At 400 ppm, most people experience immediate nose and throat irritation, but suffer no permanent ill-effects after 30-60 minute exposure. A level of 700 ppm causes immediate irritation to the eyes, and a level of 1,700 ppm (0.17%) will give rise to repeated coughing and can be fatal after about 30 minutes exposure. Exposure to concentrations exceeding 5,000 ppm for quite short periods can result in death.
Ammonia gas has an explosive range of 16 to 25 per cent by volume in air. Although it is classified as non-flammable under WHMIS (Workplace Hazardous Materials Information System), its flammability potential is only slightly less than that of some gases that do meet the official flammability criteria.
Contact of ammonia with certain chemicals--including fluorine, chlorine, bromine, iodine, mercury and silver oxide--can create explosive compounds. Moist ammonia will vigorously attack silver, copper, zinc and many of their alloys. Aluminum is attacked to a lesser extent. Iron and steel are inert to ammonia.
Under normal circumstances people will not be able to bear ammonia concentrations at even a fraction of the flammable limit. The appropriate precautions are mainly those applicable in populated areas and in work situations where sudden exposures are foreseeable, such as maintenance and repair work, including in particular filling and oil draining. Precautions against fire and explosion will be appropriate however, in unoccupied areas such as compressor houses and unattended plant such as cold stores where accumulations of vapour may go unnoticed.
It is essential that a clear emergency procedure is drawn up which details the precise duties of all staff and the arrangements for evacuation, rescue, first aid, plant isolation, etc. It is particularly important that evacuation procedures are clearly set out and regularly practised where refrigeration systems are in working areas. A common method is to use the fire alarm, provided that actuating points are immediately available at working areas. Personnel should be warned not to approach any vapour clouds. (Clouds may often look like steam because of the cooling of the released gas).
Adequate exits should be maintained from plant rooms at all times. Personnel seriously affected by an ammonia escape suffer streaming eyes and violent coughing and rapidly become disorientated. They therefore require clear prior knowledge of a safe exit route.
Research by Corey Chivers