Anhydrous ammonia gas leakage is a direct human health hazard. Its IDLH concentration is 300 ppm. It will burn the respiratory tract on exposure to it for 15 minutes. The mortality rate is up to 60% if the concentration level exceeds 500 ppm. For example, in 2013, 2.5 tons of liquid ammonia (850 times volume expansion rate) leaked at an Iowa, USA, fertilizer plant and resulted in 8 deaths, 120 people hospitalized, and a direct medical cost of more than $2.3 million. Experiments have shown that under unshielded conditions, 5-minute exposure to 100 ppm ammonia gas causes corneal ulcers, TLV-TWA (weighted average 8-hour threshold) is only 25 ppm, and the probability of leakage accidents in industrial processes is 0.17 times/kiloton · year.
Regarding environmental risks, 1 liter of liquid ammonia (0.68 kg) drains into 1,360 liters of gas with a diffusion range of 500 meters, and the water pH rises quickly over 11.5, and 90% of fish die. In 2019, in the Maharashtra state of India, an ammonia storage tank burst releasing 4.8 tons of ammonia gas and polluting 12 hectares of agricultural land by making the content of ammonia nitrogen in the soil more than 40 times greater than normal for $740,000 to be repaired. Its atmospheric residual time is about 7 days, and the probability of reacting with NOx to produce PM2.5 increases by 23%, and according to EPA statistics, the ecological loss caused by each ton of ammonia leakage is estimated at about $85,000.
In terms of explosion hazard, the explosion limit of ammonia is 15%-28% (volume ratio), and the minimum ignition energy is 14 mJ. In 2021, Ludwigshafen, Germany, a chemical factory released 1.2 tons of ammonia by valve failure, led to explosion in the event of an electrical shock, with 0.8MPa intensity of shock wave, collapsed the buildings in 150 meters radius, with direct financial damage of 14 million euros. NFPA 704 classifies it as a level 1 fire hazard, but it goes up to level 3 for the risk index if combusting materials are blended, and there is a higher possibility of explosion up to 34% when leakage rate is >2 kg/s.
In terms of equipment corrosion risk, ammonia forms ammonium hydroxide when humidity is >10%, and the rate of corrosion in copper alloy is up to 0.5mm/year. A Canadian refrigeration cold chain company resulted in a yearly loss of 0.3 tons due to defects in welding of the pipeline, to the refrigeration system compressors resulting in corrosion failure, which raised maintenance cost by 270% over normal maintenance, and life fell to 9 years from 15 years. ASME B31.3 recommends 20% extra thickness of the pipe for ammonia but when inspection is due after more than 6 months, there are 18% chances of leakage.
As regards economic and legal risk, the U.S. OSHA caps overpressure leak fines for ammonia releases at $15,625 per incident, to $156,259 in the event of a fatality. In 2020, the Texas chemical storage tank facility was fined $830,000 and resolved civil damages for $23 million for an overpressure leak from a storage tank. An ammonia infrared monitoring system ($50,000 per unit) can reduce leak response time from 30 minutes to 90 seconds, reduce accident rates by 76%, and provide a 140% return on investment. According to NIST, the combination of a smart valve (response time 0.5 seconds) and a pressure sensor (accuracy ±0.1 bar) can reduce the likelihood of a large leak by 98%, avoiding a potential loss of $27 million for every million dollars of safety investment.