Its extremely high alkalinity (pH≥12.4) causes anhydrous ammonia gas to release ammonium hydroxide upon contact with the moisture in human tissue, and thus results in a 3.2mg/(cm²·min) rate of denaturation of corneal protein, as was proven in a Journal of Toxicology study conducted in 2023. Exposure to 300ppm for 5 minutes could increase the ocular surface pH level from 7.4 to 9.5, causing irreparable burns. Its density in vapor form (0.597kg/m³, air = 1) leads to the formation of a persistent aerosol band at 0.5-1.2m height on the ground. In the Dezhou Chemical plant leak accident in 2021, 50m from the leak point, the measured concentration was still 180ppm, exceeding 60% of the IDLH (immediate life threatening concentration) value of 300ppm.
In terms of injury to the respiratory system, the hydrating of the anhydrous ammonia gas in the alveoli formed NH4OH, which was seven times quicker at breaking down the surfactant phospholipid layer, leading to a reduction of 60% in the effective alveolar exchange area. US NIOSH data report 500ppm environment exposure for 10 minutes to achieve a probability of laryngeal edema equal to 78%, whereas 30 seconds exposure to a concentration of 2500ppm through respiratory uptake can lead to death, LC50 (50% lethal concentration) = 7337ppm·5min, which is extremely low compared to chlorine gas (850ppm·5min). In a 2013 Iowa Agricultural co-op accident, three employees were exposed to 50kg of liquid ammonia vapor spilled in a closed space (20m³) (the peak concentration was 2000 PPM), and their blood oxygen saturation fell to 72% within 2 minutes, ultimately succumbing to acute respiratory distress syndrome.
Neurotoxicity showed that when blood ammonia concentration was higher than 50μmol/L, astrocyte glutamine synthetase activity was downregulated by 83%, and the risk for brain edema increased to 19 times normal. The Health and Safety Executive (HSE) of the UK reported a 34% increased rate of cognitive impairment and a 21% decrease in memory accuracy for workers with continuous exposure to 25ppm (OSHA PEL standard). Maximum level of ammonia in blood of affected villagers in 2020 India pesticide factory leak disaster was 180μmol/L, causing tremor, disorientation and other neurological sequels in 36% of exposed individuals.
In environmental toxicity, a one-ton leakage of anhydrous ammonia gas can increase the pH of water within a radius of 300m to 9.8, leading to a 500% increase in fish gill filament mucus secretion and a 72% reduction in oxygen exchange efficiency. The Norwegian Institute of Marine Research experiment showed that 0.2mg/L concentration of ammonia nitrogen for 48 hours caused 95% mortality of salmon fry. With 0.28 times CO₂ greenhouse potential (GWP), the nitrate aerosol generation to atmospheric residence ratio is 5-7 days and is 0.67, which accelerates the PM2.5 formation rate by 23%.
Emergency response information shows that 2% boric acid solution should be irrigated into the eyes immediately and within 10 seconds of contact, and delayed action beyond 30 seconds will extend the cycle of corneal repair to 6 months from 14 days. US CDC recommends the location of the accident must be forced ventilation with wind speed ≥3m/s, and the time of purification is exponentially related to the number of air changes in order to dilute the concentration to the safe level of 25ppm. When ACH is 12 times, the purification time of a room of 50m³ can be reduced from 45 minutes to 8 minutes. The smart sensor network introduced by the Port of Singapore in 2022 condensed the leak response time to 9 seconds effectively by monitoring the real-time ammonia concentration at 300 points (accuracy ±1ppm), 40 times more efficient than traditional manual inspection.