be liquified. The boiling point of this liquid is -33?C. Under certain circumstances, liquid ammonia can form a denser-than-air mixture at atmospheric conditions. If, upon release, there is substantial entrainment of fine liquid ammonia droplets with the air, and these cool below the ambient boiling point, then a dense ammonia cloud may occur.
For humans, the ammonia concentration at which 50% of an exposed population would die after 30 minutes is 11,500 ppm. Fortunately however, the chemical's odor threshold is very low (i.e., 5 ppm). It takes ammonia concentrations of more than 5000 ppm to cause severe pathophysiologic effects.
Ammonia gas per se is not poisonous. It is the chemical's solubility characteristics that enable it to cause significant harm. Ammonia dissolves readily in water to form ammonium hydroxide. This compound then dissociates into caustic hydroxyl ions. For the most part, ammonia severely irritates moist surfaces such as the lungs, eyes, and skin. In addition, the formation of ammonium hydroxide is an exothermic reaction. Therefore, ammoni
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