Production of dense gas mixtures from ammonia releases — A review

Abstract Ammonia is a material of special importance in hazard control, because of its toxicity and its very widespread use. An additional factor is its ability to form denser-than-air mixtures on release to the atmosphere, in spite of its low molecular weight relative to that of air. Observational and theoretical evidence is reviewed that demonstrates the formation of such mixtures. It is shown that the combination of factors determining the density of the mixture is highly dependent on the mode of containment and the details of the mode of containment-failure; the physical properties of ammonia and the meteorological variables also have an important influence. Suggestions are made for investigations that are needed in order to improve the confidence with which a given release can be assigned to a particular density regime. A compilation of accidental releases of ammonia is included.