The aim of this paper is to study the effectiveness of the water curtains used by firemen in France to protect people fighting chemical spillage. The effectiveness of these barriers is a reduction in concentration behind it by a factor of 10 at a distance of approximately 13 m and a factor of 3 at a distance of approximately 20 m in the case of ammonia releases. The results of similar studies of a wide variety of toxic gases will provide a quick and reliable tool for firefighters, which will help to define at what distance to place the curtain and predict the concentrations behind it.