Aircraft releases fire retardant. An airtanker releases fire retardant over land projected to be in the path of a forest fire. Fire retardants are normally composed of ammonium sulphate or ammonium polyphosphate with various additives such as thickeners, wetting agents and preservatives. They are often coloured red to indicate areas where the retardant has fallen. Photographed in 2000 in Wyoming, USA.