To meet military specifications (for pour point1 and cloud point2), fog oil historically has been produced from naphthenic oils. The composition varies from batch to batch from different sources and even from the same source. Samples taken from two sources of conventionally refined fog oil contained approximately 50% aromatic hydrocarbons, 1% acids, alcohols and esters, and nitrogen derivatives in the parts-per-million range (Katz et al. 1980). Only slight variation in chemical composition results from the smoke-generation process (Katz et al. 1980). The severely refined fog oil that is in use today should not contain detectable quantities of many aromatic hydrocarbons.
Fog-oil smoke is a condensation aerosol (a mist) composed of liquid particles. Condensation aerosols are, in general, relatively small in aerodynamic size and respirable and are generated to obscure soldiers from view. A fraction of the oil (components with low boiling points) might remain in the vapor form. All measurements of fog-oil smoke reported or recommended in this chapter are referred to in milligrams of total particulates per cubic meter.
The chemical and physical properties of fog oil are similar to those of lubricating and petroleum-based cutting oils. Substances added to cutting and lubricating oils to maintain their physical properties during use under extreme pressure and heat are responsible for the distinguishing characteristics of these oils. Although little information is available regarding the health effects of fog oil, inferences can be drawn to a large extent from the health effects of lubricating and mineral oils. However, only certain cutting oils would be appropriate in making such a comparison. Insoluble cutting oils composed of mineral oils with only small quantities of additives should have biological properties similar to fog oil.