Coffee Break Training: Hazardous Materials: Vapor Pressure, Boiling Point, and Vapor Density [open pdf - 458KB]
"Approximately 90 percent of hazardous materials (hazmat) injuries are due to inhalation. In general, although some solids are very hazardous (on physical contact with skin or if ingested into the body), gases and liquids with high vapor pressures pose the highest risks to responders. These chemicals are more dangerous because they have the capability to become airborne, to disperse and travel through the atmosphere and to be inhaled. Vapor pressure (Vp), boiling point (BP) and vapor density (Vd) are three physical properties that are significant in determining risk. All liquids give off some vapor at their surface. The amount of vapor given off by a liquid at a given temperature and pressure is measured as that chemical's Vp. Vp is the force exerted by a vapor against the sides of a container or against atmospheric pressure. Chemicals that have high Vps have a greater tendency to vaporize than those with lower Vps. A chemical is said to be more volatile if it has a greater tendency of a chemical to vaporize."
Coffee Break Training - Hazardous Materials Series No. HM-2012-3
United States Fire Administration: http://www.usfa.fema.gov/