The mixture of particles, liquids, and gaseous compounds found in smoke from wildland fires is very complex. The potential for long-term adverse health effects is much greater because of this complex mixture. The particles are known to contain many important organic compounds some of which condense to form tarry droplets over a substrate material of ash or graphitic carbon or both. The size distribution of smoke particles is such that a large percentage are respirable. Gaseous compounds in the air adjacent to fires in association with the particles include carbon monoxide, methane, oxides of nitrogen and many organic compounds-some of which are carcinogens and many of which are irritants. Other semi-volatile compounds have a significant vapor pressure at ambient temperature and pressure which results in a gas phase emission and many of these compounds are important from a health standpoint, but have not been adequately quantified. With the additional data of today, we still do not know what the overall toxicity of smoke is from wildland fires or how this toxicity varies from fire to fire. The large variance in the concentration of smoke needs to be evaluated to assess the level of exposure and risk to fireline personnel. The new PM2.5 air quality standard is designed to protect human health and suggests that health is most at risk from particles less than 2.5 micrometers in diameter. Along with the combustion products is the dust, heat, and remoteness of many of the wildland fires and fire camps. The fire, fuel, and weather vary continuously, which changes the fire dynamics and the dilution occurring in the work environment. The smoke may be extremely dense for a few minutes to several hours or days with the air being relatively clean at other times. Most of what is known about smoke has been inferred from research done with prescribed fires and from fires burned under carefully controlled laboratory conditions. Many measurements have been made of exposure of firefighters to CO and a few other compounds and the CO has been correlated with some compounds. This paper discusses measurements that have been made, correlations with other compounds, and ratios of compounds to CO (including particulate matter). The link below refers to part 2 of the document titled, Health Hazards of Smoke: Recommendations of the April 1997 Consensus Conference. Please scroll down to page 12 for this paper.