Liquids - When a chemical agent is used for its liquid effect, evaporation causes the agent to form into a vapor. Depending on volatility, vapor clouds, which tend to stand near the surface because of high vapor density, are usually of low concentration and have about the same temperature of the surrounding air. Furthermore, vapor density governs the extent that the vapor will mix with air. Persistence agents are those with high vapor density impact at ground level with very little evaporation of the same, and while drops are airborne, and after impacting, the liquid continues to evaporate. The rate at which the liquid will evaporate at a given temperature and pressure is governed by the agent vapor pressure. Initial concentrations are lower, since the vapor source is not instantaneous as a vapor agent is, but evolves over a long period until the liquid source is expended. Liquid agents may be absorbed, being taken in through the pores of a surface, and adsorbed, i.e., accumulated on a surface of a solid, and they may also evaporate. Desorption, i.e., changing from an adsorbed state to a gaseous state and going back into the air, begins as the liquid is no more present on the surface. The vapor concentration over areas contaminated with a liquid agent tends to be less than with newly formed vapor clouds, and downwind agent concentrations are not nearly as great as with other types of agents.

Chemical agents [1] may be grouped according to use as follows:
• Toxic Chemical agents: capable of producing incapacitation, serious injury, or death.
Chemical compounds [1] may be grouped according to use as follows:
• Chocking agents: chemical agents causing irritation and inflammation of bronchial tubes and lungs. Their primary physiological action is limited to the respiratory tract, with injury extending to the deepest part of the lungs.
• Nerve agents: chemical agents which, when absorbed into the body by inhalation, by ingestion, or through the skin, affect body functions by reacting with an enzyme (cholinesterase) throughout the body, permitting accumulation of a stimulator (acetylcholine). The major effects are:
1 - Those on voluntary nervous system; e.g., muscle stimulation with uncoordinated contractions, followed by fatigue and eventual paralysis.
2 - Those on the parasympathetic nervous system; e.g., pinpointed pupils; bronchial constriction; nausea, vomiting and diarrhea; secretion of the glands of the nose, mouth, bronchi, and gastrointestinal system.
3 - Those on the central nervous system; e,g., disturbances in thought, convulsion, coma, and lethal depression of the vital centers of the brain.
• Blood agents: chemical agents which when absorbed into the body primarily by breathing, affect body functions through action on an intracellular enzyme called cytochrome oxidase. This stops normal metabolism in every cell in the body, and thus the cells are unable to use the oxygen brought to them by the blood. The body tissues are rapidly damaged by this failure to utilize oxygen.
• Blister agents: chemical agents that are readily absorbed by both exterior and interior parts of the body, causing inflammation, blisters, and general destruction of tissue. The agent vapors, besides affecting the skin, attack the respiratory tract; the effects are usually more severe in the upper tract. Eyes are very susceptible to blister agents.
• Defoliants and herbicides: plant growth regulators and desiccants, these agents have a hormonal effect on plant organisms, i.e., forcing unnatural growth or causing leaves and shoots to die.

[1] The list includes only chemical agents or compounds of strictly military importance.