Lesson 1/Learning Event 4
freezing perspiration collects and cannot evaporate. Protective masks must be equipped with
winterization kits to insure continued serviceability. Nerve agent antidote injectors must be kept inside
the outer garment to prevent freezing. This consideration also applies to the reagents in the chemical
agent detector kits. Decontamination will be difficult because washing with water will not be feasible.
Some of the standard decontaminating materials may be used at lower temperatures for limited
decontamination of equipment.
Temperatures can be extremely important in the persistency of chemical agents. In warm temperatures,
the rate of evaporation will shorten the time that a liquid chemical stays in an area, while at cooler
temperatures the agent will remain for a longer period. Some liquid chemical agents will freeze at low
temperatures. When exposed to heat such as in a warm-up tent, these agents thaw and again become
Effects of Humidity and Precipitation on Chemical Agents. High humidity
and precipitation alter the
effects of chemical agents differently. For example, high humidity increases the effectiveness of HD but
does not influence the effectiveness of GB. Heavy or lasting rains wash away liquid chemical agent
contamination. Some agents may then collect in low areas and stream beds and present a lingering
hazard. Light rainfall occurring hours after VX contamination can cause recurrence of a contact hazard.
vapor concentration above the contaminated area. A moderate or heavy fall of snow over a layer of
previously deposited chemical agent may allow comparatively safe movement across the area until the
layers are churned up or melted. A chemical agent deposited on the snow, however, presents an
immediate contact hazard.
In addition to the washing away effect of precipitation on chemical agents, the hydrolysis effect must
also be taken into consideration. Hydrolysis is the reaction of any chemical substance with water,
whereby decomposition of the substance occurs and one or more new substances are produced.
Hydrolysis is of great importance in chemical operations. Because of the hydrolysis effect phosgene and
lewisite will not be a great threat when the relative humidity is above 70 percent. Hydrolysis of lewisite,
however, produces a material which is still toxic.
Operations in a Chemical Environment
When units or survey personnel operate in a chemical environment, their actions are governed by the
nature of the threat the mission, the situation, and the weather. Maneuver of troops and movement of
supplies should be planned so that contaminated terrain is avoided to the maximum extent possible
consistent with the security and mission of the movement. Contaminated