Lesson 1/Learning Event 4
Behavior of Chemical Agents in the Field
Knowledge of the behavior of chemical agents in the field is necessary for the success of defensive
operations in a chemical environment. NBC defense planning is integrated into the planning for any
operations in a chemical environment. Consideration must be given to the way weather and terrain in
the area of the operation affect the needs for NBC protection. Weather also affects chemical agents and
can have a great influence on the likelihood that threat forces will employ chemical agents.
Threat forces' delivery systems can deliver massive concentrations of chemical agents in either
persistent or non-persistent form. These agents are designed to injure or kill personnel, but they are
dependent on terrain and weather for maximum effect.
Effects of Terrain Contours on Agents. Topography influences the wind by thermal effects and by
physically diverting and altering the normal flow of wind. Under stable conditions, chemical agent
clouds tend to flow over rolling terrain and down valleys. Dangerous concentrations persist in hollows,
low ground, depressions, and foxholes. This is the reason these features receive special attention in
surveys. Chemical clouds tend to go around such obstacles as hills. In rough ground, including that
covered with tall grass or brush, chemical agent cloud movement is retarded and the agent collects on
the vegetation. Flat country (unless it is covered with tall grass or brush) allows an even, steady
movement.
Effects of Temperature on Chemical Agent Effectiveness. Chemical agents employed during high
temperatures will normally be less persistent, but the effect on personnel within the target area probably
will be much greater for several reasons. The protective mask, worn to protect against inhalation of
agent vapors, is uncomfortable in hot weather. Protective clothing designed to protect the skin is very
warm when worn properly. Even well-trained personnel will have difficulty remaining masked for long
periods of time. If protection is decreased, the risk of chemical casualties is increased. In either case, a
casualty is a casualty and detracts from the unit performance. Discipline and leadership by officers and
NCOs will be required under these conditions. Personnel will have a tendency to perspire during warm
temperatures, making it easier for chemical agents to be absorbed by the skin.
Threat use of chemical agents will be degraded in low temperatures because of the difficulty of
establishing a casualty-causing concentration in vapor or aerosol form. Cold also slows the absorption
of agents through the skin and the heavy clothing helps to prevent skin contact. Troops wearing
protective clothing will not suffer the degree of heat build-up common in warmer areas. They may
become cold casualties from hypothermia, however, because
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