Table 2-1. Weather and Time Factors for Disposal of Chemical Munitions

TM 9-1300-277

agent clouds released under lapse conditions tend to

(2) Volatility. There are several factors which

dissipate more rapidly than under neutral or inversion

influence the period of time a chemical agent will exist

conditions. Obviously, disposal work is best conducted

at the point of its release. Volatility is important in

under lapse conditions whenever possible.

determining the persistency effect of an agent. Volatility

varies directly with temperature. A liquid or solid

(4) Wind speed. Persistency is also affected

chemical having high volatility will evaporate or turn into

by wind speed. As wind speed increases, the chemical

a gaseous state more rapidly than a chemical of low

agent cloud covers the downward hazard area more

volatility.

rapidly; however, the cloud will diffuse sooner and thus

travel a shorter total distance. Buildings, vegetation,

(3) Temperature gradient. The temperature

large bodies of water, contour of the land and other

gradient also effects the persistency of a chemical

terrain features play an important role in the duration of

agent. Temperature gradient is the difference obtained

effectiveness of agent at its point of release and its

by subtracting the air temperature 0.5 meter (1.6 feet).

diffusion downwind. Any obstruction to the movement

above the ground from the air temperature 4 meters (13

of air creates turbulence which breaks up the clouds.

feet) above the ground. If the temperature at 4 meters

(13 feet) is greater than that at 0.5 meter (1.6 feet), an

(5) Rain and humidity. Rain and humidity

inversion or stable atmospheric condition exists.

vary in their effect on chemical agents. Depending

Conversely, if the temperature at 4 meters (13 feet) is

upon the chemical involved, rain can hold the cloud

less than that at 0.'5 meter (1.6 feet), a lapse or unstable

close to the point of release or wash the chemical from

atmospheric condition exists. If the difference is 1

the air. Moisture from rain or high humidity will cause

degree or less, a neutral condition exists. Chemical

some chemicals to break down through hydrolysis.

Table 2-1. Weather and Time Factors for Disposal of Chemical Munitions

Factor

Condition

Excellent

Fair

Fair*

Unsatisfactory**

Temperature

75 and above

55 - 75

Under 55

Sky

Clear

Partly Cloudy

Clear

Cloudy

Wind

4 mph - 15 mph

5 mph - 20 mph

7 mph - 15 mph

Under 3 mph or

over 20 mph

Time of Day

1000-1600

*This column pertains to winter conditions. When the ground is covered with snow, however, the disposal of toxic agents

and munitions is not feasible.

**Chemical agents or munitions will not be disposed of under these conditions but only when extreme emergency

conditions prevail.

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