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Weathering or Aging
Weathering
or aging - Weathering is the easiest method of decontamination.
It acts on chemical agents through evaporation and decomposition. The
effects of weathering on biological and chemical contamination, however,
are variable. They depend on the persistency of the agent, climatic
conditions, and the type of surface. Therefore, exercise care with contaminated
areas until all vapor and transfer hazards are gone. Radiological contamination
is not affected by weather. Its hazards decay at a particular rate depending
upon the physical characteristics of the radioactive particles. This
process is called aging and it requires almost no labor and reduces
exposure to radiation. Although the radiation decreases with time, in
certain cases the contamination becomes more firmly fixed to the surface.
Effect
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Temperature - High temperature
speeds the change of liquid to vapor (evaporation) and hastens the dispersion
of chemical agents in the air. The persistence of liquid chemical agents
on the ground decreases as the temperature increases. Temperature han
no effect on radiological contamination.
•
Wind - Aeration aids in decontamination. High winds
rapidly disperse the vapors of chemical agents.
•
Humidity and rain - Moisture
tends to break down chemical agents. However, most chemical agents break
down very slowly. Heavy rain or sustained rain aids in removing contamination,
however, contamination may build up in drainage areas, creating hazards
there. Rates at which microorganisms dry out (dehydrate) depend on the
moisture content of the air. Although some agents (spores) possibly
are not affected by low humidity, periods of dry weather help reduce
most types of biological contamination within an area. Rain that wets
the terrain may prevent the formation of secondary chemical and biological
aerosols. Rainfall may also leach contamination into the soil.
•
Sunlight - Sunlight is a decontaminant.
Even in cold weather, the direct rays of the sun warm surfaces above
the air temperature. This hastens the evaporation and decomposition
of chemical agents. The ultraviolet and infrared radiation in sunlight
will kill most biological agents within one day.
•
Time - Radiological contamination
looses its radioactivity, hence its radiation danger, only with time.
The time required depends on the decay rate of the isotope(s) present
as contamination.
Earth
Earth
is a readily available natural decontaminant. The type of soil affects
the persistency of chemical agents. Sandy soil tend to absorb the agent
and increases the duration of the vapor hazard. Rocky soil does not
absorb the agent as fast, so it does not increase the persistency.
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Effect - Earth
is used to seal or cover contamination and to absorb liquid contamination.
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Procedures - Cover an area with
about 10 centimeters of earth. This offers protection against liquid
chemicals contamination as long as the earth is not disturbed and the
chemical agent is not exposed. Such an area may be crossed safely ,
but care must be taken not to disturb the earth covering. If the layer
of earth is broken, both a contact and vapor hazard may result. Extra
protection may be obtained by mixing household bleach with the earth.
In the absence of better absorbents, use earth to remove liquid contamination.
This earth however becomes contaminated and must be treated/disposed
of as contaminated waste. Material/items contaminated by nuclear radiation,
or by biological or chemical items. must be buried. For radiological
contamination earth is only a temporary cover. Land tracts, drainage
ditches, collection sumps contaminated by radiation can be efficaciously
sealed with at least 30 centimeters of earth. Eight centimeters of earth
will reduce the dose rate by approximately one half. If available use
earth moving devices to collect earth for sealing or burying, while
if mechanized equipment is not available people with shovels may decontaminate
small areas. |