Figure 5-9.Chemical contamination carried by the wind.
Some chemical agents are designed to contaminate
the air and to cause disabling or lethal casualties when
the vapor is breathed or contacts the skin or eyes. These
are called air-contaminating agents. Air-
contaminating agents generally form a gas cloud that
moves with the wind currents. However, some
chemical agents readily diffuse through the air and
spread out from an attack area even in calm winds. Air-
contaminating agents may be classified as either
persistent or non-persistent. When an unknown type of
chemical agent is used, it is always considered an air-
contaminating agent until otherwise identified.
Other chemical agents (a solid or liquid) may be
spread over an attack area to contaminate the ground
and other surfaces. To some extent, the solids or liquids
emit a hazardous vapor. Direct contact or close
proximity to the contamination may cause disabling or
lethal casualties. These types of agents are known as
ground-contaminating agents. The normal downwind
hazard distance of any ground contaminating agent
used at sea is assumed to be 10 nautical miles.
Various chemical agents are known to be ready for
use by countries that do not accept or ignore the Geneva
Conventions agreement prohibiting the use of chemical
weapons. After a chemical agent has been used in the
field, the chemical may be classified by agent groups
based on the effects of the agent on the human body.
Agent groups include nerve, blister, blood, choking,
incapacitating, irritant, and vomiting. Survey teams
may perform tests to determine the composition of an
agent. After testing, the agent may be identified by
name, such as Tabun, Sarin, Soman, Mustard, or
Lewisite. NBC protection, varying from use of gas
masks to wearing complete NBC suits, depends on the
agent group and specific agent employed. Further
information on chemical agents and protection is
contained in the Military Requirements for Petty Officer
Third Class training manual.
When a suspected chemical weapon is employed
against your location or ship, you first must complete
personal and shipboard protective procedures. As the
weather observer, you must then report current
meteorological conditions to your shipboard Combat
Information Center, or ashore, to Base Operations or the
local NBC center.
Weather conditions that are required for the
evaluation of the chemical agent downwind hazard
distance (DHD) and the duration of the hazard are as