causing pulmonary edema, are classified as choking agents.
Best known of
these agents is phosgene. Agents in this class are called choking agents
because irritation of the bronchi, trachea, larynx, pharynx, and nose may
occur and, with pulmonary edema contribute to the sensation of choking.
Blister agents and certain systemic agents also may injure the respiratory
tract. Since the action of phosgene is typical of the choking agents, it is
used as the example in this part of the lesson. Persons exposed to phosgene
need not be withdrawn during combat unless signs of pulmonary distress
The medical officer should advise the responsible commanding
a. Choking Agent (CG).
At ordinary temperatures and atmospheric
pressure, phosgene is a colorless gas. It has an odor resembling that of
new-mown hay, grass, or green corn. It is readily condensed by pressure or
lower temperature to a colorless liquid which boils at 46F.
Phosgene reacts rapidly with water to yield nontoxic hydrolysis products.
Its concentration in air is reduced by water condensates (rain, fog) and by
It is known as a nonpersistent chemical agent which
exerts its effects solely on the lungs, and results in damage to the
capillaries and scarring of the lungs.
It causes seepage of watery fluid
into the air sacs.
When a lethal amount of CG is received, the air sacs
become so flooded that air is excluded and the victim dies of anoxia (oxygen
The severity of poisoning cannot be estimated from the
immediate symptoms, since the full effect is not usually apparent until 3 or
4 hours after exposure. Most deaths occur within 24 hours.
CG is used as a delayed-action casualty-producing agent although immediate
symptoms may follow exposure to high concentrations of CG. A standard field
protective mask or a gas-particulate filter unit (collective protector)
gives adequate protection against choking agents.
Detection of phosgene
prior to contamination can be accomplished by using the M8 or M18A2
Automatic Chemical Agent Alarm System and odor.
Decontamination is not
required under field conditions.
The M8 Automatic Chemical Agent Alarm System will detect only
blood, nerve, and choking agents.
b. Choking Agent (DP). Choking agent DP (Diphosgene) has a much higher
boiling point than CG. DP is slightly lacrimatory, therefore, DP has less
surprise value than CG when used on troops.
Furthermore, its lower
volatility adds to the difficulty of setting up an effective surprise