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classification as Type III (systemically distributed) agents. Finally, some agents such as
sulfur mustard exhibit both local (in this case, initially Type I) and systemic (Type III)
effects, although the systemic effects of mustard (which may include bone-marrow
depression and resulting pancytopenia) become clinically significant only after a delay.
Although not stockpiled in the United States for military purposes, chlorine, phosgene,
and hydrogen cyanide are common components in industrial manufacturing. Primarily
liquids, they are easily vaporized, allowing for widespread gaseous dispersion.
Clinical Effects
The significant morbidity from pulmonary agents is caused by pulmonary edema. With
chlorine, edema may appear within 2–4 hours or even sooner with more significant
exposures. Radiologic signs lag behind clinical symptoms: pulmonary interstitial fluid
must be increased 5- to 6-fold to produce Kerley B lines on a chest radiograph.
Pulmonary edema may be exceptionally profuse; in a study from the 1940s, pulmonary
sequestration of plasma-derived fluid could reach volumes of up to 1 L/hr. This problem
may be exceptionally profound in children, who have less fluid reserve and are at
increased risk of rapid dehydration or frank shock with the pulmonary edema.
Additionally, because children have a faster respiratory rate, there is exposure to a
relatively higher toxic dose.
Chlorine. Chlorine is a greenish yellow gas that is denser than air and, therefore, settles
closer to the ground and low-lying areas. This may have significant consequences for
small children and infants, who would be exposed to higher concentrations of the vapor
and thus receive higher inhaled doses of the agent. Chlorine has a strong, pungent odor
that most people associate with swimming pools. Because the odor threshold (at 0.08
ppm) is less than the toxicity threshold, the odor may warn individuals that exposure is
occurring.
The initial complaints in chlorine exposure may be either intense irritation or the
sensation of suffocation, or both; the suffocating feeling is what led to its characterization
as a “choking” agent. Low-level exposures to chlorine result in mucosal irritation of the
eyes, nose, and upper airways. Higher doses lead to respiratory symptoms that progress
from choking and coughing to hoarseness, aphonia, and stridor—classically Type I
effects. Dyspnea after chlorine exposures indicates damage to the peripheral
compartment (Type II insult) and incipient pulmonary edema.
Phosgene. Like chlorine, phosgene is also heavier than air, thus posing an increased risk
for children who are exposed. Phosgene itself is colorless, but associated condensation of
atmospheric water produces a dense white cloud that settles low to the ground. It has the
characteristic odor of newly mown hay. However, the odor threshold for phosgene (at 1.5
ppm) is higher than the toxicity threshold, and unlike the case with chlorine, detection of
the odor would be inadequate and too late to serve as a warning against toxic exposure.
Phosgene is primarily associated with the development of pulmonary edema. However,
because in low to moderate doses it does not cause the mucosal irritation associated with
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