Characteristics of Blister Agents

The severity of blister agent effects will, in part, be affected by environmental conditions.

• Warm, humid conditions increase the severity of blister agent damage and shorten the time of symptom onset.
• Cold weather retards the time of symptom onset and, providing the exposed skin remains cold, lessens the severity of blister agent damage.

Blister agents are heavier than air.

• Mustard has a vapor density 5.4 times greater than air.
• Lewisite a density 7.1 times greater.
• HL is 6.5 times heavier than air.

The more dense a vapor, the more it flows to low spots such as valleys, depressions, basements, or ground level.

Mustard Lewisite (HL)

The effect of HL liquid on the eyes and skin, or vapor in the eyes or respiratory tract, is immediate. HL causes intense pain and lid twitching in the eyes. Within an hour, edema of the conjunctivae and lids begins and rapidly results in eye closure.

The casualty feels stinging pain within seconds after contact with liquid HL. The pain causes the casualty to decontaminate rapidly. Rapid decontamination is the only way to avoid severe burns. After five minutes of contact with HL, the upper layer of skin (epithelium) will die and appear gray. Painful erythematic will begin shortly afterwards, and painful blisters may appear within 12 hours.

The immediate irritation from HL vapor is so intense that an individual must immediately mask or exit the area. Respiratory casualties may be unable to do either. Pulmonary effects are similar to those caused by mustard alone, except that pulmonary edema (fluid in the lungs) is more likely after Lewisite.