HD is heavier then water, but small droplets will float on the water surface and present a hazard. Heavily splashed liquid mustard persists one to two days or more in concentrations that produce casualties of military significance under average weather conditions and a week to months under very cold conditions. HD on soil remains vesicant for about two weeks. The persistency in running water is only a few days, while the persistency in stagnant water can be several months. HD is about twice as persistent in sea water.
Mustard acts first as a cell irritant and finally as a cell poison on all tissue surfaces contacted.
Blistering or ulceration is also likely to occur. Other effects may include vomiting and fever that begin around the same time as the skin starts to redden. HD causes casualties at lower concentrations in hot, humid weather, because the body is moist with perspiration. Wet skin absorbs more mustard than does dry skin. Individuals can be protected from small mustard droplets or vapor by wearing protective masks and permeable protective clothing.