The first enemy you meet: acclimatization and the mastery of desert heat

Infantry Magazine, Nov-Dec, 2004 by Michael Walter, Charles W. Callahan, Matt Hing

If you deploy to Operation Iraqi Freedom next summer, before your Soldiers cross the border and head north, they will face an enemy that has defeated a significant number of Soldiers moving into theater this year. Between July and August 2004, the hottest months in Kuwait, 134 Soldiers were reported as heat casualties in Kuwait and were lost from training. It is likely that the actual number is underreported by as much as 80 percent, and the true number of injured Soldiers may be as much as five times higher. The rate of reported heat injury per week peaked at 20 per 10,000 Soldiers in mid-July. Each heat casualty was lost to his or her unit for two or more days out of an already tight training schedule. Three of the Soldiers were likely lost to the fight permanently. These three developed heat stroke, two from the same unit within days of one another. They survived but were evacuated from theater, unlikely to return.

As the medical brigade in theater, we know in advance the schedule of units moving into the northern Kuwait camps. We could tell regardless when a new infantry unit moves into theater because of the bump in the number of heat injuries. Level II medical facilities at the camps typically began seeing heat casualties within the first week of the unit's arrival. The Soldiers we interviewed reported that they felt that exposure to heat in the summer months in the United States had prepared them sufficiently for deployment to Kuwait and Iraq. Nothing could be farther from the truth, as the conditions in the desert of Kuwait and Southern Iraq are not duplicated anywhere in the United States. We also heard more than once, "But I was drinking water, doc." Adaptation to this harsh desert environment is more than a matter of simple hydration. Water consumption is only one part of the process.

Soldiers in the desert are exposed to environmental heat stress through a combination of factors. Soldiers training vigorously in desert environments wearing individual body armor (IBA) and Kevlar generate heat from burning up to 6,000 kilocalories a day. (One kilocalorie is the heat energy needed to raise one liter of water one degree Celsius.) The Soldiers generate a great deal of heat, but unfortunately, desert conditions do not favor heat loss, which normally would occur through a combination of four different mechanisms.

Convection is heat transfer by the movement of a gas or liquid over the body. This is the primary means of the terrific heat loss that occurs with prolonged exposure of Soldiers to cool or cold water. A breeze feels cool in part from this effect. In the desert, the air may be as much as 30 degrees higher than the Soldier's body temperature. This July, the average temperature in the major Kuwait training range was 115 degrees (46[degrees] C) with a high of 135[degrees] (57[degrees] C), and the wind was typically up to 15 mph--a combination that results in significant heat stress.

Radiation is heat transferred from objects whose temperature is hotter than the Soldier: the sun, sky, large metal objects, or the ground. In Kuwait, from April to October the UV Index (ultraviolet index, a measure of the sun's irradiance in watts per meter squared) generally is in the "very high" to "extreme" range (8-11) and is typically 10 or 11. The mean UV Index across the southern United States in August is 7-9. The Soldier gains heat from the sun, from the heated desert sand, and the metal vehicles.

Conduction of heat is the transfer of heat though direct contact with an object. In the desert sands, heat is conducted through the ground and various combat equipment. For example, direct contact with surfaces exceeding 114 degrees produces pain and temperatures above that will burn in a very short period of time.

Heat loss from the body occurs primarily through the evaporation of sweat. The dry air of the desert, where the relative humidity is 10 percent, promotes the evaporation of sweat. However, sweat trapped near the body in cotton undergarments and uniform blouses below the IBA cannot evaporate due to lack of no air circulation. While adequate hydration insures that the Soldier will sweat enough, the mechanism is thwarted by a saturated uniform. In Soldiers who have not acclimatized adequately, sweat production will actually decline if the skin is wet, further blunting these cooling mechanisms.

Several large infantry and combat support units trained in Kuwait this summer in preparation of operation in Iraq. Most suffered significant effects from the heat. One unit evacuated as many as 10 percent of its Soldiers to the Level II facility in a single day.

However, medical surveillance of armed forces in Kuwait (conducted by 8th Medical Brigade) indicates that the 2nd Brigade Combat Team (BCT) of the 2nd Infantry Division was able to avoid significant heat injury altogether. Under the command of Colonel Gary Patton, the 2nd BCT deployed to Kuwait in late summer of 2004--peak months for heat injury. While a small number of Soldiers received intravenous fluids on firing ranges for treatment of volume depletion, there were no reported cases of heat exhaustion or heat stroke. The unit's overall approach to heat injury prevention has been primarily based on acclimatization.