The suit -- available in navy blue and multicolor camouflage for either deserts or forests -- fits snugly over a regular uniform; a hood flips over a gas mask and the arm and leg cuffs seal over boots and gloves. The suit's outer layer resists water, oil and toxic dangers; the activated-carbon lining is designed to absorb any toxic agents that manage to get through, while allowing some body heat to escape.
"Our commanders understand what heat's all about, and they understand what heat stress is all about," said Brig. Gen. Steve Reeves, the Defense Department's executive officer for chemical and biological defense.
A Modular System
The JSLIST and the rest of the protective ensemble are a modular system, designed to be pulled on as needed depending on the threat level. Everything depends on what the military calls the "mission-oriented protective posture," or MOPP, level.
MOPP1 corresponds to a possible but not imminent threat. Soldiers wear the jacket and pants but carry the hood, mask, gloves and boots. For MOPP2 -- when a chemical or biological attack is deemed probable -- the protective over-boots are then pulled on. When toxic agents are detected at low levels, a MOPP3 alert requires soldiers to don the mask and hood, still carrying the gloves. The gloves are added at MOPP4, when the environment may be badly contaminated.
All troops in the gulf region carry a suit at all times -- even sailors are required to wear olive-green pouches containing the JSLIST. On the aircraft carrier Abraham Lincoln, they are called "Wilsons," after Tom Hanks' omnipresent Wilson volleyball sidekick in the film "Castaway."
Comments such as, "I'm getting a bruise from my Wilson," or, "I can't wait to get rid of my Wilson" are commonly overheard from sailors tired of carrying them around.
Lugging a Wilson around is only a minor inconvenience compared with the headaches of actually working in one.
Female troops are in a particularly bad spot. Lt. Suzanna Cigna, aboard the Abraham Lincoln, said women have been told by trainers that the suit is not designed to allow them to urinate without risking exposure to outside contaminants. On the other hand, if they relieve themselves while in the suits, the urine destroys the protective carbon lining.
"I guess we're just supposed to hold it," Cigna said.
Troops faced with MOPP4 conditions would be moved to a safer location as soon as operationally feasible, said Lt. Col. Daniel Murray, executive officer of the U.S. Army Chemical School at Ft. Leonard Wood in Missouri. But they are expected to function in full protective gear for at least six hours, and have trained to do so, he said.
That's difficult for Cigna to fathom.
"After half an hour, I was so drenched in sweat that there were puddles in my boots and the fingertips of my gloves," she said of her time training in the suit. "I can't imagine what it would be like for hours or days."
The implications of the heat problem can be ominous.
If the core body temperature rises too much, it "poses the risk of major arrhythmia [irregular heart beat] or cardiac arrest," said Davies, the heat expert at Baylor. "The same sort of difficulties arise in the brain, [leading to] giddiness, sometimes hallucinations, sometimes profound weakness or fatigue," and ultimately collapse.
If troops in toxic areas do light work, such as monitoring a position and occasionally firing a weapon, they can go on as long as a few hours, according to Tom McLellan, an exercise physiologist with Canada's Defense Research and Development division and one of the leading experts on chemical protection equipment.
Vigorous activity -- carrying heavy gear, running, or loading and firing heavy weapons -- is possible for no more than 35 to 40 minutes while clad in a full chemical suit, according to McLellan. On the battlefield, adrenaline could extend that performance by a few minutes, but after that, he said, "they'll fall down, they won't be able to continue."
Bernard J. Fine, a former research psychologist at the Army's environmental medicine institute, said that many soldiers forced to wear such suits experience respiratory stress caused by the air resistance of mask valves.
They also can suffer from claustrophobia and a sense of isolation because they can't see a buddy's facial expression or hear his voice clearly.
On top of that, it may be hard to distinguish military officers from privates because troops in full-body chemical suits tend to look alike.
"Wearing chemical protective clothing while under enemy fire in a hot ambient temperature is a stress of the very highest order," Fine wrote in a recent article published on the Web site Globalsecurity.org.
If toxic weapons are used, U.S. forces may still be able to fight effectively if they can replenish troops frequently and quickly, some experts say. The military points out that many troops now in Iraq have trained in the Mojave Desert and are acclimated to Iraq's desert conditions by now.
But even that may not be enough, said Phillip A. Bishop, an investigator at the human performance laboratory of the University of Alabama, who has studied the experience of wearing chemical suits for nearly two decades.
"The gung-ho military attitude is that with sufficient motivation you can do anything," he said. "But you can't beat physiology and you can't beat physics."
Times staff writer Carol J. Williams, aboard the U.S. aircraft carrier Abraham Lincoln, contributed to this report.