It’s a balmy 68 degrees at Natick this afternoon. It may, at the same time, be 70 below zero with horizontally blown snow or 110 in the shade, depending on what’s being tested over in the Doriot. The Doriot Climatic Chambers were the centerpiece of the complex when it opened in 1954. Never again would troops be sent to the Aleutian Islands with seeping, uninsulated boots or to equatorial jungles with no mildew-proofing on their tents. Soldiers fight on their stomachs, but also on their toes and fingers and a decent night’s sleep.
These days, the snow and rain machines are rented out to L.L. Bean or Cabela’s as often as they’re used to test military outerwear. Repelling the elements is the least of what the US Army needs its uniforms to do. If possible, the army would like to dress its men and women in uniforms that protect them against all that modern warfare has to throw at them: flames, explosives, bullets, lasers, bomb-blasted dirt, blister agents, anthrax, sand fleas. They would like these same uniforms to keep soldiers cool and dry in extreme heat, to stand up to the ruthless rigors of the Army field laundry, to feel good against the skin, to look smart, and to come in under budget. It might be easier to resolve the conflicts in the Middle East.
LET US begin at Building 110, which is what everyone calls it. Officially it was christened the Ouellette[4] Thermal Test Facility, lending a flirtatious French flair to lethal explosions and disfiguring burns. The head textile technologist is a slim, classy, fiftyish woman of fine-grained good looks, dressed today in a cream-colored cable-knit wool tunic. I took her to be the Ouellette, and then she opened her mouth to speak and a hammered-flat Boston accent flew out and slammed into my ear. She is an Auerbach, Margaret Auerbach, but around 110 she’s just Peggy, or “flame goddess.”
When someone in industry thinks they’ve built a better flame-resistant fabric, a sample comes to Auerbach for testing. Some people submit swatches; others optimistically ship off whole bolts. Their hopes may be undone by a single strand of thread. “To see what our guys might be inhaling,” Auerbach heats a few centimeters of thread to around 1500 degrees Fahrenheit. The fumes produced by this are identified by gas chromatography. Flame-resistant textiles—some, anyway—work via heat-released chemicals. Auerbach needs to be sure the chemicals aren’t more dangerous than the flames themselves.
Once it’s established that the textile is nontoxic, Auerbach sets about testing its flame-stopping mettle. This is done in part with a Big Scary Laser (as the sticker on its side reads). Auerbach places a swatch in the laser’s sights. And here is the best part: To activate this laser, you push a giant red button. The beam is calibrated to deliver a scaled-down burst of energy representative of an insurgent’s bomb—a teacup IED. A sensor behind the swatch measures the heat passing through, yielding a figure for how much protection the fabric provides and what degree burn would result.
Auerbach switches on a vacuum pump that sucks the swatch tight against the sensor. This is done to approximate an explosion’s pressure wave—the dense pileup of accelerated air that can knock a person flat. More subtly, it forces clothing flush against the skin, which can heighten the heat transfer and worsen the burn. One of the winning attributes of Defender M, the textile of the current Flame Resistant Army Combat Uniform, or FR ACU (“the guys call it ‘frack you’”), is that it balloons away from the body as it burns.
The downside to Defender M has been that it tears easily. (They’re working on this.) The same thing that keeps it comfortable in hot weather also makes it weaker; it’s mostly rayon, which draws moisture but has low “wet strength.” If a garment tears open in the chaos of an explosion, now the protective thermal barrier is gone. Now you’re toast. The manufacturer throws a little Kevlar in, but it still isn’t as strong as Nomex, a fiber often used for firefighter uniforms. Nomex also has superior flame resistance: It buys you at least five seconds before your clothes ignite.
Auerbach explains that this is especially important for crews inside tanks and aircraft. “Where they can’t roll, drop, and…” She rewinds. “Drop, stop… what is it?”
“Stop, drop, and roll?”
“Thank you.”
Why not make all army uniforms out of Nomex? Poor moisture management. Not the best choice for troops running around sweating in the Middle East. And Nomex is expensive. And difficult to print with camouflage.
This is how it goes with protective textiles: Everything is a trade-off. Everything is a problem. Even the color. Darker colors reflect less heat; they absorb and transfer more of it to the skin. Auerbach goes across the lab to get a swatch of camouflage print cloth. She points to a black area. “You can see this has a pucker where it was absorbing more heat.”
“It has a what?” I heard her, but I need to hear her say pucka again. The fabulous Boston accent.
I would have guessed the military to be a fan of polyester: strong, cheap, doesn’t ignite. The problem is that it melts and, like wax and other melted items, it drips and sticks to nearby surfaces, thereby prolonging the contact time and worsening the burn. What you really don’t want to be wearing inside a burning army tank is polyester tights.[5]
To determine what degree of injury the heat would produce, Auerbach runs the reading from the sensor behind the cloth through a burn prediction model—in this case, one developed after World War II by original flame goddess Alice Stoll. Stoll did burn research for the Navy. To work out first- and second-degree burn models, she gamely volunteered the skin of her own forearm. You may excuse her for letting someone else help out with the third-degree burn curve. Anesthetized animals were recruited for this—rats, mostly, and pigs. Pig skin reflects and absorbs heat in a manner more like our own than that of any other commonly available animal. The pig as a species deserves a Purple Heart, or maybe Pink.
What Stoll learned: When flesh reaches 111 degrees Fahrenheit, it starts to burn. The Stoll burn prediction model is a sort of mathematical meat thermometer. The heat of the meat and how deeply into the skin that heat penetrates are the critical factors that determine the degree of the burn. A brief exposure to flame or high heat cooks, if anything, just the outer layer, creating a first-degree burn or, to continue our culinary analogy, lightly seared ahi tuna. A longer exposure to the same heat cooks the inner layers, too. Now you have a second- or third-degree burn, or a medium-rare steak.
Even without a flame, clothing can catch fire. The auto-ignition temperature for cotton, for instance, is around 700 degrees Fahrenheit. Exposure time is key. The heat pulse from a nuclear blast is extremely hot, but it’s traveling at the speed of light. Might it pass too quickly to ignite a man’s uniform? Natick’s early precursor, Quartermaster Research and Development, actually looked into this.
Operation Upshot-Knothole was a series of eleven experimental nuclear detonations at the Nevada Proving Grounds in the 1950s. The Upshot-Knothole scientists were mainly interested in the blastworthiness of building materials and tanks and bomb shelters, but they agreed to let the uniform guys truck over some pigs. Anesthetized Chester White swine, 111 in total, were outfitted in specially designed animal “ensembles” sewn from different fabric combinations—some flame-resistant and some not—and secured at increasing intervals from the blast.
4
Misspelled as “Uoellette” on the Natick Building Inventory, and “Oullette” on the sign outside the building. Somebody burned for that one.
5
I went on the National Electronic Injury Surveillance System to find you a figure for the number of burns caused each year by pantyhose. Alas, NEISS doesn’t break clothing injuries down by specific garment. I skimmed “thermal burns, daywear” until I ran out of patience, somewhere around the thirty-seven-year-old man who tried to iron his pants while wearing them.