PUEBLO, Colorado—On the dry, windswept plains of southeastern Colorado, a military checkpoint protects a vast field of igloos built with corrugated steel, covered with a thick layer of Earth, and fitted with thick, blast-resistant doors. The walls of the igloos keep the interior a consistent 51 degrees Fahrenheit whether it's in the heat of summer or the depths of winter, and the high-altitude air has little enough water in it that corrosion-causing moisture is an afterthought.

These mounds are carefully spaced to prevent an explosion in one igloo from triggering explosions in neighboring igloos. That's because inside, the US military stores a stockpile of 780,000 unused WWII-era munitions, filled with dangerous and deadly viscous sulfur mustard agent. This stockpile of chemical weapons was shipped to these igloos in the 1950s. They have been carefully guarded since then.

Not all chemical weapons in the US were so carefully handled. Between 1967 and 1970, the US military disposed of "thousands of tons" of chemical weapons by simply dumping them in the ocean as part of Operation CHASE (Cut Holes And Sink 'Em), according to the Centers for Disease Control and Prevention. In fact, the military dumped 16,000 bombs, each containing 73 pounds of chemical agent, in the ocean at a site five miles south of Pearl Harbor after World War II. In 2010, research teams decided not to move the sunken munitions because moving the bombs would be more risky than leaving them where they are.

In 1972, Congress outlawed dumping chemical weapons in the ocean, and in 1997, the US became a signatory to the Chemical Weapons Convention, an international treaty to eliminate chemical weapons stockpiles. Without the option of simply dumping weaponized chemicals into the sea, incineration or neutralization was the choice on the table. Destruction plants were built around the country to eliminate stockpiles. After years of planning, construction of the Pueblo Chemical Agent-Destruction Pilot Plant (PCAPP) began.

After numerous and extensive delays, the plant was finally finished in the summer of 2016. Since then, the plant has been slowly ramping up destruction of the chemical-containing munitions that had lain dormant for so long in Pueblo’s prairie igloos, which are part of the Pueblo Chemical Depot.

Bechtel, the company contracted by the US military to oversee and develop the plant, recently offered Ars a tour of the training facility that the plant uses to get its employees up to speed on this destruction process. Going to the pilot plant itself, Bechtel said, would be too risky. Still, the training facility, which sits in a nondescript warehouse park east of Pueblo, houses much of the same equipment you’d find in the real plant. There's just a lesser risk of exposing an untrained journalist to mustard agent, of course.

A word about sulfur mustard

Coming in contact with mustard agent, otherwise known as sulfur mustard, is extremely bad, despite the fact that it's not immediately fatal in most cases. Although you might not experience symptoms for up to 24 hours, once you do, your skin will start itching and burning intensely until large blisters filled with yellow fluid start forming. If your eyes are exposed, they will become swollen and sore, and exposure could induce blindness for up to 10 days. If you breathe the sulfur mustard in, your lungs could blister and fill with fluid. While mild exposure can be treated, leading only to first and second degree burns, heavy exposure can cause disfiguring third degree burns. And mustard agent burns heal more slowly than other burns, leading to increased risk of sepsis.

If a large portion of your body surface area is exposed and you don't get adequate medical treatment, you could die... in a process that can take days or weeks. On top of all that: even if you only have mild exposure, sulfur mustard is carcinogenic and can lead to increased risk of cancer later in life. (Somehow it hasn't always been such a reviled substance: decades ago doctors prescribed sulfur mustard as a treatment for psoriasis.)

This chemical, sometimes deployed as a gas and other times deployed as a liquid, was initially used as a weapon by the Germans during WWI. British and Canadian soldiers fighting in Belgium were the first to experience the horrors associated with exposure, and the British government quickly went about developing its own chemicals. Use of chemical weapons in warfare was internationally outlawed in 1925 per the Geneva Protocol, but the US built its own stockpiles of mustard-agent-filled shells through WWII. Although by most accounts the US never deployed any of its own sulfur mustard against the axis powers, it did expose 60,000 of its own troops to chemical agents in secret experiments that singled out white, black, Japanese, and Puerto Rican soldiers. In the '90s, military documents were unearthed that the US had planned a poison gas attack against Japan that could have killed five million people.

Robots tread where man dare not

The training facility for the Pueblo Chemical Agent Destruction Pilot Plant is 17 miles west of the actual plant. It houses working machinery that prospective employees get to practice on, as well as classrooms where dozens upon dozens of classes are taught before employees come in contact with munitions or machinery. Employees tend to be people with chemical industry experience, power plant and gas transmission station workers, veterans, or people who’ve worked on military bases before.

Plant support specialist Tom Bailey walked Ars through the process of destroying the chemical munitions. From the get-go, employees are largely remote to the disassembly process. While the projectiles are coming apart, these individuals direct robots, automatic forklifts, and other machinery from a separate building or while shielded by 24-inch-thick blast walls and guided by fiber-optically linked video cameras. In the training facility, instructors have set up a fence around the disassembly machinery to give employees a physical reminder of the boundaries they’ll have to work around.

The employees run through the process using empty munitions casings, clean of any explosives or chemicals. At Pueblo, the plant is only concerned with destroying 155mm and 105mm projectiles filled with HD (a type of sulfur mustard) and some 4.2-inch mortar bombs. That lack of variety is helpful because it reduces how versatile the site needs to be. A weapons destruction plant in Kentucky, for example, destroys many different types of weapons, including weapons that contain sarin and other nerve agents. The Kentucky plant has fewer weapons to destroy, but the variety makes everything slower.

Megan Geuss

Megan Geuss

Megan Geuss

Megan Geuss

Megan Geuss

To understand how the machinery at Pueblo destroys the chemical weapons, employees of the plant need to know how the munitions were constructed. Yes, essentially the destruction process is a finely tuned bit of reverse manufacturing. Although the Pueblo Chemical Depot has long had the ability to simply explode and incinerate these chemical weapons on site in what's called a "static detonation chamber," the incinerator can only destroy about six rounds a day. When you're up against a stockpile of 780,000, that just wouldn’t do.

Instead, the incinerator is reserved for munitions that fail to meet the criteria for a more careful destruction at the Chemical Agent-Destruction Pilot Plant, like if a projectile looks like it won’t hold up on the main machinery or if the machinery is having trouble removing some of the chemicals inside a projectile. By contrast, each of the three disassembly lines in the pilot plant can theoretically disassemble 60 rounds an hour, although that decreases to an average of about 42 to 46 rounds an hour in practice when the facility is entirely up and running.

Bringing out a cross-section model of a 155mm projectile, Bailey started methodically explaining the components. Munition this heavy would usually be fired out of a large artillery piece, like a Howitzer gun. The shell of the munition would have been cold-cast in hopes that when it exploded over enemy lines, it would fracture and deploy the chemical agent. ("People like to call it mustard gas, but it’s not a gas, it's a liquid," Bailey explained. "It’s a heavy viscous liquid, and the object of this is for it to splash on you. It’s not aerosolized.")

After casting the casing, manufacturers would fill it to a point with the heavy viscous chemical agent (a type of sulfur mustard classified as "HD" by the military) before hydraulically pressing a burster well into the shell. Then the explosive burster material would be fit into the burster well, and a fuse well cup would top it all off. The fuse well cup was molded such that you could screw a lifting lug into the top of the projectile for transportation purposes. “First thing the army does to get ready to use these is they remove the lifting lug and install a fuse in its place,” Bailey said. “By that time they’re finished handling it.”

Today, many of the munitions are already stored in pallets (some of the smaller ones require special packing). To get to the pilot plant, they're loaded onto a special truck at the storage igloo, and a driver makes the barely one-mile drive from igloo to plant in what Bailey described as a “torturous” and slow fashion.

Listing image by Megan Geuss