OLD DOG, NEW NOSE
“Take the example of water. Water has a vapor pressure of one atmosphere at 212 degrees Fahrenheit. Tat’s where it boils. Tat’s [a vapor pressure of] 14.7 pounds per square inch at sea level. At room temperature,” he continued, “it’s got about a tenth of that.” Harden said that an explosive like ammonium nitrate
“has essentially no vapor pressure at ambient temperature. We have to collect a sample on a swab, then we have to heat it up and drive it into the JCAD.”
PROTOTYPE FIELDED SOON
A member of the Utah National Guard’s 85th Weapons of Mass Destruction Civil Support Team uses a JCAD to check for chemical agent leaks during Vigilant Guard, a regional earthquake response exercise held Nov. 4, 2014, at U.S. Army Dugway Proving Ground, UT. The ATO program for JCAD CED is in the applied-prototype design phase, with plans to have a working prototype in early 2015. (Photo courtesy of Utah National Guard Public Affairs)
Tat’s why in the second, current, phase of the JCAD Chemical Explosive Detec- tor (JCAD CED), “we’ve been working with Smiths Detection to add a heated swab so that you could pick up material off a surface, or swab a suspected device, and then place that swab, like a small Q-tip, toward the inlet of the detector and then very rapidly heat it up so we generate enough vapor for it to be pre- sented for the detector,” Fountain said.
Te ATO ran from 2010 to 2012. “We are continuing to work and expand technolo- gies that were developed as part of that effort,” Fountain said. “We were given funding by the Army to look for novel ways to detect homemade explosives and [military-grade] explosives as part of the counter-IED fight. And so this is one of the efforts that we started to just see if we could take an existing chemical war- fare agent detector, JCAD, and, without any modifications to the hardware, see whether we could actually detect any explosives with it.”
VAPOR PRESSURE For the most part, CWAs have a high vapor pressure. Most explosives, on the other hand, are solid and have a low vapor
156 Army AL&T Magazine
pressure. It takes a lot of energy “for a molecule [with a low vapor pressure] to go from the condensed phase, whether it be a solid or liquid, into the vapor phase,” Fountain said. At ambient temperature, solids have very low vapor pressure and must be heated to get a sample of vapor.
“It’s not that there is no vapor present,” Fountain continued. “It’s just that it’s in such low quantities that it’s very chal- lenging to detect above the background.”
“Vapor pressure is basically how much gas you could get off a solid or a liq- uid at a particular temperature,” said Dr. Charles S. “Steve” Harden, who provides contract support to ECBC’s Point Detection Branch for Leidos, and whose doctorate is in chemical physics.
January–March 2015
SHARPENING RESULTS To help the JCAD CED detect explo- sives more readily and more accurately, the team is also adding two on-demand vapors, a dopant and a calibrant, which are two ways of refining results. It’s “been known for a long time,” Fountain said, that having a chloride ion present “just makes the explosive a little bit easier to detect. One of the things that we’ve been working with is adding this dopant [the chloride ion] to assist the formation of ions and make them more reproducible so it can be easier to detect [the explosive] with the system.”
Te calibrant, Fountain said, makes detection more reliable. “When you’re just looking for two or three chemical warfare agents, you don’t have to be as precise on your detection windows. So if an ion arrives at a certain time, plus or minus, within a given percent, you can
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