Frustrated by the inability of the SPiTFiRE test fixture to equally disseminate chemical agent vapor over the surface of fabric samples, Dr. Aaron Rogers of Dugway Proving Ground (DPG) pondered solutions.
The SPiTFiRE (Swatch Permeation Test Fixture, Reengineered) was better than previous test fixtures developed at DPG, but wasn’t delivering the data quality the Air Force requires for the pilot stage of the Vapor Off-gassing Re-use Test (VORT).
The test will determine if chemically contaminated aircrew protective clothing off-gases fast enough to be safely worn again. A variety of fabrics, taken from actual aircrew protective clothing, will be tested. If off-gassing is safe, it will greatly reduce the distribution of new protective clothing and the money, effort, time and fuel used to get it to Airmen.
To apply chemical agent to fabric swatches equally, Project Scientist Rogers had an idea: put all 10 fabric samples in a Vapor Box that would expose all swatches to chemical agent at once.
The Vapor Box was Rogers’ brainchild but, “The whole thing was made up by (West Desert Test Center’s) Test Support Division, and (engineer) Greg Dahlstrom in particular,” Rogers said.
The engineers used a 3D printer, with resin, to create the Vapor Box with recessed slots to hold 10 swatches of fabric. Agent enters and leaves via two holes at the top of a horseshoe-shaped exposure area. After contamination, each swatch is removed and put in individual sealed cups to monitor off-gassing.
Currently, the Air Force has invested $125,000 in the VORT pilot stage, which will run another three months.
"We successfully completed the first trial with the Vapor Box setup and it worked well," said Rogers. "However, we can't draw any conclusions about utility yet, since the sample size is too small. In early or mid-April we expect to do two more trials, which will give us a better indication of Vapor Box performance."
If the pilot is successful, test trials of up to two years will follow.
“If all goes well, and the design is a success, the full test effort will be funded,” Rogers said.
The pilot stage will validate the Vapor Box in accordance with Department of Defense Instructions, Number 5000.61 (DODI 5000.61), the governing policy document for modeling and simulation.
“The use of swatches is considered a modeling system,” Rogers said. “We build the prototype Vapor Box, then validate it according to the customer’s test parameters.”
If the first Vapor Box does not work as expected, another one will be 3D printed with the changes. 3D printing is cheaper, easier, faster and lighter than fabricating with stainless steel, the standard for decades.
3D printing provides a means of rapidly generating components for a test fixture to be used in actual testing and then when validated, produced from hardened material. The process of prototyping / validation is interactive, allowing the kinks to be worked out before spending greater money on a hardened material version made of stainless steel.
“This could be the beginning of a big change in fixture development,” Rogers said. “We’re always looking for more cost effective means (to create fixtures), because funding keeps drying up more and more.”