Transparent shielding system designed to stop flying machine debris could protect VIPs, cops, or buildings from rioters, bomb blasts, gunfire

Protecting workers from heavy debris hurtling away from high-speed rotating machinery is usually accomplished with lots of concrete, steel, and soil.

But Keith Snyder of Test Equipment Design Dept. 2955, faced with designing such a "secondary containment system" for a large high-speed centrifuge at Sandia’s Weapons Evaluation Test Lab at the Pantex Plant in Amarillo, Texas, and doing it on a limited budget, had a better idea.

Keith combined several commercially available products into a unique shielding system that is far less expensive and quicker to build than the 4-foot-thick concrete walls or underground test facilities normally relied on for machine containment.

Furthermore, the system he designed and patented has post-9/11 security applications beyond the laboratory safety uses he originally envisioned.

Safety for less

Keith’s solution is sheets of polycarbonate (clear plastic, often referred to as Lexan(r), a common brand name) glazed into frames made from Unistrut (r), commercially available pre-drilled steel bracings that, like pieces of a giant erector set, can be combined in a variety of configurations. In industrial settings, Unistrut is used to create overhead tracks for electrical conduit, racks, shelving, stairs, and other structures.

But Unistrut isn’t typically used as a barrier. Therein lies the commodity of Keith’s idea. His novel combination of struts, polycarbonate sheets, and window glazing presented some intriguing new possibilities.

For machine containment, the impact-resistant transparent sheets provide the advantage of allowing operators to safely see the machinery behind the barrier during operation, says Keith, who studied several glazing and Unistrut bracing configurations to make sure the barrier could contain whatever was flung at it by the machine.

In particular, a series of projectile impact tests conducted at the Southwest Research Institute (San Antonio, Tex.) examined how load is transferred and absorbed by the polycarbonate and bracing system when the barrier is struck by flying objects in the worst-case centrifuge mishaps.

The first such barrier was installed around the Pantex centrifuge about two years ago, after Keith made the case that it was a viable alternative to constructing a $300,000 concrete bunker around the centrifuge to stop any flying debris that escapes from the machine’s "primary containment" (the safety shielding built into the centrifuge) — or stop the centrifuge itself — in a serious accident.

"We built the first barrier in four days for about $30,000," he says.

Crowd control, VIP protection

Sept. 11 gave Keith some ideas about the braced Lexan for security applications.

Three-quarter-inch-thick Lexan is rated as bullet-proof against small arms fire, he says, so the Unistrut/polycarbonate combo would make good guard booths, for instance.

He also envisions see-through, modular, easy-to-install barriers for public gatherings to shield people from bomb blast shrapnel, protection for important functionaries who might be targets of assassins or terrorist small-arms fire during public appearances, and crowd-control walls to keep police safe and separate from rioting mobs.

More testing needs to be conducted to prove the validity of the barrier system for some security applications, he says. In particular, little data exists regarding lower-velocity impacts, such as from grenade shrapnel or objects hurled in riot situations.

Sandia recently received a US patent on the modular shield system for both machine-containment and security applications. Keith says he’d be interested in sharing the shield design and performing testing to release this system for public use, should the need arise.

More about the project is available at http://www.sandia.gov/security/Security_Barrier.