Lasers Promising for Chemical Decontamination
WASHINGTON, DC, April 27, 2010 — The Department of Homeland Security (DHS) is funding research that involves using lasers to decontaminate chemical explosion sites. Because the threat of a chemical attack on US soil is a reality the DHS’s Science and Technology Directorate (S&T) is supporting chemists at Idaho National Laboratory (INL) in their search for more effective decontamination methods in the event of an attack.
Many building materials — like cement and brick — are extremely porous. Getting contaminants off surfaces like these is difficult, since they can inhabit cracks and pores. Cleaning up chemical-contaminated structures can be difficult, costly, and time-consuming. For one thing, most preferred methods employ other chemicals, like bleach solutions, which can be corrosive and aggressive to many types of surfaces.
According to Donald Bansleben, program manager in S&T’s Chemical and Biological Division, lasers could one day play a big role. “Lasers could help to scrub chemical-contaminated buildings clean and become a tool in the toolbox to speed a facility’s return to normal operations,” he said.
Water inhabits those cracks and pores too, and that’s where lasers come in. INL chemists have shown that laser pulses can flash that water into steam, carrying the contaminants back to the surface for removal by chelation or other means.
“It’s a kind of laser steam-cleaning,” said Bob Fox, an INL chemist.
A neodymium-YAG (Nd:YAG) laser will decompose VX nerve agent in this vinyl tile. Normally near-infrared, the laser turns ultraviolet as the frequency is increased. The UV light breaks the molecular bonds, decomposing the deadly nerve agent until it is just a harmless brown stain.
When INL began investigating lasers, researchers were looking for ways to dispose of radioactive contamination after a dirty bomb. Under the new S&T program, the team has been extending its work to chemical-weapon decontamination. While no terrorist has managed to deploy a dirty bomb, the same cannot be said of chemical agents.
As a new remediation technology, lasers show promise. In a series of tests still underway at the Army’s Aberdeen Proving Ground, the INL researchers have been using ultraviolet-wavelength lasers to scrub surfaces clean of sulfur mustard gas and VX, a nerve agent. The tests have proved successful so far, even on complex, porous surfaces like concrete.
Lasers can degrade weapons like VX in two ways: photochemically or photothermally. In photochemical decomposition, high-energy laser photons blast apart chemical bonds, slicing the agent into pieces. In photothermal decomposition, photons heat up the target surface enough to speed along natural degradation reactions. In some cases, the intense heat by itself can cause contaminant molecules to fall apart.
Knowing how chemical contaminants fall apart is key, because some of the elements resulting from their degradation products can themselves be hazardous. But according to Fox, the tests look good in this regard, too. “The lasers are showing neutralization of the agent without generation of dangerous byproducts,” he says.
And even if they’re not used to degrade VX or other agents, lasers could still be helpful in cleanup scenarios. Laser light could blast nasty chemicals off a wall, for example, and an integrated vacuum system could suck them up.
While using lasers to decontaminate office buildings or subway stations may sound like science fiction, Fox and his team are merely adapting an established technology. Lasers have been used in cleanup capacities for more than a decade. Dentists employ them, for example, to kill periodontal bacteria and quash mouth infections. Doctors use them to remove tattoos. And lasers have recently become a common tool to restore precious artwork.
Laser technology has other commercial applications. Some cleanup and restoration firms are already using lasers to scrub soot off building facades. And these industrial operations often use automated lasers, demonstrating that laser work can be done remotely, minimizing risks to remediation personnel responding to a chemical or radiological attack.
Fox stresses that laser decontamination is in the proof-of-principle stage, and is not an anti-terror panacea. Still, several government agencies are paying close attention as the INL team showcases the technology’s promise.
As for biological decontamination, like what was needed in the US after the 2001 anthrax attacks, Fox has not yet tested bacteria-laden surfaces. “I don’t know,” he said. “But I’m willing to shine my light on anything.”
For more information, visit: www.dhs.gov
MORE FROM PHOTONICS MEDIA