Industry uses lasers to make precision cuts and welds. Surgeons use them to repair delicate tissue. Soon, homeland security personnel may be using lasers to decontaminate sites of chemical attack.
Researchers at the Idaho National Laboratory have come up with a novel way to decontaminate difficult-to-clean material, such as porous cement or brick surfaces.
Getting toxic contaminants off these surfaces with conventional cleaning methods is difficult, since the toxins leach into the smallest cracks and holes. Conventional cleaning techniques tend to rely on other chemicals, like bleaches, which, while not toxic themselves, are corrosive and can damage surfaces. The INL scientists have found a safe way to use laser power to decontaminate surfaces using ambient water found in porous building material.
Basically, what happens is, the laser power and heat pulverizes toxic chemical compounds. The heat also flashes ambient water into steam, which carries the contaminants back to the surface for removal by an integrated vacuum system or other means.
“It’s a kind of laser steam-cleaning,” said INL chemist Bob Fox.
Fox has been studying decontamination techniques for nearly a decade, including how to remediate radiological incidents. Cleanup after a radiological event such as a dirty bomb would probably require decontaminating any buildings, roads and other infrastructure exposed to radioactivity. Performing the cleanup quickly and effectively would be vital to minimizing disruptions to commerce and community.
In a series of tests conducted at the Army’s Aberdeen Proving Ground in Maryland, INL researchers have used ultraviolet wavelength lasers to scrub surfaces clean of sulfur mustard gas and the nerve agent VX. The tests have been successful even on complex porous surfaces like concrete.
Fox and colleagues found that lasers degrade compounds like VX in two ways: photochemically and photothermally.
In photochemical decomposition, high-energy laser photons blast chemical bonds apart, essentially annihilating the toxic agent. In photothermal decomposition, photons heat up the target surface enough to accelerate the natural degradation processes of the toxic chemical compounds. In some cases, the heat is intense enough to cause the agent molecules to fall apart.
One of the problems of tampering with the chemical degradation processes is sometimes the byproducts of chemical degradation themselves can be harmful. But the INL laser technique appears to operate without this result.
“The lasers are showing neutralization of the agent without generation of dangerous byproducts,” Fox said.