This study determines safety hazards associated with using a 300-mW 785-nm near-IR Raman laser for sample analysis. Most safety concerns are associated with excessive sample heating resulting from sample illumination. Thermography experiments were designed to quantitatively assess which visible surface colors heat most when exposed to the Raman laser. Temperatures achieved after illuminating 216 color patches with the unfocussed laser are presented. Figures contained in this report allow a field agent to rapidly determine the thermal hazards associated with Raman analysis of unknown colored samples. Dark colors tended to heat the most when exposed to the Raman laser. Studies were also conducted with a flammable organic solvent mixed with a near-IR absorbing dye to evaluate the magnitude of solution heating. Heating was minimal and Raman analysis was not considered a likely ignition hazard. The next series of experiments examined the tendency of propellants and military explosives, as well as mixtures of these explosives with IR-opaque dyes or matrix materials, to deflagrate upon illumination. All neat military explosives studied and most mixtures could be analyzed safely; however, an occasional mixture exhibited self-sustained deflagration, emphasizing safety hazards exist. Safety protocols include assessing the thermal consequences of sample analysis by referencing the thermography studies outlined above as well as minimizing the amount of sample analyzed. Several neat shock-sensitive explosives were also examined to test whether detonation could be induced by laser exposure. Black nitrogen triiodide consistently detonated, whereas colorless trinitroglycerin did not. Finally, a study was conducted to define the ignition sensitivity of various gunpowders (smokeless, black and Pyrodex powders) toward the Raman laser. All gunpowders deflagrated when illuminated. Smokeless powders were found to be the most sensitive toward laser-induced ignition.
Revised: November 10, 2005 |
Published: July 5, 2002