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Infrared thermography identifies laser ignition thresholds.

Monaghan-WD; Dubaniewicz-TH Jr.
Infrared News Break 2000 Feb; 15(Feb):1-2
The National Institute for Occupational Safety and Health (NIOSH) Pittsburgh Research Laboratory (PRL) are conducting research to provide a scientific basis for developing appropriate safety guidelines for optical equipment in the presence of flammables to determine laser ignition thresholds for methane-air mixtures and/or coal dust. Researchers from NIOSH-PRL are working with safety standards committees such as: The International Society for Measurement and Control (ISA) and the International Electrotechnical Committee to develop safety recommendations for lasers in hazardous locations. In phase 1 of the "Laser Safety for Hazardous Locations" project, infrared thermographs recorded temperatures of iron oxide particles on optical fiber tips heated by laser powers that previously have produced methane-air ignition. About 120 experiments were conducted to determine laser-heated target temperatures at and near laser powers required to ignite methane-air, under several different test conditions producing temperatures in the range of 1300 to 1500 Celsius. The research is part of a project to recommend safe power limits for lasers used in coal mines. In one phase of the project, researchers used a thermal imaging system which measured infrared radiation at wavelengths of 3.6 to 5um, and was calibrated up to 1500'C by the manufacturer. A 30/BO-mm close-up lens allowed very high spatial resolution. Prior to observations of the optical fibers, the temperature calibration and spatial resolution of the thermal imaging system were confirmed by using small apertures placed in front of a blackbody source. Temperature measurements were within manufacturer's specifications down to the smallest aperture, a' 340-um hole drilled through a thin metal sheet. In phase II of the project the infrared system recorded time lapse thermographic images of a laser beam incident on a coal dust layer. The thermal imaging system measures infrared radiation at wavelengths from 3.6 to 5 micrometers (micro m). The manufacturer calibrated the system to accurately measure temperatures up to 1500 Celsius (Degrees C) for the high temperature tests. The calibration of the system was confirmed here at PRL with a blackbody source. Of particular interest in our research is the use of this system to provide continuous quantitative analysis of thenmal runaway phenomenon. The system is used to observe spatial and temporal temperature variations of a coal hot spot.
Lasers; Ignitability; Ignition-point; Ignition-sources; Ignition-systems; Methanes; Coal-dust; Laboratory-testing; Statistical-analysis
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Infrared News Break