Many gases invisible in normal light absorb infrared radiation (IR) to a certain degree and may therefore be made visible with the help of an IR source and a video camera aimed for IR. Two different arrangements have been used: one with the IR source as a big screen behind the observed workplace seen from the IR camera,9 and the other with the IR source dose to the IR camera with a reflector screen behind the workplace.10 The picture from the IR video camera will show the background (IR source or IR reflector) in one color and the workplace machinery and, if there, the worker as silhouettes in another color when no air contaminant is present (below the detection level). Emissions of a gas concentration high enough will be seen in the picture from the camera as a cloud spreading out from the source.
Figure 12.7 illustrates how leakage of nitrous oxide (anesthetic gas) spreads out from the patient during surgery in an operation theater.
3 О VISUALIZATION OF AIRFLOW AND CONTAMINANT DISPERSION
Applications that have been tested with good results are cases where nitrous oxide has been the air contaminant of current interest or used as a tracer gas. Other applications have been carbon disulfide in a rayon factory and styrene vapor, one of the volatile components from a surface-coating material.
The thermocamera method has the important advantage that it very effectively visualizes emission and air transport of, and workers’ exposure to, the otherwise invisible gas. By using a system that gives a presentation where different colors represent different average concentrations between the camera and the IR source, it is also possible to clearly visualize concentration gradients in the studied area. Some of the limitations are the limited number of gases that may be studied with this method and the relatively complicated work to arrange the big monochrome IR source. The price level of the equipment used is another limitation. No ready product for this method has been presented on the market, but the needed components are largely available.
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