“Toxic gas detectors are commonly used throughout the workplace to warn of potentially harmful exposure to personnel and dangerous gas leaks; they play a valuable role in risk mitigation. Gas detection constitutes an important layer of protection in process facilities. They are also employed in a domestic environment, principally for the detection of carbon monoxide.
Inside plant, gas detectors are important to detect escapes of flammable or toxic cloud and to trigger mitigative devices such as water curtain or deluge system to protect work force and equipment and to prevent potential domino effects.
While effective technology exists for gas detection, placement of gas detectors is especially difficult due to the large number of variables that influence the risk associated with gas leaks; these include leak conditions, fluid properties and dispersion characteristics, process equipment geometry, detection equipment, and environmental factors.
Modeling of a chemical release is in general divided in two parts. First, “source modeling” takes into consideration characteristics of the mode of release such as type and size of rupture and geometric configuration of the container to predict the initial velocity and thermodynamic characteristics of the released pollutant. On the other hand, the atmospheric transport of the chemical cloud is treated as part of “dispersion modeling”, where atmospheric conditions, density of the cloud, and characteristics of the terrain where the dispersion occurs are utilized to predict the concentrations within the cloud as a function of distance and time.
A special problem in predicting dispersion is that many chemicals disperse as heavy gases. Heavy toxic and flammable gases are particularly hazardous because their properties of staying long near the ground and in low-wind speed condition diluting slowly.”
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