Introduction to Gas Detection - Oliver IGD - #2

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Introduction Gas monitoring is widely used to detect the presence of a gas, which may cause a hazard,or the absence of a desirable gas. Gas monitoring is broadly split into three categories. ? Combustible gases and vapours. ? Toxic gases ? A wide range of gases can form a combustible mixture with air. Modern combustible gasdetectors are designed to detect for the presence of a build up of a combustible gas longbefore it presents a hazard to personnel or plant and equipment. Combustible gases canbe normally present due to a range of industrial or domestic processes. Oxygen deficiency or excess Combustible gases and vapours. ? Petrochemical process industries ? Gas pipelines ? Gas pumping stations ? Gas processing ? Gas Storage ? Gas Bottling ? Heating plant ? Battery charging stations ? Boiler plant ? Engine plant ? Power generation ? Gas turbines ? Landfill sites ? Bio gas generatorsFor a gas to burn in air its concentration in air must fall within certain well-defined limits. Ifthe concentration is too small then it cannot sustain a flame and will not ignite. This low limit for combustion is termed the L ower E xplosive L imit. Similarly if the concentration istoo high then there will be insufficient oxygen for the gas to combine with for combustion.This upper limit is termed the U pper E xplosive L imit. In each case over many years a wide range of gases have been characterised and theirlimits documented. Some of the more commonly encountered gases and vapours are