Confined Spaces - Workplace Safety and Health Council

Instrument Reading in % LEL100500Figure 12: An example of sensitivity chart.Methane, Ammonia0 50 100Applied Gas or Vapour in % LELLinear respondPropane,Butane,AcetoneHexane,EthylacetateToluene,Xylene,NonaneFor confined spaces with various flammable gases present, it is recommended that the calibrationbe done using the gas that the sensor is least sensitive to so as to have a higher safety factor.Where applicable, it is important to calibrate using a target gas.In the event where the target gas is not available for calibration, it is necessary to take thecorrection factor into consideration. For example, if the instrument is calibrated to methaneand this is used to measure butane, it is important to use the correction factor provided by theinstrument manufacturer so that the reading is corrected.The given values are typical values for calibration with methane (CH 4) and are applicable to newsensors without additional filter materials. The LEL for methane in the table is 5 % by vol.NoteAs the value of the correction factor may vary slightly between meters, the mentionedvalues below are only examples. It is advisable for the user to check specifically fortheir equipment.Calibration GasX-am 3000,Pac Ex 2Methane Propane PentaneAcetone 2.20 1.16 1.00Ammonia 0.60 0.32 0.27Benzene 2.50 1.32 1.14Butadiene - 1,3 2.00 1.05 0.91n-Butane 2.00 1.05 0.91n-Butylalcohol 4.50 2.37 2.052-Butanone 2.60 1.37 1.18n-Butylacetate 3.90 2.05 1.77Cyclohexane 2.50 1.32 1.14Cyclopentane 2.50 1.32 1.14Diethylether 2.30 1.21 1.05Acetic acid 2.50 1.32 1.14Ethane 1.40 0.74 0.64Ethylalcohol 1.70 0.89 0.77Ethene 1.50 0.79 0.68Ethine 1.20 0.63 0.55Ethylacetate 2.60 1.37 1.18n-Heptane 3.00 1.58 1.36n-Hexane 2.30 1.21 1.05Carbon monoxide 1.20 0.63 0.55Methane 1.00 0.53 0.45Methylalcohol 1.50 0.79 0.68n-Nonane 4.00 2.11 1.82n-Octane 2.90 1.53 1.32n-Pentane 2.20 1.16 1.00Propane 1.90 1.00 0.86i-Propylalcohol 2.70 1.42 1.23n-Propylalcohol 2.70 1.42 1.23Propene 1.80 0.95 0.821,2-Propyleneoxide 2.10 1.11 0.95Toluene 2.50 1.32 1.1438 Hydrogen 1.20 0.63 0.5539o-Xylene 3.50 1.84 1.59