Combustible Gas & Oxygen Meter

Combustible Gas & Oxygen Meter

Combustible gas indicators (CGIs) measure Combustible gas indicators (CGIs) measure the concentration of a flammable vapor or the concentration of a flammable vapor or gas in air, indicating the results as a gas in air, indicating the results as a percentage of the lower explosive limit percentage of the lower explosive limit (LEL) of the calibration gas.(LEL) of the calibration gas.

Combustible Gas & Oxygen Meter

Principle of OperationPrinciple of Operation

The LEL (or LFL - lower flammable The LEL (or LFL - lower flammable limit) of a combustible gas or vapor is the limit) of a combustible gas or vapor is the minimum concentration of the material in minimum concentration of the material in air which will propagate flame on contact air which will propagate flame on contact with an ignition source.with an ignition source.

Combustible Gas & Oxygen Meter

Principle of OperationPrinciple of Operation

Above the UEL, the mixture is too "rich" to Above the UEL, the mixture is too "rich" to support combustion so ignition is not support combustion so ignition is not possible. Below the LEL there is possible. Below the LEL there is insufficient fuel to support combustion.insufficient fuel to support combustion.

Combustible Gas & Oxygen Meter Limitations &

Considerations TemperatureTemperature Oxygen LevelsOxygen Levels Interfering CoumpoundsInterfering Coumpounds

Organic LeadOrganic Lead Sulfur compoundsSulfur compounds SiliconeSilicone Acid GasesAcid Gases

Combustible Gas & Oxygen Meter Calibration is performed with calibration Calibration is performed with calibration

gas, which contains precise concentrations gas, which contains precise concentrations of several gases.of several gases.

Meter is calibrated to calibration gas for Meter is calibrated to calibration gas for LEL, therefore correction factors must be LEL, therefore correction factors must be applied when using detector on other types applied when using detector on other types of gases.of gases.

Combustible Gas & Oxygen Meter

Hot wire operation-test gas is passed over a Hot wire operation-test gas is passed over a heated wire(sometimes in the presence of a heated wire(sometimes in the presence of a catalyst). The test gas burns, changing the catalyst). The test gas burns, changing the temperature of the filament, and the temperature of the filament, and the electrical resistance of the filament is electrical resistance of the filament is measured.measured.

References Cited

NIOSH Manual of Analytical Methods NIOSH Manual of Analytical Methods (NMAM®), 4th ed.(NMAM®), 4th ed.DHHS (NIOSH) Publication 94-113 DHHS (NIOSH) Publication 94-113 (August, 1994),(August, 1994),Cassinelli, M.E. & Cassinelli, M.E. & O'Connor, P.F. (pfo1@O'Connor, P.F. (pfo1@cdccdc..govgov)), Eds., Eds.

Bibliography

DiNardi Salvatore R. (1998) DiNardi Salvatore R. (1998) The The Occupational Environment-Its Evaluation Occupational Environment-Its Evaluation and Controland Control, AIHA, Fairfax, Virginia , AIHA, Fairfax, Virginia

Goetsch David L. (1999) Goetsch David L. (1999) Occupational Occupational Safety and Health for Technologists, Safety and Health for Technologists, Engineers, and ManagersEngineers, and Managers, Prentice Hall, , Prentice Hall, Upper Saddle River, New Jersey Upper Saddle River, New Jersey