Open path IR gas detectors are a mainstay in the oil and gas industry. They are used in a variety of instances to identify
gas accumulations or monitor gas cloud migrations. In offshore installations, open path optical gas detectors are used to
monitor drilling and production operations, crude oil separation, compression, and exhaust and ventilation systems.
Because they can monitor a perimeter or fence line, they are ideally suited for detecting gas in open facilities, where
point gas detectors would be difficult or expensive to deploy.
Despite their widespread use, open path optical gas detectors are rarely employed to detect low level concentrations of
combustible gases. Standard models are typically set to alarm at 50% LEL-m (50% LEL extended over one meter),
providing sufficiently early warning when gas accumulations occur. Nevertheless, in cases in which a combustible gas is
diluted quickly, such as ventilation exhaust ducting, it may be necessary to set the detector to alarm at the lowest
predictable level. Further, interest in low level infrared gas detection has been growing as gases such as CH4 and CO2 are
The present paper describes a mid-wave infrared (MWIR) open path system designed to detect combustible and carbon
dioxide gas leaks in the parts-per-million-meter (ppm-m or mg/cm2). The detector has been installed in offshore
platforms and large onshore facilities to detect a variety of flammable gases and vapors. Advantages and limitations of
the system are presented. False alarm immunity and resilience to atmospheric interferences are also discussed.