This Practice provides guidelines for the selection, design, and application of fixed gas monitoring detectors installed in process areas to detect the presence of combustible gases, oxygen, or toxic gases. This Practice addresses detectors permanently installed for ambient air monitoring (e.g., leak detection, oxygen depletion). The technologies included are catalytic bead, infrared, electrochemical, paramagnetic. This Practice does not cover portable gas monitoring equipment, process analyzers, or sampling systems. The systems used to perform data acquisition, alarming, and control action are not covered by this Practice because the solutions are diverse and can include stand-alone to advanced multisystem configurations.