Sensitivity Studies of Offshore Gas Detector Networks Based on Experimental Simulations of High Pressure Gas Releases

The sensitivity of networks of flammable gas detectors to gas cloud size, high and low level placement, detector type (point and beam), alarm detection levels, response time and confirmation conditions (one or two detectors to activate an alarm) has been investigated. The network responses were simulated but based on release data from a fullscale representation of a naturally ventilated offshore process module. At larger release rates (≥5 kg s−1), detection of flammable gas clouds using a network of detectors, spaced at approximately 5 m intervals, was reliable; smaller releases were less reliably detected. The increased coverage from both high and low layers of detectors compared to a single, high level layer reduced the number of individual detectors with significantly longer than average detection times. The greater coverage of beam detectors generally resulted in improved detection rates compared to point detectors. Network detection time is not especially sensitive to the response time of the individual detectors (2-12 s), in contrast to changing the number of detectors for confirmation of an alarm. Lower alarm thresholds coupled with the use of multiple detectors alarming or detectors exceeding an alarm duration period could reliably improve detection at low release rates.