Evaluation of Flammable Gas Detector Networks Based on Experimental Simulations of Offshore, High Pressure Gas Releases

Data from detailed experimental measurements of the dispersion of natural gas following high pressure releases in a naturally ventilated, simulated offshore process module were used to examine how flammable gas detector networks would respond to the releases. A network of gas detectors was simulated, incorporating detector alarm levels and response times, based on current industry practice; the response of this network to the gas releases was evaluated using various criteria. The response times of the networks were also optimized by altering the number, location and type of gas detectors used. Infrared point detectors on a 5 m grid successfully detected all releases before a 5 m diameter explosive cloud formed; catalytic detectors failed to achieve this. Examination of infrared beam detector performance indicated that due to wider coverage and faster response time they could achieve shorter detection times with fewer detectors than infrared point detectors. While large mass flow rate releases were detected, the time available before formation of significant explosive clouds was very short. Small mass flow rate releases were hard to detect, even when the total amount released became large. Well-placed detectors can improve the performance of a detection system and emphasizes the need for understanding of gas dispersion, ventilation and knowledge of the processes being undertaken in a module and their layout when deciding detector placement.