Distributed Gas Detection System work by having a number of gas detection sensors placed around the fuel storage tank.
The sensors are continually feeding back gas level information to a central processor that is comparing all the measurements.
In the event of a gas measurement being substantially higher than the others, an alarm is raised. This method of detection can be constructed using off the shelf components.
Alternatively, there are a number of suppliers that provide this type of system off the shelf. Problems associated with such systems include poisoning of catalytic detectors and the fact they can be affected by weather and, particularly, moisture mist on some detections systems.