Optical sensors are placed around a section of ductwork, usually three at equidistant points. When armed, the system actively monitors a process, calibrated to identify a dangerous spark which has the potential to cause a fire or explosion in the protected process. This signal is sent to a programmable controller which activates fast-acting protection devices. These normally take the form of fast-acting valves to spray water through nozzles, extinguishing the spark as it travels down the pipe, before it enters the protected vessel. It can also be used to activate other protection devices, e.g. Quick-sliding Gate Valves, Explosion Extinguishing Barriers, Explosion Suppression Systems. This method has been critical in preventing explosions in dust collectors and other vessels.