Abstract: A safety system (10) for a materials handling device, for example fork lift truck, conveyor, comprises a sensing head (11) linked to a pressurization control unit (12). The sensing head (11) monitors the level of explosive vapors in proximity to the device relative to low explosive level (LEL). When a level of explosive vapors of below 25% LEL are detected, the pressurization control unit (12) maintains the supply of an inert gas for a supply (13) to at least one sealed enclosure which encloses any hazardous components in the device at substantially atmospheric pressure. When a level of explosive vapors above 25% LEL is detected, the pressurization control device (12) is operable to increase the supply of inert gas to the enclosure (14) to being the pressure in the enclosure (14) to greater than atmospheric pressure.