"flame arrestor" means a device to prevent the passage of flame, complying with all relevant requirements of this Schedule. Its flame arresting mechanism is based on the principle of quenching;
"flame screen" means a device utilizing wire mesh to prevent the passage of unconfined flames, complying with all relevant requirements of this Schedule;
"flame speed" means the speed at which a flame propagates along a pipe or other system;
"flash-back" means the transmission of a flame through a device;
"high velocity vent" means a device to prevent the passage of flame consisting of a mechanical valve which adjusts the opening available for flow in accordance with the pressure at the inlet of the valve in such a way that the efflux velocity cannot be less than 30 metres per second and complying with all relevant requirements of this Schedule;
"pressure/vacuum valve" means a device designed to maintain pressure and vacuum in a closed container with preset limits.
