The Selas blowout is basically a directed-flow release device combined with a check valve. It includes the check valve (A), rupture disc (B), electrical switch (C), and a flame arresting screen (D).

In normal operation, the combustible fuel/air mixture passes freely through the blowout. In the event of flashback, the increase in back pressure will cause the check valve to close and momentarily interrupt the flow of premixed gases. The pressure buildup then shatters the rupture disc thus releasing the flashback pressure and hot gases from the pipe via a vent to a safe area. (Suitable piping is required to conduct the hot gases and shattered disc material to a safe location). Rupture of the disc automatically trips the electrical switch which can be employed to command such functions as shutting off the fuel supply or sounding an alarm. The flame arresting screen delays the flame from progressing until the fuel supply is interrupted.