Abstract: Three chlorate candles are connected to a common conduit to which a normally open pressure switch is connected on the downstream side. The switch closes in response to a flow rate less than its predetermined minimum magnitude of oxygen from each candle flowing through the conduit. The pressure switch and one thermal switch for each candle except the last one are serially interconnected across a DC source through a resistor. When that candle first ignited is weakened in generation of oxygen, the next candle is ignited with the closure of the two serially connected switches and through the resulting heating of the associated resistor. The third candle is similarly ignited.