Attributes . 10% LEL, 50% LEL, 100% LEL, Low alarm 19.5% O2, High alarm 23.5% O2, Over alarm 40.0% O2, 1st alarm 10 ppm H2S, 2nd alarm 30 ppm H2S, TWA alarm 10 ppm H2S, STEL alarm 15 ppm H2S, Over alarm 100 ppm H2S, 1st alarm 25 ppm CO, 2nd alarm 50 ppm CO, TWA alarm 25 ppm CO, STEL alarm 200 ppm CO, Over alarm 500 ppm CO . Names