When is the warning condition cleared?

• A. When the H2S concentration at all detector heads is less than 60 PPM
• B. When the H2S concentration at all detector heads is less than 10 PPM
• C. When the H2S concentration at all detector heads is less than 20 PPM
• D. When the amber indicator resets

Answer: (B)

The warning clears only when every detector head reads below 10 PPM, ensuring the entire monitored area is back to a safe level. With multiple heads, you don’t want one area still above the safe limit while another has dropped below it; that would leave some exposure risk unseen. Ten PPM is the threshold used here as the point at which H2S concentrations are considered safe enough to resume normal operation. If any head remains at or above 10 PPM, the warning stays active because a hazardous condition could still exist somewhere in the coverage area. The amber indicator is a signal that the system is in warning, but the actual condition for clearing is all-head readings below 10 PPM.