Which reading would indicate an atmosphere is hazardous due to LEL considerations?

• A. 5% of LEL
• B. Exceeds 10% of LEL
• C. 50% of LEL
• D. 100% of LEL

Answer: (B)

Understanding LEL readings, the Lower Explosive Limit, is about knowing the concentration in air at which a flammable vapor could ignite. In many SAR and industrial safety standards, an atmosphere is considered hazardous when the gas concentration reaches or exceeds about 10% of the LEL. Crossing that threshold means the environment is within the flammable range and poses ignition risks, so protective actions are warranted. A measurement well below that, like 5% LEL, does not indicate a hazardous atmosphere by this criterion. Readings as high as 50% or 100% LEL are certainly dangerous, but the key indicator asked for is surpassing the 10% LEL threshold, which signals a hazardous atmosphere due to LEL considerations.