What is the multi-gas detector's low alarm level for O2?

• A. 18.0% or below
• B. 19.5% or below
• C. 20.0% or below
• D. 21.0% or below

Answer: (B)

The main idea is understanding why oxygen deficiency is treated as a critical safety trigger. Normal air contains about 20.9–21.0% O2, so a drop to 19.5% or below is recognized as a potential hypoxia risk and will trigger a low oxygen alarm to prompt evacuation or seeking fresh air. This threshold gives workers a heads-up before oxygen levels become dangerously low, providing time to move to safer conditions. The other numbers don’t fit because 21.0% is normal air, 20.0% is still dangerously low but not the standard alarm point, and 18.0% is well into hazardous territory, which would be too late for a timely warning.