On a QRAE 4-gas, what is the low oxygen alarm setting?

On a QRAE 4-gas, what is the low oxygen alarm setting?

• A. 18.0%
• B. 19.5%
• C. 21.0%
• D. 23.0%

Answer: (B)

The key idea is understanding the standard threshold used for triggering a low-oxygen alert. Normal air contains about 20.9% oxygen, so safety alarms are set a bit below that to warn workers before oxygen levels become dangerous. A low-O2 alarm around 19.5% is widely used because it provides a timely alert for potential hypoxia while allowing some margin for sensor drift and measurement variability. On a QRAE 4-gas, this 19.5% setting is the typical low-oxygen alarm, which is why that choice is the correct one. The other values either sit near normal air (21.0%), are too low to provide early warning (18.0%), or correspond to a high-oxygen condition (23.0%), not the low-oxygen alert.

The key idea is understanding the standard threshold used for triggering a low-oxygen alert. Normal air contains about 20.9% oxygen, so safety alarms are set a bit below that to warn workers before oxygen levels become dangerous. A low-O2 alarm around 19.5% is widely used because it provides a timely alert for potential hypoxia while allowing some margin for sensor drift and measurement variability. On a QRAE 4-gas, this 19.5% setting is the typical low-oxygen alarm, which is why that choice is the correct one. The other values either sit near normal air (21.0%), are too low to provide early warning (18.0%), or correspond to a high-oxygen condition (23.0%), not the low-oxygen alert.