Oxygen-rich air with a level over 23.5% creates a fire hazard because it supports combustion more readily.

• A. Over 23.5%
• B. Over 19.5%
• C. Over 21%
• D. Over 25%

Answer: (A)

When oxygen levels in the air rise, combustion becomes much easier. More oxygen means fuels ignite more readily, flames can burn hotter, and ignition sources become more dangerous. Normal ambient air is about 21% oxygen, so any level above this is already a higher risk, with noticeable hazards increasing as it goes up.

The statement specifically identifies a level over 23.5% as the point where the fire hazard becomes significant. That exact threshold is what the correct choice reflects, because it matches the idea that oxygen enrichment above about 23.5% increases the likelihood and severity of ignition. The other options either fall below normal air or imply different thresholds than the one stated, so they don’t match the described hazard level.