In confined space terminology, what defines a breathing zone?

• A. The space immediately surrounding your feet.
• B. The area 500 mm forward of your head.
• C. The area 300 mm forward of your head.
• D. The entire interior of the space.

Answer: (C)

The breathing zone is the air you actually inhale, which is the air in front of your face. In confined-space work, this is defined as roughly 300 mm (about 12 inches) forward of your head. This defines the region where contaminants can directly enter your lungs, so monitoring, ventilation, and hazard controls are focused there.

Why this fits best: air around your feet isn’t what you breathe, and the entire interior isn’t the path your inhaled air takes. A distance of 500 mm forward is farther than the air you typically draw in, so it wouldn’t accurately represent what you breathe. The 300 mm forward rule matches the real inhalation zone, making it the correct choice.