The oxygen level in a confined space should be at least _____ percent by volume.

The oxygen level in a confined space should be at least _____ percent by volume.

• A. 20.9
• B. 18.0
• C. 19.5
• D. 21.0

Answer: (C)

The main safety rule here is that the atmosphere in a confined space must have enough oxygen for safe breathing. The minimum acceptable oxygen level is 19.5 percent by volume. Normal air is about 20.9–21.0 percent, but if oxygen falls to 19.5 percent or lower, risk of hypoxia increases and a worker can become dizzy, confused, or lose consciousness. That’s why safety protocols require atmospheric testing and, if needed, ventilation to ensure the space is at least 19.5% oxygen before entry (and typically kept within a safe range around that level). The other numbers are either about normal air or too low to be considered safe.

The main safety rule here is that the atmosphere in a confined space must have enough oxygen for safe breathing. The minimum acceptable oxygen level is 19.5 percent by volume. Normal air is about 20.9–21.0 percent, but if oxygen falls to 19.5 percent or lower, risk of hypoxia increases and a worker can become dizzy, confused, or lose consciousness. That’s why safety protocols require atmospheric testing and, if needed, ventilation to ensure the space is at least 19.5% oxygen before entry (and typically kept within a safe range around that level). The other numbers are either about normal air or too low to be considered safe.