In NFPA 22, what is the maximum allowed difference between the tank water level and the designated fire service level?

In NFPA 22, what is the maximum allowed difference between the tank water level and the designated fire service level?

• A. 2 Inches
• B. 4 Inches
• C. 6 Inches
• D. 8 Inches

Answer: (B)

NFPA 22 requires the water surface in a tank to stay within a small tolerance of the designated fire service level so the fire protection system has a reliable, known water depth when it’s needed. The tolerance is four inches because that amount accounts for measurement and gauge variations, float and indicator inaccuracies, and normal changes in water level due to filling, settling, or temperature effects, while still ensuring there's enough water stock for a fire event. If the level differed by more than this, the pump might lose prime or cavitate, or the system could run out of water at the critical moment. That’s why four inches is the maximum allowed difference.

NFPA 22 requires the water surface in a tank to stay within a small tolerance of the designated fire service level so the fire protection system has a reliable, known water depth when it’s needed. The tolerance is four inches because that amount accounts for measurement and gauge variations, float and indicator inaccuracies, and normal changes in water level due to filling, settling, or temperature effects, while still ensuring there's enough water stock for a fire event. If the level differed by more than this, the pump might lose prime or cavitate, or the system could run out of water at the critical moment. That’s why four inches is the maximum allowed difference.