What is the operating PSI of a pressurized water extinguisher?

• A. 100 PSI
• B. 150 PSI
• C. 200 PSI
• D. 250 PSI

Answer: (A)

The main idea is the operating pressure that a stored‑pressure water extinguisher is designed to deliver water at. Water extinguishers use compressed air to push water out of the cylinder, and their design target is about 100 psi. That means when the cylinder is fully charged and at typical room temperature, the gauge reads roughly 100 psi. As you discharge the water, the pressure falls, so the gauge drops correspondingly. Temperature can affect the reading, with higher temperatures increasing the pressure and cooler temps lowering it, but the nominal operating pressure remains around 100 psi. The other numbers are too high for this type of extinguisher, which is why 100 psi is the correct choice.