Steel and aluminum cylinders for breathing apparatus should be hydrostatically tested after each -year period.

• A. Two
• B. Three
• C. Four
• D. Five

Answer: (D)

Hydrostatic testing intervals are set to catch any hidden defects in cylinders before they fail under high pressure. For steel and aluminum cylinders used in breathing apparatus, the standard interval is five years. In the test, the cylinder is filled with water and pressurized to 1.5 times its service pressure to look for leaks, distortion, or failure. If it passes, the cylinder receives a new test date and can be used for another five years. This five-year schedule reflects the fatigue characteristics of metal cylinders and strikes a practical balance between safety and maintenance cost. Shorter intervals aren’t the accepted practice for these metal cylinders.