What is the rating of the frangible burst disc in the valve?

• A. 6000 psi
• B. 7500 psi
• C. 5000 psi
• D. 9000 psi

Answer: (B)

The frangible burst disc acts as a one‑time high‑pressure safety release in the SCBA valve. It is built to stay intact under normal operating pressures but to fracture at a specific high pressure to vent gas and prevent the cylinder from over-pressurizing. A rating of seven thousand five hundred psi provides a safe margin above the cylinder’s working pressure (which is much lower in typical use), so the system operates normally during routine use, yet will vent if pressure spikes due to heat, blockage, or other faults. Once the disc ruptures, the valve can no longer seal properly and the cylinder is considered unsafe to reuse, requiring removal from service. The seven-thousand-five-hundred psi rating is chosen to balance reliable operation with effective protection against catastrophic failure. Lower ratings would rupture too early, and higher ratings might not relieve pressure in a dangerous overpressure situation.