If external foreign material clogging is likely, what feature should discharge nozzles have?

• A. Frangible discs, blow-off caps, or other suitable devices that provide an unobstructed opening upon system operation and shall be located so they will not injure personnel.
• B. Discharge nozzles must be painted red.
• C. No devices are required.
• D. Discharge nozzles shall be provided with frangible discs, blow-off caps, or other suitable devices that will provide an unobstructed opening upon system operation and will be located so they will injure personnel.

Answer: (D)

When external debris that could clog the nozzle is expected, the discharge nozzles must be designed to stay open and deliver the agent reliably. Using protective devices like frangible discs or blow-off caps ensures there is an unobstructed opening at the moment of system activation—the disc breaks or the cap vents, exposing the bore so the clean agent can flow freely. At the same time, these devices and their mounting should be arranged so that their operation cannot endanger personnel during discharge. This combination—unobstructed opening plus safe placement—provides both reliable discharge and improved safety, which is why this approach is required in systems prone to foreign-material blockage.