You are designing a strobe visual notification system for a fire alarm system. You have a hallway that is 4.6 m (15 ft) wide and 100 m (328 ft) long. How many strobes should be placed in the hallway?

One strobe cannot cover a 328 ft corridor while maintaining the 100 ft maximum spacing interval required by NFPA 72 for corridors up to 20 ft wide.

Two strobes positioned to meet dead-end proximity rules would be spaced approximately 300 ft apart, far exceeding the 100 ft maximum interval required by NFPA 72.

Three strobes in a 328 ft corridor would result in spacing of approximately 164 ft between devices, exceeding the 100 ft maximum spacing allowed by NFPA 72.

Per NFPA 72 Section 18.5.5.4, in corridors not exceeding 20 ft wide, visual notification appliances must be spaced no more than 100 ft apart, with the first strobe placed within 15 ft of each dead-end wall. For a 328 ft corridor, strobes at approximately 15 ft, 115 ft, 215 ft, and 315 ft satisfy both the 100 ft maximum spacing rule and the 15 ft dead-end proximity rule on both ends. Placing only 3 strobes would leave intervals exceeding 100 ft, directly violating NFPA 72.

Five strobes exceed the minimum required to satisfy NFPA 72 spacing rules for this corridor length; four strobes precisely meet all spacing and dead-end proximity requirements.