In NFPA 13R, shadowed areas shall be permitted in the protection area of a pendant or upright sprinkler as long as the cumulative dry areas do not…

According to NFPA 13R, when dealing with obstructions to the discharge of pendant or upright sprinklers, minor "shadowed areas" are permissible. The standard explicitly allows for these dry areas under the condition that their total, or cumulative, size does not exceed a specific limit. This limit is set at 15 ft² (1.4 m²). This provision acknowledges that complete water coverage might be impeded by small, fixed obstructions without critically compromising the system's effectiveness in a low-rise residential fire scenario.

A. 5 ft² (0.46 m²): This value is incorrect and significantly more restrictive than the allowance specified in the standard for cumulative dry areas.

B. 10 ft² (0.93 m²): This is not the correct threshold; it understates the maximum cumulative dry area permitted by NFPA 13R.

C. 12 ft² (1.1 m²): This value is not specified in NFPA 13R as the maximum limit for cumulative shadowed areas.

1. NFPA 13R, Standard for the Installation of Sprinkler Systems in Low-Rise Residential Occupancies, 2022 Edition, Section 9.5.5.3.1.3.

2. SFPE, Handbook of Fire Protection Engineering, 5th Edition, Springer, New York, NY, 2016, Chapter 49, "Automatic Sprinkler Systems," Section 49.5.3.2, which discusses residential sprinkler installation standards and their specific provisions for obstructions. (DOI: https://doi.org/10.1007/978-1-4939-2562-449)