According to NFPA 13D, Standard for the Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes, the hydraulic design is based on the most demanding scenario. The standard requires the system to provide a flow of not less than 18 gpm to any single operating sprinkler AND not less than 13 gpm per sprinkler to the two most hydraulically demanding sprinklers.

The two-sprinkler scenario requires a total flow of 26 gpm (2 sprinklers × 13 gpm/sprinkler), which is greater than the 18 gpm required for the single-sprinkler scenario. Therefore, the two-sprinkler calculation is the more demanding condition and governs the hydraulic design to ensure the water supply is adequate. The ceiling height and characteristics described do not alter this fundamental requirement.

A. 1: While a single sprinkler flow rate is a required criterion, the two-sprinkler calculation demands a higher total water flow and therefore governs the system's design.

C. 5: This number of sprinklers is not a design requirement in NFPA 13D. It is more characteristic of calculations for systems designed under NFPA 13 (Light Hazard) or NFPA 13R.

D. 10: This number of design sprinklers is incorrect for an NFPA 13D system and is not specified within the standard for this type of occupancy.

1. NFPA 13D, Standard for the Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes, 2022 Edition.

Section 8.1.1: "The system shall provide a discharge of not less than 18 gpm (68 L/min) to any single operating sprinkler and not less than 13 gpm (49 L/min) per sprinkler to the two most hydraulically demanding sprinklers."

Section 11.2.2.2: "The number of design sprinklers shall be the one or two sprinklers that are the most hydraulically demanding, as identified in accordance with Section 8.1."

2. SFPE Handbook of Fire Protection Engineering, 5th Edition.

Chapter 21, "Automatic Sprinkler System Calculations," Section 21.5.3, "Residential Sprinkler Systems." This section explains that for NFPA 13D systems, the water supply must satisfy the greater of the two conditions (one sprinkler at 18 gpm or two at 13 gpm each). It clarifies that the two-sprinkler calculation, requiring 26 gpm, is typically the governing design criterion. (DOI: 10.1007/978-1-4939-2562-421)

3. Oklahoma State University, Fire Protection & Safety Engineering Technology Program Courseware (FST 3333 - Fire Sprinkler Systems).

Module on Residential Sprinkler Design: Course materials consistently emphasize that NFPA 13D hydraulic calculations must be based on the more demanding scenario, which is the operation of the two most remote sprinklers, each discharging a minimum of 13 gpm.