The minimum required water flow from a single sprinkler is determined by multiplying the required design density by the sprinkler's coverage area. According to NFPA 13, an Ordinary Hazard, Group 1 occupancy requires a design density of 0.15 gpm/ft². The question specifies that each sprinkler has a coverage area of 120 ft².

The calculation is as follows:

Minimum Flow (q) = Design Density (d) × Sprinkler Coverage Area (As)

q = 0.15 gpm/ft² × 120 ft²

q = 18 gpm (68.1 lpm)

Therefore, the minimum water required from each flowing sprinkler is 18 gpm.

A. 12 gpm (45.4 lpm): This flow rate would result from an incorrect density of 0.10 gpm/ft², which is applicable to Light Hazard occupancies, not Ordinary Hazard, Group 1.

C. 20 gpm (75.7 lpm): This flow rate does not correspond to the standard density for the given occupancy and coverage area. It would require a non-standard density of approximately 0.167 gpm/ft².

D. 24 gpm (90.8 lpm): This flow rate would be correct if the occupancy were Ordinary Hazard, Group 2, which requires a higher density of 0.20 gpm/ft² (0.20 gpm/ft² × 120 ft² = 24 gpm).

1. NFPA 13, Standard for the Installation of Sprinkler Systems (2022 Edition).

Section 19.3.3.2.3: This section specifies the requirements for the area/density method.

Figure 19.3.3.1.1, "Density/Area Curves": This figure explicitly shows that for an Ordinary Hazard, Group 1 occupancy, the required design density is 0.15 gpm/ft² over a design area of 1500 ft².

Section 8.5.2.1: This section provides the formula for the minimum required discharge from a sprinkler as q = d × As, where q is the minimum required discharge, d is the design density, and As is the sprinkler protection area.

2. SFPE Handbook of Fire Protection Engineering (5th Edition).

Chapter 21, "Automatic Sprinkler System Calculations," Section 21.4.2, "Density/Area Method": This section details the procedure for hydraulic calculations using the density/area method. It confirms that the required flow from the most remote sprinkler is calculated by multiplying the specified density by the area protected by that sprinkler. (DOI: https://doi.org/10.1007/978-1-4939-2562-421)

3. Brock, Pat D. Fire Protection Hydraulics and Water Supply Analysis (3rd Edition). Oklahoma State University Fire Protection Publications.

Chapter 6, "Hydraulic Calculation of Sprinkler Systems": This chapter explains the density/area design method, reinforcing that the starting point of the calculation is to determine the flow from the most remote sprinkler by multiplying the required density (from NFPA 13) by the sprinkler's area of coverage.