The minimum number of sprinklers required in a design area is calculated by dividing the total design area by the maximum allowable protection area per sprinkler for the specific hazard classification. According to NFPA 13, for an Ordinary Hazard occupancy using standard spray sprinklers, the maximum protection area per sprinkler is 130 ft².

The calculation is as follows:

Design Area / Maximum Area per Sprinkler = 1,500 ft² / 130 ft² = 11.54 sprinklers.

Since a fraction of a sprinkler cannot be installed, the result must be rounded up to the next whole number. Therefore, a minimum of 12 sprinklers are required to cover the design area.

B. 14 sprinklers: This number is higher than the calculated minimum and would result from using a smaller, non-standard coverage area per sprinkler (approx. 107 ft²).

C. 18 sprinklers: This is significantly more than the minimum required and would represent an inefficient design for the specified hazard and area.

D. 20 sprinklers: This number is substantially greater than the minimum required by the standard, leading to an unnecessarily conservative and costly installation.

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

Table 10.2.4.2.1(a) "Protection Areas and Maximum Spacing for Standard Pendent and Upright Spray Sprinklers for System Design." This table explicitly states that for an "Ordinary Hazard" occupancy, the maximum "Protection Area of Coverage per Sprinkler" is 130 ft² (12.1 m²).

Section 27.2.2.1.3 "The number of sprinklers in the design area shall be determined by dividing the size of the design area (ft² or m²) by the area of sprinkler protection (Aₛ)." This section provides the methodology for the calculation.