If you need to place smoke detectors in a room that is 40′ long by 15′ wide and has a smooth ceiling, what is the minimum number of detectors required?

If you need to place smoke detectors in a room that is 40′ long by 15′ wide and has a smooth ceiling, what is the minimum number of detectors required?

• A. 1
• B. 3
• C. 2
• D. 4

Answer: (C)

Smoke detectors on smooth ceilings should be placed so that no point in the room is farther than a specified distance from a detector. In many practice scenarios this distance is 15 feet. To meet that spacing in a room that is 40 feet long and 15 feet wide, you line up detectors along the length with about 15 feet between them. With a 40-foot length, you’ll need three detectors to keep every point within 15 feet of a detector (one around 7½ ft from the short wall, the next about 22½ ft, and the last about 37½ ft). The width is 15 ft, so a single row along the centerline covers it as well. Using only two detectors would risk creating a spot more than 15 feet away from the nearest detector, so three is the minimum.

Smoke detectors on smooth ceilings should be placed so that no point in the room is farther than a specified distance from a detector. In many practice scenarios this distance is 15 feet. To meet that spacing in a room that is 40 feet long and 15 feet wide, you line up detectors along the length with about 15 feet between them. With a 40-foot length, you’ll need three detectors to keep every point within 15 feet of a detector (one around 7½ ft from the short wall, the next about 22½ ft, and the last about 37½ ft). The width is 15 ft, so a single row along the centerline covers it as well. Using only two detectors would risk creating a spot more than 15 feet away from the nearest detector, so three is the minimum.