Beam-type detectors are not normally affected by altitude above what value?

Beam-type detectors are not normally affected by altitude above what value?

• A. 1,000 ft
• B. 2,000 ft
• C. 3,000 ft
• D. 4,000 ft

Answer: (C)

Beam-type detectors rely on an optical path: a transmitter sends a light beam and a receiver detects light scattered by smoke in that path. Changes in the air along the path—air density, pressure, humidity, and particulates—can alter how much light is scattered or absorbed, which can affect the detector’s response. As altitude increases, air becomes thinner, reducing these atmospheric effects. Around 3,000 ft above sea level and higher, the air is sufficiently sparse that further altitude changes do not noticeably influence the beam’s performance. Hence, altitude above about 3,000 ft is not normally a factor for beam-type detectors. Local conditions like dust or humidity can still matter, but the altitude effect itself is negligible beyond that threshold.

Beam-type detectors rely on an optical path: a transmitter sends a light beam and a receiver detects light scattered by smoke in that path. Changes in the air along the path—air density, pressure, humidity, and particulates—can alter how much light is scattered or absorbed, which can affect the detector’s response. As altitude increases, air becomes thinner, reducing these atmospheric effects. Around 3,000 ft above sea level and higher, the air is sufficiently sparse that further altitude changes do not noticeably influence the beam’s performance. Hence, altitude above about 3,000 ft is not normally a factor for beam-type detectors. Local conditions like dust or humidity can still matter, but the altitude effect itself is negligible beyond that threshold.