When installing a heat-sensing fire detector on the bottom of a beam, the beam must be less than how many inches in depth?

Installing a heat-sensing fire detector on the bottom of a beam requires compliance with specific guidelines to ensure optimal performance. According to National Fire Protection Association (NFPA) standards, one critical consideration is the depth of the beam. When a beam is deeper than a certain threshold, it can inhibit the effectiveness of the heat detector due to potential heat stratification and the inability of the device to accurately sense temperature changes.

For installations, if the depth of the beam exceeds 12 inches, it may obstruct the detector’s ability to function correctly, leading to delayed activation or failure to detect a fire condition adequately. Therefore, the requirement to install the heat detector on a beam with a depth of less than 12 inches ensures that the detector can effectively respond to heat generated by a fire, promoting safety and enhancing the fire alarm system's reliability. In this case, the correct threshold for beam depth, where the heat-sensing detector can still perform effectively, is set at less than 12 inches, making that the valid choice.