When locating spot-type smoke detectors, all points on a smooth ceiling must have a detector within what fraction of the selected spacing?

The correct answer is based on the guidelines provided by recognized standards for the installation of smoke detectors. For spot-type smoke detectors, it is required that all points on a smooth ceiling have a detector within a specific distance to ensure adequate coverage and early detection of smoke. The guideline states that no point should be more than 0.7 times the selected spacing of detectors away from a smoke detector.

This means that if the detectors are spaced out at a certain distance, any point on the ceiling should not exceed 70% of that distance from the nearest detector. This standard ensures that any smoke that may arise in the area is detected promptly, maximizing safety and reducing the risk of fire hazards.

The other potential choices reflect distances that do not meet the established safety standards for smoke detector placement, making them less effective for smoke detection in a timely manner. Thus, the correct approach to enhancing safety through proper smoke detector placement involves adhering closely to this guideline, confirming that no point exceeds that 0.7 ratio from a detector.