What type of fire detector is typically the slowest to respond when a fire occurs?

Heat detectors are designed to respond to changes in temperature, making them typically the slowest type of fire detector when a fire occurs. They activate when the temperature rises to a predetermined level or when there is a rapid rate of temperature increase. This means that they require a certain amount of time for the heat from a fire to reach the detector and trigger an alarm, which inherently takes longer than smoke detectors or photoelectric detectors that can respond to the presence of smoke particles in the air.

In comparison, smoke detectors, particularly ionization detectors, are generally quicker to respond because they detect the presence of smoke from a fire almost immediately. Photoelectric detectors are also designed to identify smoke by utilizing light beams and can be sensitive to smoldering fires. Therefore, heat detectors, while useful for certain environments where smoke detectors might cause false alarms (like kitchens), are not as quick in alerting to a fire's presence.