The 5151 thermal detector meets the needs for applications where rapid response is vital and rapid temperature increases would only be caused by a fire emergency. The detector initiates an alarm in response to both rapid rate-of-rise conditions (increases in excess of 15°F per minute) and fixed heat (135°F). This enables the heat detector to communicate an alarm to the central control panel prior to reaching its fixed set point for high rates of rise, providing a timely response to both rapid and slow temperature increases.