Fire Friday #1: Linear Heat Detection Response Time

Is it wrong to equate measurement time with response time?

A fiber optic Linear Heat Detection (LHD) system essentially consists of two elements: the interrogator unit and the sensor element, i.e. the fiber optic sensor cable itself. While the measurement time of such a system is exclusively a parameter of the interrogator unit, the response time of a fiber optic linear heat detector is determined and influenced by a multitude of parameters. These include the thermal behavior of the sensor cable, the cable installation method, the alarm parameter configuration, the fire type, the heat release rate (HRR) and environmental conditions such as wind speed. The thermal behavior of the sensor cable plays a special role here since it determines the response behavior of the overall system to a predominant extent and not – as is often erroneously assumed – the measurement time of the interrogator unit.


AP Sensing has spent a lot of time developing thermally optimized sensor cables that not only effectively detect convection heat, but are also very sensitive to radiant heat. The low thermal resistance enables rapid transfer of heat to the optical fiber, significantly reducing detector response time. 

Many fire tests (for example, fire tests according to RABT in Germany) have shown that we can detect a fire twice as fast as required by the guidelines. Due to optimized sensor cables, the AP Sensing fire detection system is also able to precisely localize the fire, regardless of the prevailing air flow and its strength. 

Another way to change the response time of the detector is by changing the alarm parameters. However, this should be done very sensitively, as incorrectly setting the alarm parameters undermines the false alarm resilience of the system. Therefore, a fast response time is not always desirable – at least not if the false alarm resilience suffers from it. The alarm parameters in AP Sensing's LHD system are freely configurable, but we offer sets of alarm parameters that have been tested by reputable institutes such as UL, FM and the VdS. This gives our customers the assurance to find an optimal balance between fast response time and false alarm resilience.

Response time, spatial resolution, and alarm zone configuration: what is important when selecting a Linear Heat Detection system? Find out more in our weekly series.

AP Sensing Fire Friday