On the use of Fire Safety Engineering to Evaluate the Performance of Heat Detectors in High Ceiling Application

In the framework of design and installation of fire detection and fire alarm system in buildings, when high ceilings are involved, it is likely to run into the limits of the more common standards. Several regulations fix a ceiling height limit beyond which heat, smoke, and combustion gas detectors should not be mounted. Among the available technologies, the aspirating smoke detection (ASD) systems have the highest limit (i.e., 40 m according to BS 5839-1:2017). Nevertheless, this technology should not be used when processes that yield smoke, fumes, dust, etc., are present, and an alternative type of fire detector needs to be employed. This is due to the necessity to avoid false alarms, which is critical for successful fire detection and alarm systems. The concomitance of these two situations, i.e., dusty environments and high ceiling height, is not unusual in the industrial sectors. To investigate it, the state-of-the-art solution is adopting the principles of Fire Safety Engineering (FSE). The FSE is based on calculations that consider the conservation of mass and energy and permit to predict several crucial quantities such as the smoke temperature, smoke volume (and layer height), and species concentrations resulting from a fire of a given size (ISO/TS 13447:2013). In this work, a series of Computational Fluid Dynamics (CFD) simulations were conducted to assess the performances of a fire detection system composed of heat detectors installed at heights up to 20 m larger than the standard limit. The characteristics of an actual building adopted for storage of hazardous materials and a real heat detector system were considered. The temperature field resulting from two different types of t2-growth fire, i.e., one ultra-fast and one with slow evolution, were analyzed. The corresponding alarm times were evaluated and compared with ASD characteristics timings, recognized as a benchmark for its high sensitivity.