An idealized temperature curve of compartment fire has three, distinct phases: growth phase, steady-burning (or fully developed) phase, and decay phase. Standard temperature-time curves are not suitable for describing the fire phenomena because it does not take into account fire load nor ventilation conditions, and fire according to these curves never decays. The temperature curve of compartment fire, especially the growth phase, may be treated like pulse phenomena. This means that it is possible to approximate the fire development with some suitable function that satisfactory describes the pulse phenomena. The shape of the time-temperature curve for fire with flashover has characteristic peak before the decay phase, or slow decreases before the decay phase - in absence of flashover. In this paper we propose the definition of the time-temperature curve by means of a unique function in which the quantities of fuel and ventilation conditions are defined with parameters. This function is very convenient for approximation of the development of compartment fire with flashover, for smouldering combustion which has fire curve without characteristic peak, this function can be used only for approximation of growth period of fire.

Alarm systems represent a combination of the various modern engineering solutions (electrical, mechanical, hydraulic, etc.) with the primary goal to protect human lives, living and working environment and material properties. Detectors are basic and common components of these systems. There are many different kinds of detectors which usage depends on system solutions, prices and other technical properties of system application. Different types of non-typical lines can be used as detectors in alarm systems, such as coaxial cables or special constructed electrical lines. The change of some parameters of cables, such as capacity, impedance, resistance or similar, according to temperature, pressure, torsion or other disturbances, can be used for detection of intruder or fire. This work presents experimental results obtained on three different types of coaxial cables: RF 75-3-1, RF 75-4-5 and RF 75-7-9 in order to show changes of capacity as a consequence of heating due to growth of surrounding temperature, and consequently, possible application of cables as fire detector. Before an experiment, a simulation of fire in laboratory 113 in Electrotechnical school Nikola Tesla in Nis was made in FDS (Fire dynamic simulator) software to show the possible spreading of fire, and consequently, to find optimal location for coaxial cables as fire detectors.

The main problem in fire detection using linear detectors, independently of its type, is a precise distance determination of fire from control equipment. This work presents experimental results realized on three different types of coaxial cables: RG U/6, RG 178 B/U and RG 122/U produced in cable factory in Jagodina, as well as simulation results realized in Pspice computer simulator. The aim of this paper is to show that temperature changes close to coaxial cable effect on some cable parameters, such as resistance, capacity, impedance, amplification, attenuation and others. This fact enables usage of coaxial cable for linear fire detection. Mentioned parameters could be used for fire distance determination from control equipment (fire control panel). This work is just a small part of a large investigation applied for realization of PhD thesis “Fire and burglary protection using non-typical electric lines” which were approved by University of Niš, evidence number 8/20-01-003/11-019.