Fire Safety Science Digital Archive

Experimental results are presented of the piloted ignition delay time and the upward flame-spread rate over the surfaces of insulated electrical cables under an externally applied radiant flux. The objective of the experiments was to assess and rank the fire performance of seven types of complex cables commonly used in electrical installations. The experiments were carried out with 46 cm long single cables that were suspended vertically and exposed to irradiance levels ranging from 0.5 - 2.5 W/cm². Some of the cables had a conducting core, and some did not. A simplified analysis, similar to that developed by Quintiere and coworkers was developed to identify the parameters that dominate the fire characteristics of the cable. A method similar to that proposed by the above authors was applied to develop flammability diagrams and to define the flame spread properties of the cable materials in an attempt to assess and rank the fire performance of the seven types of cable. It is shown that the method can be successfully applied and that it provides a simple way to rank the cables and to calculate the parameters important to ignition and flame spread in electrical cables. The study also explores the feasibility of predicting the piloted ignition performance of the cable insulations using thermogravimetric analysis (TGA) data in conjunction with the ignition and flame spread formulas by proposing that the surface temperature at which thermal degradation produces pryolyzate is related to the ignition temperature for that particular material. The predicted ignition delay times are compared with experimental results and it is shown that for most polymers, the temperature at which thermal degradation is first observed can be used to estimate ignition delay times, particularly at high irradiance levels.