- Author
- Thomson, H. E.
- Title
- Ignition Characteristics of Plastics.
- Coporate
- Edinburgh Univ., Scotland
- Report
- Thesis, 1998, 244 p.
- Keywords
- plastics | ignition | fire tests | literature reviews | radiative ignition | combustible solids | ignition delay | time lag | fire point | temperature | mass loss | fire retardants | computer models | radiation heat flux | flammability tests | mathematical models | thermogravimetric analysis | oxygen index
- Abstract
- The piloted ignition of a range of common thermoplastics has been studied by exposing horizontal samples (65 x 65 x 6mm thick) to irradiance levels in the range 10-4OkW/m2. Fine thermocouples attached to the exposed and rear faces allowed continuous monitoring of surface temperatures. A small H2 pilot flame was applied at 4 second intervals and the times to sustained ignition and the corresponding surface temperatures were recorded. Within the limits of experimental error and with the exception of PMMA at the lowest heat flux, ignition temperature showed no systematic dependence on radiation intensity or spectral characteristics of the source, although separate experiments indicated a dependence on surface area when this was reduced to less than ca 4cm2. Ignition delay times proved to be dependent not only on radiant intensity but also on spectral characteristics of the source and various other experimental variables. Similar observations were made when these experiments were repeated in the IS0 ignitability apparatus. A theoretical model for piloted ignition based on the numerical solution of heat transfer equations for a semi-infinite solid and with critical firepoint temperature as the criterion for ignition was developed. Improved predictive results were obtained by adapting the model to incorporate the effects of diathermancy and source emission/sample absorption interactions. An experimental rig was designed and constructed which allowed sample weight to be monitored continuously during experiments. The minimum rate of evolution of decomposition products necessary to support flashing and sustained ignition by pilot was determined for the range of thermoplastics studied previously. These results are significantly lower than results reported elsewhere. This may be attributed to differences in the convective heat transfer coefficient at the surface in the various experimental rigs. The effect of two different fire retardant systems on ignition was investigated by determining the firepoint temperature, ignition delay time and critical mass flux at piloted ignition for three fire retarded plastics and comparing these with the equivalent values for the unmodified parent materials. Limiting oxygen index (LOI) values were also determined. The fire retarded modifications exhibited higher values in all four measured parameters than their untreated counterparts.