STUDY ON THE COMBUSTION OF POLYMERS WITHIN COOLING TOWERS

摘要

It should be noted that all of the listed test approaches have successfully proven the characterization of flammability of polymer materials or products. However, there is no clear relationship reported between the test results of any of these test approaches. The LOI test uses the concentration of oxygen to characterize the flammability of the material. The cone calorimeter test focuses on the heat release during the combustion process. UL94 and the Steiner Tunnel Test simply represent the response of a material/product in a laboratory fire situation. Weil et al. found rather disappointing correlations between test results from cone calorimeter and LOI tests. Morgan, A. et al. investigated 18 thermoplastic materials with UL94 ratings from HB to VO, and they found a very rough correlation between peak heat release rate (PHRR) and heat release rate (HRR) at 60 seconds, however, no correlation with time to ignition or total release rate. Now that we know what polymer combustion is, what factors can affect it and what tests are currently available or being used in the cooling tower industry, can the cooling tower industry provide an owner or end user a test that will help them be able to gauge whether a potential cooling tower purchase has a high or low potential to have a fire event? Based on the above information, the answer would need to be "no". However, is there a group of current tests that could be used in conjunction with one another to get a very good indication, and improve upon the methods used today, of a cooling tower fill media's fire potential risk? The answer to that question looks to be "yes". Based upon the above information, the use of an LOI test in conjunction with the E84 test, which must be tested in accordance with CTI Standard 136 (2010), would provide for a more clear risk picture than what the industry is currently utilizing, especially over stating E84 without mention of CTI recommendations. Based upon this research and material testing, the recommendation for an owner wanting a lower risk fill media in their tower would be to have a material with an LOI of 40 or above in order to reduce the probability of the media to catch fire and to sustain that fire, as well as a product Flame Spread Rating of 25 or less, so that if there is an external fire source, the fire will spread as slowly as possible. The numerical results for both the E84 test and LOI can be easily provided for a product by the manufacturer and the LOI can readily be determined by the owner to confirm conformity to desired LOI, just like any other material conformity test. These two tests can provide a numerical comparison for a fill material and product and if an owner wishes to look a little deeper into risk factors the UL94, or ASTM D635, test and the cone calorimeter tests, specifically peak heat release rate (PHRR) and total heat release (THR), can provide further insight as part of the combustion process of fuel, heat and oxygen. In that case, a chart like the one listed below in Table 2, may be utilized as a reference to gauge a cooling tower fill media's fire risk potential. Note that the below chart does not take into consideration a fill media's sheet thickness or overall geometry which will play some role in the fill media's fire risk potential, but has not been be included in the scope of this paper.