The effect of temperature and ventilation condition on the toxic product yields from burning polymers

Abstract

A major cause of death or permanent injury in fires is inhalation of toxic gases. Moreover, every fire is unique, and the range of products, highly dependant on fire conditions, produces a wide variety of toxic and irritant species responsible for the most fire fatalities. Therefore, to fully understand each contribution to the toxicity it is necessary to quantify the decomposition products of the material under the test. Fires can be divided into a number of stages from smouldering combustion to early wellventilated flaming, through to fully developed under-ventilated flaming. These stages can be replicated by certain bench-scale physical fire models using different fuel-to-oxygen ratios, controlled by the primary air flow, and expressed in terms of the equivalence ratio (the actual fuel/air ratio divided by the stoichiometric fuel/air ratio). This work presents combustion product yields generated using a small-scale fire model. The Purser Furnace apparatus (BS7990 and ISO TS 19700) enables different fire stages to be created. Identification and quantification of combustion gases and particularly their toxic components from different fire scenarios was undertaken by continuous Fourier Transform Infrared Spectroscopy. The relationship between type of the fire particularly the temperature and ventilation conditions, and the toxic product yields for four bulk polymers, LDPE, PS, Nylon 6.6 and PVC are reported. For all the polymers tested, except PVC, there is a dramatic increase in the yield of products of incomplete combustion (CO and hydrocarbons) with increase in equivalence ratio, as might be expected. For PVC there is a consistently high level of products of incomplete combustion arising both from flame inhibition by HCl, and oxygen depletion. There is a low sensitivity to furnace temperature over the range 650-850°C, except that at 650°C PS shows an unexpectedly high yield of CO under well-ventilated conditions and PVC shows a slightly higher hydrocarbon yield. This demonstrates the dependence of toxic product yields on the equivalence ratio, and the lack of dependence on furnace temperature, within this range.

Fire Performance of Sandwich Panels in a Modified ISO 13784-1 Small Room Test: The Influence of Increased Fire Load for Different Insulation Materials

“…In under-ventilated flaming conditions the yields of the main asphyxiants (carbon monoxide, and hydrogen cyanide when nitrogen is available from the fuel) increase by a factor of 10 or more, making the effluent much more toxic than when burning in well-ventilated conditions [30,31]. In the PIR experiment with burner only, the peak CO is 3.75%, which is approximately 10 times the lethal concentration quoted in ISO 13344 [32], whereas the highest average HCN concentration of 150 ppm is approximately equal to the lethal concentration, each for 30 min exposure [32].…”

The role of isocyanates in fire toxicity

“…The steady state tube furnace (ISO TS 19700) was developed to replicate different stages of fires on a bench-scale (Stec et al 2008a). The principle of the ISO TS 19700 tube furnace is a fixed rate feeding of the sample into a furnace under a fixed air supply (Stec et al 2008b ;Stec & Hull 2010).…”

The effect of gas phase flame retardants on fire effluent toxicity

“…To assess the contribution of a material, or a composite article (such as a chair or a fuse box) to the fire toxicity, it is necessary to know both the rate of fire growth and the yields of the different toxicants. The composition of these effluents depends on the chemical formulation of the burning material, oxygen supply, temperature and heating rate [2,3]. The most toxicologically significant products are asphyxiant gases and incapacitating irritants.…”

“…It is therefore essential to the assessment of toxic hazard from fire that each fire stage can be adequately replicated, and preferably separating the individual fire stages. A number of different methods exist to assess fire toxicity [9], but most fail to relate the toxicity or toxic product yields to particular fire scenarios, or to replicate the most toxic under-ventilated conditions [3]. The steady state tube furnace (SSTF), ISO/DIS 19700 [10], was specifically designed to replicate individual fire stages.…”