Fire behaviors of polymers under autoignition conditions in a cone calorimeter Long Shi n , Michael Yit Lin Chew Department of Building, National University of Singapore, Singapore 117566, Singapore article info Article history: Received 24 August 2012 Received in revised form 3 June 2013 Accepted 3 September 2013 Keywords: Spontaneous ignition Non-charring polymer Heat release rate Mass loss rate Thermal thickness Cone calorimeter abstract Besides piloted ignition, autoignition is also an important aspect to real fire development as combustible materials may be ignited without independent flame. Fire behaviors of non-charring and charring polymers were then investigated in a cone calorimeter under autoignition conditions. Fire risk of non- charring polymers are higher than those of charring polymers because of high heat release, and the increase of heat release rate is much obvious with a higher heat flux or thickness. Charring polymers seem to have a higher CO yield, while non-charring polymers have a higher CO 2 yield. Ignition methods have influences to combustion efficiency of non-charring polymers as effective heat of combustion under autoignition are observed lower than those reference data under piloted ignition conditions. Its influences to charring polymers are not obvious. Both CO and CO 2 yields under flaming combustion are higher than those under non-flaming combustion, but mass percent of carbon seem to has limited effect. Experimental data in this study can provide a guidance to fire risk evaluation of non-charring and charring polymers. & 2013 Published by Elsevier Ltd. 1. Introduction Ignition may be defined as that process by which a rapid, exothermic reaction is initiated, which then propagates and causes material involved to undergo change, producing temperature greatly in excess of ambient [1]. There are two types of ignition, namely piloted ignition – in which flaming is initiated in a flammable vapour/air mixture by a ‘pilot’, such as an electrical spark or an independent flame – and autoignition (or spontaneous ignition)—in which flaming develops spontaneously within the mixture [1]. Piloted ignition of a solid might very roughly be considered as occurring when lower flammability limit of a pyrolysate/air mixture is first reached, while autoignition of a solid might be considered to involve the autoignition of pyroly- sates [2]. Besides piloted ignition, autoignition process is also an important aspect to describe real fire development as combustible materials may be ignited without acceleration of spark plug or independent flame under specific situations. Combustible materi- als have been well investigated under piloted ignition [3–11], however, few studies have focused on fire behaviors under auto- ignition conditions. Combustible materials showed different fire behaviors under piloted ignition and autoignition conditions. From statistical analysis of experimental results, Melinek [12] noticed that minimum rate of volatile emission can be used to predict ignition, which is about 5.1 g/ m 2 s for piloted ignition and 7.7 g/m 2 s for autoignition. Different empirical models on ignition time were obtained for woods under piloted ignition [2, 13] and autoignition [14, 15] conditions. A correla- tion of ignition time for woods under piloted ignition and autoignition was obtained by Babrauskas [13]. It was shown that autoignition time are longer than piloted ignition time, and difference between these two becomes smaller as external heat flux rises. Minimum heat flux under autoignition also were found to be much higher than those under piloted ignition [2]. Cain [16] obtained that average minimum heat flux under autoignition are about 2.37 times of those under piloted ignition. External heat flux was found to impact fire behaviors of combustible materials. Shi and Chew [17] investigated fire beha- viors of woods under autoignition in a cone calorimeter. Experi- mental results showed that CO yield are less than 0.025 g/g when external heat flux are higher than 50 kW/m 2 , but they become higher than 0.04 g/g under 25 kW/m 2 heat flux. Luche et al. [4] investigated influences of external heat flux to fire behaviors of black PMMA in a cone calorimeter. It was observed that average MLR increases linearly with external heat flux. Gas production show differences when materials are under non-flaming and flaming combustions. Non-flaming combustion (also called pyrolysis) is used to refer to a stage of fire before flaming combustion has occurred [2]. Flaming combustion is defined as an exothermic oxidation reaction that takes place in Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/firesaf Fire Safety Journal 0379-7112/$ - see front matter & 2013 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.firesaf.2013.09.021 n Corresponding author. Tel.: þ65 83818700. E-mail addresses: shilong@mail.ustc.edu.cn, shilong@nus.edu.sg (L. Shi). Fire Safety Journal 61 (2013) 243–253