Ignition and Burning of Fibreboard Exposed to Transient Irradiation

Abstract

Natural materials like wood are increasingly used in the construction industry, making the understanding of their ignition and burning behaviour in fires crucial. The state of the art of wood flammability is based mostly on studies at constant heating. However, accidental fires are better represented by transient heating. Here, we study the piloted ignition and burning of medium density fibreboard (MDF) under transient irradiation. Experiments are conducted in a Fire Propagation Apparatus under parabolic heat flux pulses with peak irradiation ranging from 30 to 40 kW/m 2 and time-to-peak irradiation from 160 to 480 s. The experimental results reveal that the critical conditions for ignition of fibreboard vary over wide ranges: mass flux between 4.9 to 7.4 g/m 2-s, surface temperature between 276 to 298°C, and heat flux between 29 to 40 kW/m 2. Flameout conditions are studied as well, with observations of when it leads either to extinction or to smouldering combustion. We explored the experiments further with a one-dimensional pyrolysis model in Gpyro and show that predictions are accurate. Assuming a non-uniform density profile (a realistic assumption) improves the predictions in comparison to a uniform density profile by increasing the mass loss rate by 12%, decreasing the temperatures by 45%, and increasing the ignition time by 20 s. These results further support previous findings that a single critical condition for igntion or flameout established under constant irradiation does not hold under transient irradiation which indicates that ignition and extinction theories need improvements.

Critical Ignition Conditions of Wood by Cylindrical Firebrands

“…Studies on transient heat flux (Bilbao et al, 2002;Lizhong et al, 2007;Zhai et al, 2017;Gong et al, 2018;Santamaria and Hadden, 2019) have investigated time to ignition for transient as opposed to constant heat flux, including investigating the ignition criteria of critical temperature, critical heat flux, and critical mass flux; however, these studies have focused on incident radiative heating. Studies by Vermesi et al (2016Vermesi et al ( , 2017Vermesi et al ( , 2020 have investigated ignition of various materials exposed to transient heat fluxes and found that dual-criteria may be more accurate to describe ignition rather than a single criterion.…”

Extinction of Wood Fire: A Near-Limit Blue Flame Above Hot Smoldering Surface

“…In the literature, the ignition of various timbers or wooden materials has been studied extensively to understand the initiation and growth of timber fires [10][11][12][13][14][15][16]. Like most flammable materials, the combustion limits and fire behaviors of timber materials can be influenced by both environmental (e.g., heating source, oxygen concentration, and wind velocity) and material (e.g., density, composition, moisture, and age) factors [17][18][19][20][21]. Moreover, timber, as a typical charring material, can sustain both flaming and smoldering combustion [13].…”

“…Emberley et al [9,15] further studied the self-extinction of flaming timber and CLT under external radiation and found the critical heat flux of 43.6 ± 4.7 kW/m 2 and the minimum mass flux of 3.93 ± 0.45 g/m 2 •s were required to sustain the flame. Vermesi et al [17] found that for engineered wood, the critical mass flux for flameout varied in a wide range (1.4-17 g/m 2 •s). Nevertheless, extinction of the flame is not the end of a fire, as it may be followed by the smoldering [31].…”

Fire Resistance Evaluation of New Wooden Composites Containing Waste Rubber from Automobiles

“…Therefore, solid wood results would be applicable to them. Vermesi et al [ 37 ] studied the ignition of fiberboards under transient irradiation. Surface temperatures at ignition were close to 300 °C for the majority of cases, with the exception being the parabolic flux, with a time to peak of 260 s and a peak irradiation of 30 kW∙m −2 .…”