An experimental study on upward flame spread over corrugated cardboard used in underground logistic transportation: Influence of grain orientation and thickness

摘要

Corrugated cardboard is widely used in underground logistic transportation and warehousing and it has become an important fire hazard source. According to previous warehouse fire studies, upward flame spread on corrugated cardboard plays an important role during the initial stage of warehouse fires and can decide the occurrence of subsequent increasing fire hazards. However, the wavy structural effect of corrugated cardboard on fire spread still lacks enough attention. This work studies the fire spread behavior of vertically-set corrugated cardboard with thicknesses of 1.5 mm, 3.0 mm and 4.0 mm. The cardboard inner hollow gaps are set either parallel (defined as along grain direction) or perpendicular (defined as across grain direction) to buoyancy direction. Experimental results show that: (1) along grain sample has better flammability than across grain sample; (2) the relationship between flame height (or pyrolysis height) and time has a best fit with power law, and the difference of the exponents between two grain orientations decreases with the increasing of the sample thickness; (3) for cardboard of different grain orientations and thickness, the ratio of average flame height to average pyrolysis height is a constant. The hollow gaps inside along grain sample, working as passage, are beneficial for the transportation of heated pyrolysis gases and preheating of upper virgin area, hence increasing burning rate and flame upward spread. However, it is observed that the phenomenon (flame luminance, delamination of front layer, extinguishment of flame base, etc.) difference between different grain orientations decreases as sample thickness increases. This study reveals the effects of grain orientation and sample thickness on the corrugated cardboard fire spread behavior which is common in commodity fire in underground logistic transportation and warehousing. The conclusions are beneficial for fire risk assessment as well as the improvement of related codes and regulations.