Fire risk of dripping flame: Piloted ignition and soaking effect

Abstract

The dripping of thermoplastic fuels is a significant fire hazard, but the complex dripping-ignition process is still not fully understood. In this work, we investigate the ignition capability of continual polyethylene drips with the size of 2.6–4.6 mg and the frequency of 0.3–1 Hz. These flaming drips land on four groups of materials, cardstock papers (>0.1 mm), thin papers (≤0.1 mm), cotton, and porous mineral materials. For igniting cardstock papers, the minimum drip number decreases with the drip size and frequency, and the ignition time follows the piloted-ignition theory. The thin permeable paper and cotton are soaked by drips, so ignition only requires a small and fixed number of drips. The soaking effect also helps anchor the flame on drips absorbed by other porous mineral materials, showing a notable fire risk. Theoretical analysis of the ignition limit and delay time is proposed to identify the boundary between the piloted dripping ignition and the flame anchored on drip-soaked material. This research reveals different ignition mechanisms of dripping fire and helps understand the fire hazard regarding the transport and soaking effect of molten fuels.