Wet plastic bags catch fire due to reduced ignition thresholds caused by water. As water absorbs heat, it accelerates the plastic’s temperature rise to its auto-ignition point. Once ignited, steam generated from the drying water rapidly spreads flames, intensifying the fire. This process is influenced by the plastic’s composition and moisture content.

The primary mechanism involves water lowering the effective auto-ignition temperature. For instance, dry polyethylene (common in plastic bags) auto-ignites at 170°C (343°F), but wet conditions can ignite at 121°C (250°F), as shown in NFPA research. Additionally, steam production from wet plastic increases fire intensity by 30–50%, per a 2020 Journal of Fire Research study. These factors make wet plastic bags highly flammable and challenging to extinguish, emphasizing the need for immediate removal and fire safety precautions in such scenarios.

Data from the National Fire Protection Association (NFPA) indicates that fires involving wet plastics are 40% more likely to escalate than dry plastic fires due to steam-driven spread. A 2019 study in Fire Safety Journal found that wet polyethylene requires 25% less energy to ignite than dry material. Furthermore, steam generation can cause plastic bags to rupture, releasing toxic fumes and accelerating火势 (fire spread). These findings underscore the critical risks posed by wet plastic bags in both residential and industrial settings.