Ontario Office of the Fire Marshal (OFM) Firefighter II Certification Practice Exam

A boiling liquid expanding vapor explosion (BLEVE) typically occurs when a pressurized liquid in a container is heated to the point that it vaporizes rapidly, resulting in a violent explosion. The primary factor that leads to a BLEVE is insufficient cooling of the storage tank when exposed to fire or high heat.

When a tank containing a volatile liquid is subjected to external heat, if enough water or cooling measures are not applied to keep the tank cool, the pressure inside the tank can increase significantly as the liquid heats and vaporizes. If the pressure exceeds the design capacity, it can cause the tank to rupture, leading to a BLEVE.

While other factors, such as flames contacting relief valves or slow deterioration of the tank, may contribute to unsafe conditions, they are not the common or typical causes of a BLEVE. The rapid transition of boiling liquid to vapor is the critical mechanism that drives this dangerous scenario, which underscores the importance of maintaining adequate cooling in fire situations involving pressurized liquid containers.