We tend to associate boiling liquid expanding vapor explosions (BLEVEs) with hazardous materials incidents like rail cars or large propane fixed tanks at a commercial or industrial building. The reality is, however, that we can face these situations any place where there are pressurized cylinders.
In our corresponding video, we witness a situation where there are multiple oxygen cylinders present within the residential structure as well as a barbeque with a propane cylinder on the outside. This residential address is a single-story fourplex, which means there could easily be multiple propane cylinders in the backyard of each unit.
The responding Albuquerque fire crews find heavy smoke and multiple hazards that can easily compromise crew and occupant safety.
BLEVE basics
But first, a quick refresher on BLEVEs. A BLEVE involves a pressure vessel that contains a liquid fuel-like propane. In its normal state, the liquid is under pressure but still a liquid contained safely by the pressure vessel. Once a heat source is applied to the pressure vessel, like a fire, it starts to boil the liquid inside, causing an increase in pressure. As the liquid turns to a vapor, there will be an increase in the internal pressure, pushing against the walls of the vessel. At the same time, the heat source is weakening the vessel walls and at a certain point, the vessel structure will fail, causing an explosion.
BLEVEs are very dangerous. They have the capacity to create large fireballs that spread radiant heat. They also have the capacity to produce shrapnel that could easily injure firefighters.
Removing the trigger changes fireground tactics
The video shows a propane cylinder BLEVE as well as multiple oxygen cylinder explosions. An oxygen cylinder is not filled with a liquid but rather pure oxygen. This is still a pressure vessel containing a pressurized gas, in this case, pure oxygen. Even though they are exploding, they are not the result of a BLEVE but rather the result of the same trigger – a heat source.
The domino that needs to be removed in this chain reaction is the heat source. Removing the heat source means removing the trigger for the pressure vessels to fail. This means using large water streams from a distance, such as deck guns or ground monitors to put out the fire and to cool the cylinders.
In our video, we see crews mount a defensive strategy to extinguish the fire and cool the environment while simultaneously protecting fire personnel and the public. Once the initial hazard has been eliminated, crews are able to go back to an offensive mode to complete the tasks of search, fire extinguishment and overhaul.
Let’s underscore the point here: Whenever there are pressurized vessels present, do not be afraid to take a defensive position first, remove the heat source, then go in to finish off the rest.
Training time
After watching this video and reading this story with your company, take the following steps to engage in BLEVE-focused training:
- Review page 367 of the Emergency Response Guidebook to see how much water is needed for various sizes of pressurized cylinders when they are exposed to fire;
- Take a drive around your response district to identify and preplan large pressure vessels.
- Determine what is the best approach to take for a defensive position;
- Practice setting up master streams on a pressure vessel and apply water for a while; and
- Using the ERG, identify what size fireball will be created based on different size pressure vessels in the response district.
