Back in June of last year (2020), the city of Wenling in China experienced a tragedy that involved a COLD BLEVE of a flammable liquified pressurized gas tanker truck and a subsequent explosion killing 18 people. We have dashcam footage of the COLD BLEVE and it is “textbook” footage of such an event – we even have the tanker rocketing through the air. I am not sure what the flammable gas was, as some news reports claim it to be LPG/Propane and others claim it was LNG/Liquified Natural Gas. We just know three things from the video footage:
1) it was a COLD BLEVE
2) It was a flammable LPG
3) It ignited and exploded as an unconfined vapor/gas cloud with a very fast flame propagation rate
We can be 99% sure this was a COLD BLEVE based on the video footage. We see the massive gas cloud forming and from it emerges the flying tanker across the roadway and then moments later the gas cloud, which has fallen into its flammable range, finds an ignition source.
Most safety professionals and emergency responders who work around flammable gases will be familiar with a HOT BLEVE, where we have flame impingement on the container leading to failure of the container. A COLD BLEVE is simply caused by a catastrophic failure of the container, usually from a direct impact. The USA suffered a cold BLEVE back in 2016 in Alabama when a Propane Tanker truck flipped over and the tanker got ripped open. As soon as the container goes “atmospheric” the contents, which were being kept in liquid states by its vapor pressure within the container, begin to boil rapidly. All of that energy wants to exit the tanker through the opening and it will send the container off like a rocket. Some gases may ignite as they exit the container from the static generated, but oftentimes there is no ignition – until the subsequent cloud dissipates and falls into its flammable range and then finds an ignition source, which could be hundreds of yards away from the actual incident. There have even been events, much like I think happened in China in 2018, where the flying tanker travels thousands of feet and as it loses energy and comes to a resting location, that could (already in a lesser concentration) find an ignition source and begins the explosion, which then travels back through the flammable cloud the container left in its travels. The gases are usually at ground level due to their vapor density and/or the fact that they are extremely cold immediately following the “COLD” BLEVE.