The linked video was released immediately after the blast at the port city of Tianjin China.
The proximate cause of the huge explosions is evident in the video.
Note in the early part of the video that a fire has started in the port, and that the flames are directly impinging on one of three spherical storage tanks. Such tanks are used virtually exclusively to store liquefied flammable gas under pressure. A number of things are "wrong" in the video.
First of all, although flames are directly impinging on one of the three storage spheres, there is no water deluge on the spheres that should be supplying cooling. A design feature of all such spheres is typically a high-volume water deluge system that is intended to keep the spheres cool in the event of external fire. In the Tianjin video, the deluge has either failed or was never installed.
This means that as the flames impinge on the spheres not only does the internal pressure rise from the heat, but also that the metal of the sphere itself is being weakened by the heat of the impinging fire.
The second alarming thing about the video is that although the storage spheres are fitted with relief valves atop the spheres, none of the relief valves are lifting. If the pressure in the sphere was rising (as it must have been) from the heat of the external fire, then the relief valves, intended to protect the sphere in fire case, should have been relieving large amounts of flammable gas to the atmosphere. In such a case, the vent pipes from the relief valves, that point straight up, should have been shooting large jets of fire for long distances as the relief valves dropped the sphere's internal pressure. There is no such discharge from the relief valves.
This means that the internal pressure in the tank is steadily rising.
And a third thing - In the middle of the video, fire trucks are shown arriving at the facility and firemen are running to set up hoses. The fire, however, has already been impinging on the sphere for the time that it took for the firemen to be notified, the time that it took for the firemen to arrive at the scene, and the time that it took for the firemen to set up & prepare to fight the fire. This total time almost certainly exceeded 15 minutes.
The 15 minute time is significant because any liquefied flammable gas sphere that has been directly impinged on by external fire for 15 minutes or more is going to fail. The metal of the sphere has already been softened to the point where a "bubble" forms on the sphere. The bubble, inflated by the much higher than design pressures inside the sphere will eventually burst. When it does, a phenomenon called a Boiling Liquid Expanding Vapor Explosion (BLEVE) occurs. In such an event, the entire flammable contents of the sphere are instantly ejected under pressure from the sphere bubble bursting. The massive explosion that results is incredibly violent (in the Tianjin explosion, equivalent to 22 tons of TNT).
The final seconds of the video depict the firefighters, mere yards away from the sphere, trying to cool the sphere with their fire hoses. Their efforts were doomed to failure by their delay in starting the cooling process. What the fire-team leader should have done was to evacuate the area as quickly as possible and allow the spheres to BLEVE without personnel in proximity.
Although the Tianjin tragedy can't be undone, the opportunity for learning can save many lives in future situations.
1. Ensure that all bulk-storage liquefied flammable gas containers have functional deluge systems that are tested and reliable 2. Ensure that the same containers are fitted with relief valves designed for fire case.
1. Evaluate how long the spheres or containers may have suffered direct flame impingement. If it is even possibly 15 minutes or more, DO NOT try to cool the vessel - it is destined to fail anyway. 2. EVACUATE the area to prevent loss of life and let nothing delay that evacuation. The videos of the Tianjin BLEVE and other BLEVE videos online provide excellent training material for how violent such events can be. One to two miles is a reasonable minimum evacuation distance, and should be increased if large quantities of liquefied flammable gasses are at risk.
I remember watching early vids surface and wondering what blew up that created such a violent/sudden explosion. Scott
I can't guarantee that my analysis is the correct one, but the proximity of the storage spheres and the things I noted in the video lead me to believe that my guess is the right one. Even large quantities of sodium cyanide (the component that the news feeds seem to be focusing on) shouldn't have created an explosion of the magnitude shown, but the storage spheres could (easily) have.
The initial large explosion was probably the first sphere going, and the subsequent explosion would have been shrapnel from the first sphere puncturing the other spheres. The flaming debris shown in the videos on the outside of the fireball is probably the shrapnel from the storage spheres.
I've worked in chemical process operations & safety all my life, and although I've never seen a BLEVE first hand, I'm quite familiar with the causes & effects.
Boomzilla - (moniker NOT related to the explosions at hand...)
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