A tanker carrying 20,000 tonnes of LPG is burning out of control of the coast of China. There are fears of an explosion. How big would such an explosion be?
Ships have been ordered to keep sixteen kilometers away!
-Oli
Of immediate concern is a Boiling Liquid Expanding Vapor Explosion (BLEVE for short) which is very common for liquified hydrocarbons tank fires.
Most firefighters are poorly trained to handle a BLEVE and in the past it has had devastating consequences for the firefighter as well as the fire.
This is explained mathematically here -
Investigation of an LPG accident with different mathematical model applications
So how much energy would such a blast produce? The fact that ships are being warned to stay sixteen k’s away suggests that it is approaching nuclear levels.
Projectiles from Blevy’s are known to go upto 20 kms (or was it miles ?) . Ok I have no cite for that - just sketchily remember it from seminar, I attended long back.
But there is published evidence that projectiles can go upto 30 times the fireball radius. So they are expecting the fireball to be about 500 m if they are asking people to stay away 16 kms. Well - I donno - I’m not a safety expert - but even if they expect the ball to be 200 m - its not too bad to play it safe.
Jeez. A 500m fireball is pretty darn big for a conventional explosion. Does that mean 500m hemisphere? That is, would the fireball from such a blast reach 500m vertically?
If so, then that is approaching a small nuclear blast.
-Oli
BLEVE is not a conventional explosion and it does’nt “always” happens. But it does happen sometimes with the “right” (or “wrong”) conditions.
Here’s a picture . See the size of the tanker , prolly a rail road tank and see the size of the ball of fire (I believe the fire pic was taken sometime after the explosion cos the photographer may have been startled).
So even if you go by the ratio in that picture and apply it to a Sea Vessel, maybe you come close to the size anticipated. But I may be wrong.
Would the explosive power increase in a linear fashion, though?
I should imagine that as you get larger amounts of fuel, the explosive power would diminish - that is, it would take longer for all the gas to be exposed to excess oxygen.
-Oli
Okay - I have a better site for you here . Look at the relative size of the bottles/tanks and the resulting fireball. There are videos too on that site.
Thanks for the link. It does give a better idea of the size of the explosion relative to the amount of fuel.
-Oli
There are simulation packages available t o calcultate the blevy evacuation distance like this. I would hope that someone ran the simulation before deciding the distance. The fireball depends on the amount of fuel and also the PRV (Pressure Relief Valve) Settings on the tank as well as the condition of the tank too.
If anybody’s interested, it’s still burning, hasn’t exploded yet.
http://www.alertnet.org/thenews/newsdesk/HKG150297
One of the things that makes BLEVE’s so dramatic is that the fuel is usually above its boiling point when the explosion occurs. This supersturated, superheated fuel then explosively breaches its container, converting to a cloud of vapor which is then ignited. It is already in a mist, fully exposed to plenty of oxygen when it goes. All of the steps i just listed happen in a fraction of a second. This is why in some cases fire departments will let a large propane tank blow rather than try to put out a fire near it. Fires and explosions attached to flammable gases and vapors are nasty business.