The biggest threat at the Libyan fuel tank fire is the liquefied petroleum gas, which is in pressured vessels. International fuel fire expert Niall Ramsden talks us through the worst-case scenario.
DW: You have years of experience in dealing with fires, such as the one in Libya, around the world. What's the best way to put the fire out?
Niall Ramsden: The most normal method of extinguishing a fire is to use firefighting foam. And you can either do that with fixed systems […] or mobile equipment. So the most conventional way to deal with this particular situation would be mobile foam canons. You throw special firefighting foam onto the surface of the fuel and essentially prevent the vapors from rising and mixing with oxygen, so then you cannot have the fire.
But the fighting near the fires has made it difficult for firefighters to do their job. Couldn't you just let the fires burn out?
That is one possibility - a controlled burnout. Ideally, if a tank is built to a recognized standard, then that would be quite acceptable for most types of fuel, such as gasoline. The tanks should just fold inwards and collapse as the product burns off. And there have been several cases around the world where exactly that has happened. The issue then is to make sure it doesn't spread to other tanks, to prevent escalation, or indeed spread to something worse, like residential [areas], but then people can evacuate, of course.
But I understand - I'm not absolutely certain - there are some vessels containing liquefied petroleum gas (LPG) near these gasoline tanks. That product is in pressure vessels and if that is exposed to too much heat and the tank ruptures, then you get a massive fireball, which can escalate the incident considerably.
So one of the priorities, if you are going to allow the tank to burn out, is to make sure that anything that is exposed to fire is cooled - and you don't allow the fire to escalate.
Is it possible to extinguish such fires with water dropped from planes?
It is an unusual tactic for tank firefighting. It has been tried on one or two occasions - for example after the Turkish earthquake and some people claimed success using that technique. It wasn't just water, there were some chemicals in the water. But in reality that is a very unusual way of doing things. It's not reliable. And in Turkey it actually disrupted other firefighting operations. So I'm not convinced. It has not really worked in the past and I'd have doubts about it in the future.
What happens when a tank collapses?
The tank should burn out without collapsing - if they're built correctly. So the product should stay in the tank and the tank gradually burns down with the product, and it should not escape into - what I call - the bund area; some people call it the dyke area. There are some issues: for example, there will be flanges on the pipe work in the bund area - when they get hot, they might split and allow product to come out - or indeed some pipe work might fail. So the idea is that the secondary containment should contain it all. If it is sized properly, there will be some allowance, not much, but some allowance for additional firefighting foam and water containment as well. So the bund area should contain at least the contents of one tank plus ten percent more to allow a little bit for firefighting.
What would be the worst-case scenario with the pressure vessels?
When those vessels that hold that liquid are subjected to a lot of heat, eventually the tank can rupture, and the liquid that is inside really wants to be a gas at normal atmospheric pressure. So when the vessel ruptures that liquid immediately turns to gas and you get a massive fireball. It tends to be a fairly short-lived event, but at a very high rate in heat levels which can cause a lot of escalation - and fragments from the vessel can travel hundreds of meters. There have been situations where fragments have gone well over a thousand meters.
So the area should be evacuated...
Yes, they should be evacuating the area, and they should be cooling the tank. But I understand there are problems with getting water supplies.
And what threat do the gases pose?
It's always an issue - a big black smoke plume and nobody likes to see it. But take the Buncefield fire, which was one of the biggest in Europe - more than 20 tanks were burning. There were a lot of air quality measurements being taken at the time, and in reality down at ground level and at a reasonable distance from the fire there was no noticeable bad effects on people. Obviously, if you sit in the smoke plume itself, you're going to be in trouble. But in reality it didn't cause a major issue to public health.
But it can cause environmental damage.
Yes, if there's spill off from the product and from the firefighting foam, it can cause quite a lot of pollution around the area, depending on which direction it runs. It's yet another issue the firefighter has to consider when they decide what tactics to use.
Dr Niall Ramsden is the director of Resource Protection International, an independent consultancy. He has worldwide experience in fire hazard management in the oil, gas and petrochemical industries.