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Last night, Sunday 18 January 2009, there has been an incident reported on Pertamina Fuel Depot in Plumpang, North Jakarta. I was made informed by bunch of tweets from @jtug members. Relying on their information I’m trying to analyze the event based on the following presented facts:

1. There has been one big explosion followed by two smaller explosion.

2. The tank that explode only 30% full of premium grade fuel, at approximately 1500 thousand of liters.

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DISCLAIMER :

The following presentation may or may not be the scenario on what has happened at the incident, I’m trying to draw possibilities and not a conclusive statement on the following post. There might be other possibilities that I may have missed out in this post. The final conclusion shall be from the investigative authorities.

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In the event of fire and/or explosion there’s always three elements involved : Fuel, oxygen, ignition source. Based on the facts from eyewitnesses and media coverage, and based on my knowledge in the field of Loss Prevention and Process Safety engineering, which at the moment is far below the expert category, I came up with two scenario. Scenario one is the BLEVE scenario, scenario two is delayed ignition of hydrocarbon vapor containment.

BLEVE scenario

BLEVE is an acronym of Boiling Liquid Expansion Vapor Explosion. This is a type of explosion that can occur when a vessel containing a pressurized liquid is ruptured. Such explosions can be extremely hazardous.

A BLEVE results from the rupture of a vessel containing a liquid substantially above its atmospheric boiling point. The substance is stored partly in liquid form, with a gaseous vapour above the liquid filling the remainder of the container.

If the vessel is ruptured — for example, due to corrosion, or failure under pressure — the vapour portion may rapidly leak, lowering the pressure inside the container. This sudden drop in pressure inside the container causes violent boiling of the liquid, which rapidly liberates large amounts of vapour in the process. The pressure of this vapour can be extremely high, causing a significant wave of overpressure (an explosion) which may completely destroy the storage vessel and project fragments over the surrounding area. BLEVEs can also be caused by an external fire near the storage vessel causing heating of the contents and pressure build-up.

By assuming that the storage tanks are operating at near atmospheric condition and hence it is not pressurized vessel, it is more likely that the BLEVE is caused by external fire near the storage tank that leads to explosion. The fire engulf the tank and heating the fuel contained inside the tank which then boiled and vaporize, increasing the pressure inside, up to certain point where the tank integrity is collapsed due to pressure and heat from the fire. By the time the pressure inside the tank is high enough to break the tank wall, explosion occurred.

Based in this scenario, there are some question I would like to post.

1. If it’s an external fire that causes the BLEVE, is there any leakage from the tank or any other source of fuel?

2. If there is a leakage, will there be a sufficient heat to cause an ignition? please note that this incident happened in the evening.

3. If the heat is not sufficient to ignite the fuel, what other possibility of ignition source to fullfil the triangle of fire?

4. Before explosion occurred, is there any mitigation effort to prevent the fire from escalating that leads to catastrophic incident?

Delayed ignition of hydrocarbon vapor accumulation Scenario

The second scenario is delayed ignition of hydrocarbon vapor containment. This scenario could happen without preceded by fire. This also has two possibilities, explosion from inside the tank and explosion outside the tank. If the explosion happen inside the tank, it is possible that from the fact the tank is less than half filled with gasoline, there is quite big of void fraction inside the tank that can create hydrocarbon vapor and air mixture. Which in time will reach the Lower Explosion Limit (minimum fuel vapor in air concentration needed to create flammable/explosive mixture). All we need now is an ignition source to fullfil the fire triangle and ignite the explosion.

If this is the scenario, I would like to post few question:

1. What is the most likely ignition source to ignite the mixture? Is there any electrical device inside the tank that might be faulty and create electrical sparks?

2. Shouldn’t there be tank blanketing system (fuel gas or inert gas) to prevent the formation of hydrocarbon vapor and air flammable/explosive mixture inside the tank?

Another scenario is the explosion occured outside the tank (unconfined). This possible if there is leakage from the tank and release the vapor out. Over time, the vapor accumulates and create an vapor cloud, big enough (at least until LEL reached) waiting to be ignited from an igintion source. This can be anything, from heat, electrical sparks, lightnings. In the open environment, the air change is so rapid that it will dilute the vapor and prevent it from creating LEL mixture of HC vapor and air. Strong wind will easily wipe out the accumulated vapor. However, the gasoline vapor is heavier than air, which might be accumulated near ground level. Judging that the depot is located by the sea shore, and strong wind usually occurred by the bay, I would like to dismiss this scenario since the likelihood is so low.

From the field, we have the fuel, the oxygen but we missed out one thing, the ignition source. And that’s what we are trying to find out. It is now up to the investigative authorites to carry out their investigation and I would expect that their findings made public, this could be lesson learn for everyone, that safety culture is the most important and integral part in our daily lives.

Please feel free to discuss this issue, I am open to suggestion. Comments with a good netiquette highly appriciated.

PS : Now I miss my consequence modeling days… FLACS would be helpful for modeling and simulating the explosion.

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