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Wednesday, November 12, 2008

Modified NGV Burst and Killed a Person at Malacca

1. Shocked! As reported in the news, a trader who turned COOKING GAS CYLINDER into a natural gas vehicle (NGV) storage unit to power his van died hours after the tank exploded at a petrol station. The explosion is believed to have been caused by a spark from the engine, which was running at that time. The self-modified cooking gas cylinder was placed under the driver's seat and covered with a canvas. Looks how creative Malaysian is. This is one example of creativity that leads to deaths.

2. After reading the news report, a member of OSHA (Daud Sulaiman) has written things to differ the reason for the explosion written in the news. These are the facts which obviously are not available to the reporters.

3. An LPG cylinder is designed to maximum 20 bar - or 300 psi, to contain liquefied Propane (70%) and Butane (30%). The pressure only comes from the propane, as the butane has almost no pressure. Check your cigarette lighter. Pressure can build up only if the liquid is vaporised.

4. This is important. The NGV cylinder is something like a BA (breathing apparatus), with similar pressures. The steel tank is normally designed for 200 bar - or 3,000 psi, 10 times the pressure for the LPG! If you want more gas, you will have to use an even higher pressure but that will increase the thickness of the cylinder required, and the weight will become prohibitive. In which case, composite material is the alternative.

5. What happened in this incident is that the LPG sphere was filled beyond its capacity and exploded - this is a physical explosion! The gas released was ignited almost immediately by the engine which was running - and this caused a second fire explosion! But the timing could be very fast and almost simultaneous. Most people would not have identified it as 2 explosions.

6. As a result the public must be made aware of the fact that any LPG cylinder is 10 times inferior to the NGV cylinder, in terms of pressure. Use the LPG cylinder, and you will have a time bomb in your hands.

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6 comments:

Anonymous said...

creative yet stupid

tony

Anonymous said...

Salam and Greeting to all my respected senior and otai safety practioners,

Can someone verify to me, whether or not an 'under pressured' LPG cylinder can explode? Of course with source of ignition..If yes, how?

TQ so much

Best,

Azrul Zabidi
SAM Penang

Ir Daud said...

I do not understand what you mean by "under pressured" LPG cylinder.
Is the pressure lower than normal, or is the LPG cylinder under normal pressure?

I will just assume that the cylinder is under normal pressure.
There is liquefied pretroleum gas inside - it is liquefied by pressure. LPG contains 70% Propane and 30% Butane, and the pressure comes mainly from the propane.

If the LPG cylinder is left in the sun, the liquid will heat up, and more gases will evaporate, thus building up the pressure. If the safety valve has a low setting, the valve will soon be forced open and the gas will escape. If there is a source of ignition nearby, the gas can catch fire, and flashback can also happen - whereby the flame will follow the path of the gas and enter the cylinder - the result : the cylinder can fly off like a rocket, with the capacity to break down a concrete wall. I am serious.

Now if you are refering to the recent NGV explosion, that is a different story. This guy tried to fill in the LPG cylinder which is designed for low pressure (20 bar or 300 psi) with natural gas at more than 200 bar or 3,000 psi. Of course the LPG cylinder is not designed for that and it exploded - physically. The released gas then catches fire and explodes - this is a gas explosion.

If you can go to the CSB website : (Chemical Safety Board, USA) you can download a propane gas explosion video, and you will get a better understanding.

regards

Anonymous said...

Thank you Ir. Daud,

Roughly I get the idea of how an explosion can happen to LPG cylinder..build up of pressure..heat...ignition..etc...even the thickness of cylinder plays a role....
But recently I found something in the internet that I could not really understand....It said that one of the cause for an explosion is due to under pressure.. Could this be true? I'm not sure what it means since no explanation sufficiently given..or maybe there is no such thing as that..

Best,

Azrul Zabidi

ir daud said...

Of course the vessel is under pressure. Even a can of coke is under pressure ... but the pressure is low, around 3 bar or 45 psi. But if you fill the coke can to 30 bar, it is going to burst! because it cannot take that pressure.
the point is : can the vessel take that pressure? Is it designed to take that pressure?
The LPG cylinder is designed to take a pressure of up to 20 bar or 300 psi. The normal working pressure is less than that! maybe around 200 to 250 psi only.
But the NGV gas at the petrol station is at a pressure of more than 200 bar or 3,000 psi. can you understand that? the NGV cylinder is designed to take that pressure, therefore it can take 3,000 psi without bursting. But the LPG cylinder is designed for 1/10th that pressure - so when the pressure reaches maybe 40 or 50 bar, the LPG cylinder will crack and "explode" - this is a physical explosion.
I hope this is more clear to you

regards

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