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Thread: CNG bus explosion - GIF

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    Altair's Avatar
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    CNG bus explosion - GIF

    CNG bus explosion in Stockholm, Sweden.




    Previously:

    Natural gas bus with gas bags - photo
    1917 natural gas-powered taxi - photo
    Cargo ship liquified natural gas tank - photo
    Natural gas sniffer truck - photo

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    Supporting Member Karl_H's Avatar
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    Karl_H's Tools
    As Alfred Nobel would say "Boom goes the CNG!"

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    Looks like the gas storage (cylinder?) ruptured then the atomised fuel ignited. Hope nobody seriously injured although that looks unlikely.

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    I just did a quick google search on this and miraculously, nobody was killed. The bus was empty except for the driver, who somehow escaped with serious injuries, but alive. I would never have believed that from looking at that video.

    A bit on the cause here:

    https://6abc.com/stockholm-bus-explo...weden/5181527/

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    jdurand's Tools
    I've seen several pictures of LNG vehicles blowing up, not having worked with it, does it have a very wide explosive concentration range or something?

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    Supporting Member DIYSwede's Avatar
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    DIYSwede's Tools
    This was LBG - "Liquefied BioGas" a k a Liquid Methane, extracted from sewage processing plants in Stockholm.

    CNG bus explosion - GIF-lbg-bus.jpg

    This case had a bunch of 7 cooled pressurized bottles on its roof, a driver trying to squeeze it under a (too) low underpass protection beam (seen mid-pic),
    a bottle was detached and pressed down into the compartment pouring out the LBG, which then turned into gas and then ignited.
    This gas having a burning range from 4,2-16% in air made the compartment explode, spilling the windows outside.
    Then this initial fire torched the still remaining leaking bottles on top.
    Methane is also self-ignitable from 580C, and burns (within the 4-16% ratio) from 0-540C, the widest burning range of any vehicle fuel...


    The methane gas doesn't explode per se - but the violent phase transfer of the compressed liquefied gas into an instant gas cloud
    (some 600 times bigger than its liquid state) makes this a nightmare for any fire fighter: a BLEVE*,
    where the entire tank ruptures and instantly spill out its boiling liquid gas content.
    LBG cryo-tanks is filled at -160C and up to 10 bar. 2,2 cubic metre of LBG equals 1 metric ton, and makes 1320 cu m at atmospheric pressure.
    This would make a spherical gas cloud of 13,6 metre dia, and a burning outer surface of more than 580 sq metres.
    A filling station here has a LBG "26 ton" tank volume of 57,2 cu m apiece, that equals a round cloud of 40 m dia, and a surface area of 5100 sq m.

    The almost spherical gas cloud burns where it contacts the outside air,
    and if you have a "big enuff" cloud you'd get severe skin burns within the 300m radius safety zone.

    This bus had a pretty small gas volume (<0.314 cu m) in comparison, and there was not any tank ruptures,
    merely a comparatively slow emptying of the flasks.
    An instant LBG discharge from these would "only" make a burning ball of 7 m diameter and 160 sq m burning area.

    *Discovery short on what BLEVEs really could be like:



    Swedish emergency procedures for LBG transports (in English): https://www.energigas.se/library/192...on-lng-lbg.pdf


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