CNG bus explosion - GIF

[Altair]

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

[Karl_H]

As Alfred Nobel would say "Boom goes the CNG!"

[WorkerB]

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

[clavius]

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/

[jdurand]

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?

[DIYSwede]

This was LBG - "Liquefied BioGas" a k a Liquid Methane, extracted from sewage processing plants in Stockholm.



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 580°C, and burns (within the 4-16% ratio) from 0-540°C, 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 -160°C 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