Wednesday, January 19, 2005

Barge Fire Update

The 10 o’clock news reports indicate that the cause of the barge fire is likely to be in the boiler system. Probably it would actually be the expansion tank. The system is analogous to a hot water home heating system. There is a “boiler”, several radiators (heat exchangers), an expansion tank and the interconnecting piping. Instead of water, the system uses an organic heat transfer fluid such as Dowtherm A. The expansion tank is either vented to atmosphere or has a nitrogen inerting blanketing system. My guess is this barge would just have a vent. If the vent got clogged, it would allow pressure to build up until the tank ruptured spreading hot oil everywhere and ripping out the piping. A spark from a newly exposed wire would set off the fire. Having ruptured the hull to piping welds, the contents of the tanks would be exposed to air and their contents could add fuel to the fire. The heat of the fire would weaken the steel of the deck, transferring the stress exclusively to the keel. This would result in the stern sagging (a process known as hogging) until the keel snapped. Such a scenario seems to be consistent with the facts.

Since the bow section is still secured to the dock, it would seem most expedient to cut any remaining attachment in the keel area, so that it could be pulled free. That leaves just the stern section. Using what salvors call “beach gear” the stern could be dragged out of the channel. Then cut into manageable sections and lifted out of the channel by crane. Of course, if they want to make a show out of it, they could use explosives to pound the wreck down into the bottom. This technique was pioneered in 1942 by Merritt-Chapman and Scott in clearing the wreck of the SS Stephan R. Jones from the Cape Cod Canal.

This would have been an interesting test case for using carbon dioxide to suppress the fire. One technique would be to spray liquid carbon dioxide in a process that would create dry ice “snow”. Basically, it would be like a snow making machine at a ski resort. The other would be to mix water and carbon dioxide into a “seltzer water” mixture and spray that on the fire working from the windward side in. This would create a wall of carbon dioxide gas that would displace any oxygen thereby suffocating the fire. (See a further discussion in previous posts regarding the LaSalle Bank high rise fire).


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