Tuesday 6 August 2013

Fatberg follies

There's a great fat story going viral across the blogosphere today about a 15 ton 'fatberg' that almost completely filled a sewer in Kingston in suburban West London. I get my feeds from Metafilter where it was claimed that 15 tons of lard was the size of a double-decker bus.  They probably read the Daily Mirror who are likely to big up a silly-season story like this, so I turned to the broadsheet The Independent, whence I gleaned that the mass of 'lard' and wet-wipes a) weighed 15 tons b) was the size of a bus c) was found in a sewer 70cm x 48cm in section, that was reduced to 5% of its capacity.

Does this make sense?  Wolfram alpha reports the density of lard as 0.87g/ml or about 90% that of water.  But why keep a dog when you can bark youself?: The 454g=1lb block of butter in our fridge is 13cm x 6cm x 6cm = 468ml which says that butter is almost the same (97%) density as water.  Maybe it's the added salt that ups the density?  We'll call it 0.9g/ml.

Metafilter's "double-decker" bus is 10m x 4.4m x 2.4m = 105cu.m.  The Indo's "regular" bus is not so tall: 10m x 2.4m x 2.4m = 58cu.m.  Whereas the volume of the fatberg (if lard) is only 16cu.m.  Say a 4m x 2m x 2m minibus?  Doesn't sound as exciting as a double-decker does it?  And as sewers are by definition long (must put distance between ourselves and our waste) and relatively thin, any sort of bus is a rather crap metaphor, isn't it? 70cm x 48cm is as near as dammit 1/3 sq.m.  So I surmise that the ribbon of lard was about 50m long.

Has anything useful come out of this "analysis"?  Sure.  If you filled a double decker bus with beer and could get it on board it would satisfy the liquid refreshment requirements of the crew of the Golden Hind for the first year of her round the world voyage in 1577.

Oh yes, and don't pour hot fat down the kitchen sink.  And "flushable" wet-wipes are not biodegradable in any practical sense.

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