Wednesday, 6 March 2013

Interview in BBC Material World: coal self-heating

Last Thursday, between my two lectures on M2 Heat Transfer and M4 Combustion, I was interviewed by Quentin Cooper for BBC Radio 4 Material World.

You can hear the programme in the BBC podcast (we start from 14 min). A very nice expert on petrology was also invited to talk, Tony Milodowski, from the British Geological Survey.

Quentin was interested in learning about the science behind the recent news of a large fire in the coal mine of Daw Hill, the last remaining pit in Warwickshire, England. The first reports coming out say the initiating event was spontaneous ignition of coal. The fire developed quickly and a full evacuation of the mine was ordered. I was quick to mention that the longest continuously burning fire on Earth is The Burning Mountain in Australia, now a National Park, a coal seam that has been smouldering for more than 6,000 years. I always add at this point that at least the British cannot be flame for starting it.

Artistic illustration by E Burns 2008 of how I see that a smouldering coal fire could develop underground of a mine. The figure illustrate the spread of smouldering along the coalface and surface cracks of the seam, off gassing on the surfaces, subsidence and suppression attempts. I used this figure in the book chapter "Smoldering Combustion Phenomena and Coal Fires"
I talked about the phenomena of self-heating in a previous post after the biomass fire in Tilbury Power Plant. It refers to the tendency of certain materials, like biomass pellets and coal, to spontaneously heat up and smoulder starting from ambient temperatures. Self-heating can result in a spreading fire without intervention of any external ignition source. The topic is one of my fields of expertise. The problem can go undetected until the accident takes places.

NOTE: A substantial body of literature, not centered on combustion science, uses the term "spontaneous combustion" when referring to fires that started as self-heating. In rigorous terms, this is incorrect and misses the point of the key phenomena at play. The spontaneous process here is the heating that acts as ignition of a combustion reaction and leads to a fire; the combustion is not less spontaneous or fundamentally different than other smouldering or flaming phenomena.
Smouldering combustion in glowing coal embers, from Wikipedia.
The interview took place in the studios of the BBC, and one of the highlights of my day was to enjoy the stunning building that Broadcasting House is. It is pretty and smart from the outside (the inward curved entry, making a C shape, is marvelous) and comfortable and interesting in the inside (all transparent glass walls and soft lights). While touring the building a bit, I was lucky that one of the BBC Radio 4 staff members mentioned she was choosing the photo illustrating this interview for the podcast website, and I immediately offered my advise. I recommended they use the photo illustrating the term "smoulder" in Wikipedia, a page that I started back in 2006. This photo is superb! and they took my advise.