King's Cross

A genuinely uneventful day's commuting for me today. Although, I was on the railway in time to get a West Ruislip through train from ROV (long-ish, cold wait at WOO on the way back though). At King's cross, I did happen to notice, though, that the Uxbrdige train behind my Circle line C stock was calling at all stations - as it should! :P. Also, the train behind that was a semi-fast Amersham service - not terrifically interesting, but I like to keep an eye out for the service patterns (e.g. fast and semi-fast trains) on the Met, which I find fairly interesting and about which there isn't very much detailed information I've been able to find. As a result of spotting this, I spent quite a while thinking about Metropolitan line services when I should have been contributing to the class...Oh well, at least I've got my priorities right :P

On the way back from King's Cross I also noticed some flowers around the memorial to the fire there. The 26th anniversary of that dreadful event was yesterday, which I assume was the reason behind the flowers. A fire began under a Piccadilly line escalator at around 19:30 in the evening. These aged escalators were built with wooden steps and the area beneath the escalator was filthy with years of grease and fibrous material having built up. It is believed that the fire was begun by a discarded match, which had fallen down the side of the steps - charred wood on a section of skirting indicated that similar fires had occurred before, but they had burnt out. Although smoking had been banned across the network in response to a fire at OXO (Oxford Circus) - a ban which is now much more rigidly enforced - it was still common for cigarettes to be lit on the way out of stations.

The fire was reported to staff who investigated and the fire brigade was called. Because of the location of the fire, underneath the escalator, the fire could not be fought without the assistance of the fire brigade and it was decided to evacuate the station at 19:39. Presently, the fire brigade arrived and assessed the fire, which they found to be about the size of a cardboard box. As they prepared to put the fire out, it flashed over at 19:45. A flashover is an extremely dangerous event; the resulting jet of flames filled the ticket hall and cost 31 people their lives. Many people were trapped in the station and had to be evacuated by trains passing through the station. It took more than 150 firefighters until 01:46 to put the fire out completely.

Since then, most of the old wooden escalators have been replaced (although I believe there is still one at Greenford, also one of few places on the Underground where passengers need to travel up an escalator from street level to get to the trains.) Smoking is also more strongly prohibited on the tube and staff are better trained to deal with fires.

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For those who might be interested, the main effect in the case of the King's Cross fire was the Trench effect - an effect which was not well known before. When the grease and fibrous materials involved in this fire burn, they release hot smoke. The heat was well-contained by the escalator, although there was also a good supply of oxygen. This smoke heated the wood of the escalator, which released flammable gases (in this case predominantly methane) by a process known as pyrolysis. As these hot gases built up, the temperature eventually rose to the point at which the now plentiful gases auto-ignited. This is called a flashover. It is extremely dangerous, because a seemingly small fire which (as it seems was the case in the King's cross fire) can seem to be of relatively minor concern (which can lead to complacency) can result in a sudden and deadly fireball. The fireball which resulted from this flashover "climbed up" the sides of the escalator by a process known as the Coandă effect. The combination of a flashover and the Coandă effect is the trench effect seen at King's cross. The fire resulting from the flashover, having "climbed up" the sides of the escalator was ejected into the ticket hall, resulting in the many deaths and 100 people injured, 19 seriously.