underground said:
Shotlighter, are you 'Nigel, Kidsgrove'?
And, the possibility that 'they didn't believe their gas detectors'.... you'll have to forgive me again - do they give 'false positives'? if so how do you know when to believe them? Just before falling unconcious?
Indeed I am. I've known this site for nearly 50 yrs since when my grandad used to hold me up to watch trains emerging!
I've not been in for several years, but as I say the blackdamp from one level in particular is hideous & the sudden drop in pressure must of dragged it into the main tunnel. I really can't understand why a stopping wasn't put on it while the tunnel was still in use. The coal working (Bread & Herring or Ashwood?) must have stopped work in the early 1900s. It's a popular place for kids to go for an "adventure" but luckily the level is easily missed, as it's in the back of a manhole. Otherwise it could easily have been the site of a tragedy.
As for gas detectors, all sensors can give false +ves in the presence of other certain other gases/vapours (not usually a situation encountered in our application) but with age just stop working, so give no response at all. The exception to this is the O2 sensor (presumably the one that alarmed), which will become less sensitive to O2 as it ages & will therefore give a false -ve, which in this case is the alarm condition. This is why it is so vital to have gas detectors regularly calibrated.
Hope this makes sense, as it's late on Fri night!
I will make no comment on the training of the maintenance team, or the quality of any information that may have been given them prior to them entering the tunnel, as of course I was not privy to it.
Sorry, to answer your last point, you have to believe them - if the alarm goes goes off, you go out! If you stay it's at your own risk.