If the freedom of speech is taken away then dumb and silent we may be led, like sheep to the slaughter.

- George Washington

Sunday, 17 October 2010

Unintended Consequences

I remember learning about the Davy Lamp at school. Twice, in fact. Once in primary school, where we learned about wonderful inventions that benefited the human race, and once in secondary school, as part of a physics lesson about oxygen and flame propagation.

The Davy Lamp was invented in 1815 by Sir Humphry Davy. In 1812, there was an explosion of flammable gas in a mine at Felling, near Newcastle-upon-Tyne. A miner's candle ignited a pocket of methane, which caused an explosion in the coal dust present in the mine's atmosphere, which blasted through the galleries and erupted through the main shaft to the surface. 91 miners lost their lives. One of the things most feared by miners in the early days was 'damp' - gases in the air of the mine which were both undetectable and deadly. The main two were firedamp, which was basically methane and was highly flammable, and blackdamp, which was mostly carbon dioxide and was suffocating.

Davy was a chemist (he discovered both chlorine and iodine), but was also an amateur inventor. He started a series of experiments to see if a naked light could be shrouded so that oxygen could still reach the flame, but the flame could not ignite any surrounding gases. The lamp which bears his name had a naked flame over a reservoir of vegetable oil, and the flame was contained in a gauze tube. The holes in the gauze were big enough to let in oxygen and methane, but would not let the flame propagate outwards.

The lamp worked very well. In the presence of methane, the flame would rise up in the lamp and develop a blue tinge. This would alert the miners to the presence of firedamp and allow them to avoid it or take corrective action, and also would give them light to work without the risk of explosion. Placed on the floor, where blackdamp accumulates, the flame would go out if the oxygen level went below 17%, which indicates the presence of Co2 but will still support life, allowing the miners to escape before the atmosphere became deadly. Although fragile, the lamp worked well and should have been a major factor in improving mine safety.

Except it wasn't.

After the introduction of the Davy Lamp, mine accidents increased. The lamp (which had to be bought by the miners themselves from the same company stores where they used to buy their over-priced candles) allowed mining in mines that had previously been closed for safety reasons. Also, methane itself is not toxic, so the presence of the Davy Lamp allowed mining to continue in places where firedamp was present. One spark from a metal pick or a hobnail, or one strand of the gauze rusting away from the shroud on the lamp, or a clumsy fall allowing the lamp to spill onto the floor - and another explosion occurred.

Mine explosions following the introduction of the Davy Lamp (numbers killed in brackets):
  • Oaks Colliery 1866 (388)
  • Wood Pit, Haydock 1878 (189+)
  • Trimdon Grange 1882 (69)
  • Hulton Colliery 1910 (344)
Davy saw his invention as a contribution to the saving of human life. The mine owners saw it as an opportunity to make more money by pushing mining operations into areas that previously were too unsafe. The net effect was to kill more people than before.


  1. Talking about unintended consequences I read that the introduction of steel helmets for our troops during WW1 actually resulted in more head injuries being treated.
    Previously the troops had just died when hit in the head and there was no treatment required.

  2. Each advance creates a new problem. Seat belts for cars comes to mind: fewer drivers and passengers killed, but more pedestrians and cyclists.

  3. Boxing gloves.

    Bare-knuckle fighters tended to be careful where they punched, and often avoided the face and head because they'd break their own knuckles.

    Several studies since the introduction of gloves have shown they cause fewer superficial injuries but a far greater incidence of serious brain damage, as fights can now last longer and head punches are much more common.

  4. Good point. That never occurred to me, but it makes perfect sense. So where the professional fighter used to have a scarred and beaten face, he now has a drool and can't find his words, but his cheeks are smooth and his chin straight. Some trade.

  5. An early example of the Peltzman effect?


  6. I guess it is. I know that theory as 'risk compensation', but it's the same idea. I was amazed to learn that the introduction of ABS on almost all cars has not had a significant effect on accident rates - the reason being, of course, is that people with ABS drive faster and leave less space because they 'know' the brakes will save them. And cars drive closer to cyclists who are wearing a helmet. Actually, it's not quite the same. All these effects are behavioural - natural human reactions to changes in perceived risk level. The mining accident rate was, I believe, sheer naked exploitation of a new invention, allowing mine owners to drive their workers into more dangerous places.

  7. Re: unintended consequences, I think it was in Australia, but when they whacked the tax up by huge amounts on alcopops in an attempt to curb teenage drinking, it actually led to more deaths from alcohol poisoning as teenagers resorted to making their own cheaper versions.

  8. Same in America under Prohibitioon, I think. Illegal stills producing home-made liquor caused more alcohol-related deaaths and disability than the legal drink that they banned. These things never work as they are supposed to. Human nature is too tricky for that.

  9. If you have not come across this stuff before there is lots to read on John Adams website http://john-adams.co.uk/

    Get more people thinking and the stupid use of daytime headlights by motorcyclists might start to be questioned.....

  10. "Illegal stills producing home-made liquor caused more alcohol-related deaaths and disability than the legal drink that they banned. These things never work as they are supposed to."

    Same as the problems we get from banning recreational drugs today.....

  11. Voyager 19:44

    "Get more people thinking and the stupid use of daytime headlights by motorcyclists might start to be questioned....."

    I take it you're not a biker, attempting self-preservation from some car drivers who don't 'mirror, signal' before manoeuvering?

  12. @Voyager: Thanks for the link to John Adams. I shall have to read him more often. I agree with pretty much everything I have read there so far.

  13. Risk homeostasis theory is not without its crtics.


  14. I heard a senior policeman muse that the most effective way to promote safe driving would be to remove air bags from the centre of steering wheels and replace them with 12 inch metal spikes. Cruel but fair.


  15. @Jim: I've read that essay, and while he makes some good points, overall I am not convinced. Too many straw men - he is imputing to the risk compensation/homeostasis theory a claim to statistical accuracy that I don't recognise. I haven't read Wilde so I don't know if that is what he claims, but I see it as a general tendency, rather then a scientific and measurable phenomenon. Certainly, if I ride in jeans rather than leathers or armoured textiles, I don't ride as fast, and I corner much more gently, as I am more aware of the vulnerability of my sticky-out bits. The theory certainly applies to my own behaviour. However, and interesting read, and thanks for the link.

    @Derf: I've heard that before, too. It makes the point quite well, I think.

  16. @Joe - he is indeed a full time motorcyclist, not that he needs me to defend him. As for daytime running lights, there's considerable evidence they do more harm than good (check out the abject failure in Austria a few years back, for a good example). Personally, if my current bike allows it, I always run with lights off in daylight. If it doesn't, I put up with them being on but have absolutely no expectation it makes a blind bit of difference to other motorists' perceptions or actions. Except on bumpy roads when I half-expect them to pull out, after mistaking front-end travel for a friendly flash to do so. There is no safety in assuming other road users might have seen you.

    @Rich - I believe that the boxing gloves idea was actually down to the promoters, who wanted to give the public longer and more visual spectacles regardless of the risk to their contestants.

  17. Hard-wired headlight on bikes: I'm a bit 50/50 on this. Under normal circumstances, I try to ride as if I am invisible, so the presence or absence of a headlight shouldn't make any difference to me. I'll ride as if they *haven't* seen me, whatever. I do find a fixed light useful on dual carriageways, though. Cars tend to see you in their mirrors and move over much quicker, and on roads where people are moving fast, having people aware you are there early is a good thing. The Bonnie has a hardwired headlight, and I am fine with that, but the Yam hasn't, and I don't turn it on deliberately unless the lighting conditions demand it.

    Of course, if the plans for headlights-on for ALL vehicles come to pass, than any small advantage bikers have will be gone.

    Boxing gloves - hehe, same as the Davy Lamp thing, really. Profit before safety - a categorical no-no for anyone involved in the H&S business. Even for a happy-with-risk-as-long-as-it-is-managed person like me.

  18. Does anyone have a viable solution to the "Sorry-mate-I-didn't-see-you" problem? Anger is justified, but doesn't actually help; and I see the point about lights and unintended consequences.
    Riders always assuming that they haven't been seen, that's a bit unrealistic? I give bikers a nod when I'm waiting at a junction, so they know that I've seen em. That makes their life a little easier, but doesn't solve the big problem. And what about the one that I won't see, one day?
    I read once that sailors are aware that anything on a collision course doesn't move relative to the background. That sounds a bit complicated, but it's important.

    Car drivers- When coming out of a junction, don't just rotate your head. Move it about a foot, side to side. This gives your stereo vision an 18 inch baseline, instead of 6 inch. If you don't follow that explanation, just do it. It works. Make it a habit. Every little helps. Bikers don't want to die, and drivers don't want to kill.

  19. Certainly as a car driver I wag my head around when looking right before pulling out. with face close to the glass so I can be seen clearly.
    Don't know why, just do :-)

  20. @Zaphod- you make some good points, which I have responded to here. Thank you for your input.

  21. @George - thank you for being a good driver! If only everyone were as thoughful. I do this when driving a car, if only for self-preservation.

  22. Joe Public - "I take it you're not a biker, attempting self-preservation from some car drivers who don't 'mirror, signal' before manoeuvering?"

    No. I've only been riding for the past 30 odd years but one thing I've learned is that the use of daytime headlights is asinine method of 'self-preservation'


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