The Lamp That Saved Coal Miners' Lives | Hacker News Reader

The Lamp That Saved Coal Miners' Lives

mentalfloss.com

16 pointsHooke8 comments

It is sad reading the impact section at https://en.wikipedia.org/wiki/Davy_lamp

"The introduction of the Davy lamp led to an increase in mine accidents, as the lamp encouraged the working of mines and parts of mines that had previously been closed for safety reasons."

and

"Another reason for the increase in accidents was the unreliability of the lamps themselves. The bare gauze was easily damaged, and once just a single wire broke or rusted away, the lamp became unsafe. Even when new and clean, illumination from the safety lamps was very poor, and the problem was not fully resolved until electric lamps became widely available in the late 19th century."

Seems like it wasn't as successful as it is made out to be in this article.

An extreme example of https://en.wikipedia.org/wiki/Risk_compensation. I was somewhat disturbed when I first learned that this is what actually happens.

I don't understand how a methane/oxygen reaction, once ignited, cannot travel through a metal cage… I'm sure it works but the "absorb the heat that caused the explosions" explanation doesn't make sense to me. Does anyone know in more detail how this works?

more details here:

https://en.wikipedia.org/wiki/Flame_arrester

https://en.wikipedia.org/wiki/Davy_lamp

https://www.youtube.com/watch?v=u-GeraWUP6E

The wire mesh drops the temperature below ignition temperature and also drops the pressure. Since the outer air remains relatively cool, the mesh presumably continues to shed some heat through contact with the outside air, and so doesn't itself reach the ignition temperature on the outside. Maybe sort of like how you can hold a flame to a paper cup full of water and even though the paper is dry on the outside, it won't catch.

I suspect that it acts as a sort of diffuser. Any source of ignition within the grill has to pass through it to induce an explosion. The mesh allows the heat to spread out more evenly, making the temperature at any one point on the mesh lower (the energy is still there, but likely isn't concentrated enough to cause ignition). As a result, with respect to the flame, the little burning particles from the wick need to get through the grill to ignite the gasses outside the cage, and the fine mesh makes that less likely too (I think microscopic burning embers are surprisingly likely to bump into the mesh, since fine wires have high drag aerodynamics and so the air will cause the gases to linger near the mesh; a finer, denser wire mesh just amplifies the effect that way while still letting out much of the light).

I bet it's not failsafe, but it undoubtedly is a vast improvement on an open flame.

Sir Humphry Davy (the inventor of the lamp) had an awesome honeymoon: http://blog.jgc.org/2008/09/ultimate-nerd-honeymoon.html

The chemist received a medal from the Royal Society and was made a baronet; he even “designed his own coat of arms, showing the safety lamp encircled with a Latin motto which announced: ‘I Built The Light Which Brings Safety.’”

Excellent!

From the article on Wikipedia:

"The introduction of the Davy lamp led to an increase in mine accidents, as the lamp encouraged the working of mines and parts of mines that had previously been closed for safety reasons"

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