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I just saw a documentary where they investigated lakes inside of glaciers. They rapelled in big crevasses and even dived in those sometimes huge water reservoirs.

The scientist had a regular looking headlamp but on top of it there seemed to be an open flame. What could be the purpose of this tool and how does it work?

Made a picture of that headlamp:

enter image description here

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  • Name of the film?
    – Joe Manlove
    Commented Jan 25, 2015 at 16:46
  • Diving is common in deep caves in order to pass syphons (sumps) and access more areas within the cave network.
    – ShemSeger
    Commented Jan 26, 2015 at 16:19

2 Answers 2

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I would guess it's a carbide lamp as it was in former times used by mining workers and is still used in speleology (caving) sometimes.

The basic working principle is a box with carbide and a water reservoir from which water slowly drips onto the carbide. Carbide and water chemically react and form acetylene gas which is guided through a hose to a small nozzle where it is burned. The flame is in front of a metallic mirror to concentrate the light.

So why is this (still) used? The advantage of this setup are

  • Less problems with cold temperatures: Batteries tend to provide significantly less power when they get cold. As in caves and glaciers the temperatures are at best something like 10°C, this can be some serious problem if one has to work there for longer.
  • Better energy density (energy per weight ratio): Compared to batteries carbide provides more energy per weight and in many glacier or caving spots water – the second ingredient – can be obtained nearly everywhere, so one has to carry only the amount of carbide needed.
  • No electricity problems: there are no electric circuits that could be short cut when water enters the lamp system.

Possibly they did wear those lamps just for the documentary to give it some nostalgic touch, but there are situations where such lamps are at least not worse than battery powered ones.

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    Carbide seems like the most obvious answer, but using it that close to a modern climbing line is quite dangerous. Rappelling is one of the situations where a carbide is quite a bit more dangerous than a headlamp.
    – Joe Manlove
    Commented Jan 25, 2015 at 16:45
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    @EverythingRightPlace - Long expeditions are where carbide lamps excel, they significantly outlast any battery. Like Benedikt said, they have better energy density, which means they have a longer burn time for less weight than batteries, they also have a better illumination area (they light everything, not just a spot). Check out this documentary: Krubera-Voronya They explore the deepest cave in the world, one where they have to descend to multiple base camps and spend days in a row underground. They explain all the gear, including carbide lamps.
    – ShemSeger
    Commented Jan 26, 2015 at 16:16
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    @JoeManlove - It's no more dangerous than rappelling with crampons, both have the potential to cut or damage the rope, you simply need to be mindful of where your ropes are. If you're burning through your lifeline then it's 100% operator error. There's a reason why he's also wearing a Petzl Fixo Duo in addition to the carbide lamp, in situations where it's hard to keep his head away from the rope he can easily switch to LED light.
    – ShemSeger
    Commented Jan 26, 2015 at 16:30
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    @ShemSeger - It's not rope damage I'm worried about, it's where the rope is damaged. You can't cut the rope above the device with a crampon but you can definitely melt it with a carbide. It's certainly not suicidal, but it is dangerous.
    – Joe Manlove
    Commented Jan 26, 2015 at 16:58
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    @JoeManlove - If you step on the rope with a crampon while rappelling, then that cut piece of rope is the very next thing going through your rappel device. You make the cut below your device, but in less than one second it's going to be above you, that's if it makes it all the way through your device... Rappelling, caving, and alpinism are all dangerous to begin with. People have been rappelling into caves with carbide lamps for many years, just like every other outdoors sport, people must learn to use their equipment right and avoid mistakes which lead to accidents.
    – ShemSeger
    Commented Jan 26, 2015 at 17:39
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What you're looking at is a carbide lamp, and it looks to be a Petzl Aceto. What you can't see in this photo is the generator, which is a round canister with two parts. The upper part contains water, which drips into the lower part containing small lumps of calcium carbide. The reaction releases acetylene gas, which travels via a tube to the actual lamp.

Compared with electric lamps they have a few advantages:

  • Much more robust and resistant to water ingress (water is no harm at all)
  • No need to recharge batteries every day (it's easy to carry enough carbide for a week-long trip if necessary)
  • Continuously-variable brightness (and peak brightness greater than halogen bulbs)
  • Performs better in the cold
  • Actually generates warmth (both the generator and the flame) - useful in emergency situations

And a few disadvantages:

  • A tendency to extinguish in waterfalls
  • Leaves soot marks when waiting around
  • Spent carbide needs disposing of properly

Over the last couple of decades, electric lamps have improved greatly with new technologies (Li-ion batteries and LEDs) and better build quality that the advantages aren't as great as they used to be. And some cave systems have restrictions prohibiting the use of carbide (generally for conservation reasons, due to a history of indiscriminate dumping of spent rocks). But carbide still comes into its own on long expeditions, and as the photo shows, it's common to have both carbide and electric on the helmet so that each can be used where it's the best tool for the conditions.

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  • Could you add a Model no. oder link to the vendor for that specific lamp? That would make this answer even better...
    – fgysin
    Commented Mar 10, 2021 at 6:13
  • @fgysin, I've done my best (I don't actually own one, just caved with a few who do).
    – Toby Speight
    Commented Mar 10, 2021 at 7:42
  • The Carbide lamp is a Petzl Aceto. Petzl no longer show that item as available on their website as carbide lamps have been superseded by LED electric lights in caving. I used one extensively until the late 2000's when LEDs became superior. The electric light shown beneath is a Petzl Duo and that again is no longer shown on Petzl's website although a different headlamp with the same name is.
    – Paul Lydon
    Commented Mar 19, 2021 at 10:45

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