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I was curious as to the reason why water or CO2 can't be used to put off a metal fire. The TL;DR is that with a metal fire the high temperatures cause the H2O a

I was curious as to the reason why water or CO2 can't be used to put off a metal fire. The TL;DR is that with a metal fire the high temperatures cause the H2O and CO2 molecules to be unstable enough that the metal can attract the oxygen molecules to fuel the ongoing fire rendering them useless as a fire suppressors. H2O is even worse as once the oxygen is split from the water molecule you are left with hydrogen which will combust and explosion might cause the molten fire to spread further. This doesn't happen with wood burning as the attraction to the oxygen molecules from the carbon being burnt is the same or stronger than the attraction from the CO2 or H2O molecules.

moistbar 6y ago
Do you think pure nitrogen would work in this situation?
- scythe 6y ago
  You'd need tons. It's plausible but I don't think it's practical. Also, magnesium and titanium can burn in pure nitrogen, so it's not a panacea.
- pmiller2 6y ago
  Probably not. Nitrogen is roughly the same density as air. It would just get dispersed into the atmosphere before it could do much, unless you had insane amounts of it.
- jseutter 6y ago
  Nitrogen wouldn't work in this situation. In fact nitrogen and aluminum will burn, forming AlN. Normally this doesn't happen because of Aluminum readily forms a "rust" layer in the presence of oxygen, and there isn't enough heat. Molten aluminum in a pure nitrogen environment wouldn't have that layer, and there likely would be enough heat.
rtrdea 6y ago
Why are you guys saying put off
tshaddox 6y ago
Out of curiosity, what would happen if you quickly submerged the burning metal into a very large body of water?
- dmix 6y ago
  Fire on the metal increases then ‘explosion’ the size of which depends on the metal type and quantity obviously https://youtu.be/tj7S_DNFgEU https://youtu.be/tj7S_DNFgEU Also alkali metals is fun https://youtu.be/I8tOtZKpi04 https://youtu.be/I8tOtZKpi04
- d110af5ccf 6y ago
  > very large It depends on how large, what temperature, and what type of metal. If there's enough latent heat in the quantity of metal to flash boil a significant fraction of the water, you're going to have a bad time. If you're literally dropping it in the ocean on the other hand, then you'll get a brief but impressive geyser and the fire will go out. (Unless this is an alkali metal we're talking about. In that case you'll just get a "vigorous reaction" of a size proportional to the quantity of metal. Ex: https://www.youtube.com/watch?v=cc6W6SptLvU https://www.youtube.com/watch?v=cc6W6SptLvU)
DavidPeiffer 6y ago
Another big concern is the water turning to steam. It expands 1,000x. 2 cubic centimeters of water expanding to a 2 liter bottle worth of steam. My facility had its own quick response fire unit (production employees who went through fire and rescue training), and I believe the company helped fund a ladder truck for the town of ~600 people which is adjacent to a decent metropolitan area. Fast response is vital to minimize danger to people and damage to the facility. Factories have been leveled by water hitting molten aluminum. The Hackaday link below does a great job summarizing the dangers. https://hackaday.com/2020/12/30/water-and-molten-aluminium-is-a-dangerous-combination/ https://hackaday.com/2020/12/30/water-and-molten-aluminium-i... Explosion links: https://youtu.be/sIJmwF1Qs7M https://youtu.be/sIJmwF1Qs7M https://youtu.be/jvddrln900Q https://youtu.be/jvddrln900Q (last ~20 seconds) Source: Used to work at a very large aluminum facility.
- babesh 6y ago
  Aluminum is also used as fuel in solid rocket propellants. https://en.m.wikipedia.org/wiki/Ammonium_perchlorate_composite_propellant https://en.m.wikipedia.org/wiki/Ammonium_perchlorate_composi...
myself248 6y ago
We did this in HS chem class, with a block of dry ice that we cut in half and hollowed out. Then we coiled up some magnesium ribbon so it would perch in the hole, lit it with a MAPP gas torch, and closed the block. The magnesium continued to burn long after any lingering air in the hollow could've been consumed. After a few minutes the magnesium was gone and we opened the block, and there was black carbon dust in the bottom of the hollow. And that introduced the conversation about using the right extinguisher for the job!
sriram_sun 6y ago
> H2O is even worse as once the oxygen is split from the water molecule you are left with hydrogen which will combust and explosion might cause the molten fire to spread even farther Yup, this is why you never douse an oil fire (say in the kitchen) with water. The fire will erupt! Seen it happen live. Fortunately the damage wasn't bad. One third-degree burn.
- sonofhans 6y ago
  A kitchen oil fire is a different effect. They're not hot enough to disassociate water molecules. What happens typically is that the water floats the oil, and the fire, remaining on top of the oil, spreads more rapidly. Another effect is when the fire (and typically, the cooking vessel) are hot enough to vaporize the water. This rapid vaporization spreads oil droplets rapidly, allowing much more of the oil to burn at once. It can appear explosive, even though it's just rapidly-expanding steam spreading fine oil droplets.
  - lanstin 6y ago
    I think "rapidly expanding and exothermic" is equivalent to "explosive" at least functionally.
    - SAI_Peregrinus 6y ago
      I'd agree that it's explosive. I suspect they were trying to make a distinction between a detonation and a deflagration. A detonation is an explosion with a supersonic shock wave. A deflagration is an explosion without such a shock wave. An oil fire getting water dumped on it is a deflagration, but almost certainly not a detonation. A metal fire getting water dumped on it can result in a detonation. Detonations are vastly more destructive in general than deflagrations.
      - sonofhans 6y ago
        Exactly that. Thank you. You know better words for it than I do :)

moistbar 6y ago

Do you think pure nitrogen would work in this situation?

scythe 6y ago
You'd need tons. It's plausible but I don't think it's practical. Also, magnesium and titanium can burn in pure nitrogen, so it's not a panacea.
pmiller2 6y ago
Probably not. Nitrogen is roughly the same density as air. It would just get dispersed into the atmosphere before it could do much, unless you had insane amounts of it.
jseutter 6y ago
Nitrogen wouldn't work in this situation. In fact nitrogen and aluminum will burn, forming AlN. Normally this doesn't happen because of Aluminum readily forms a "rust" layer in the presence of oxygen, and there isn't enough heat. Molten aluminum in a pure nitrogen environment wouldn't have that layer, and there likely would be enough heat.

rtrdea 6y ago

Why are you guys saying put off

tshaddox 6y ago

Out of curiosity, what would happen if you quickly submerged the burning metal into a very large body of water?

dmix 6y ago
Fire on the metal increases then ‘explosion’ the size of which depends on the metal type and quantity obviously https://youtu.be/tj7S_DNFgEU https://youtu.be/tj7S_DNFgEU Also alkali metals is fun https://youtu.be/I8tOtZKpi04 https://youtu.be/I8tOtZKpi04
d110af5ccf 6y ago
> very large It depends on how large, what temperature, and what type of metal. If there's enough latent heat in the quantity of metal to flash boil a significant fraction of the water, you're going to have a bad time. If you're literally dropping it in the ocean on the other hand, then you'll get a brief but impressive geyser and the fire will go out. (Unless this is an alkali metal we're talking about. In that case you'll just get a "vigorous reaction" of a size proportional to the quantity of metal. Ex: https://www.youtube.com/watch?v=cc6W6SptLvU https://www.youtube.com/watch?v=cc6W6SptLvU)

DavidPeiffer 6y ago

Another big concern is the water turning to steam. It expands 1,000x. 2 cubic centimeters of water expanding to a 2 liter bottle worth of steam. My facility had its own quick response fire unit (production employees who went through fire and rescue training), and I believe the company helped fund a ladder truck for the town of ~600 people which is adjacent to a decent metropolitan area. Fast response is vital to minimize danger to people and damage to the facility. Factories have been leveled by water hitting molten aluminum. The Hackaday link below does a great job summarizing the dangers. https://hackaday.com/2020/12/30/water-and-molten-aluminium-is-a-dangerous-combination/ https://hackaday.com/2020/12/30/water-and-molten-aluminium-i... Explosion links: https://youtu.be/sIJmwF1Qs7M https://youtu.be/sIJmwF1Qs7M https://youtu.be/jvddrln900Q https://youtu.be/jvddrln900Q (last ~20 seconds) Source: Used to work at a very large aluminum facility.

babesh 6y ago
Aluminum is also used as fuel in solid rocket propellants. https://en.m.wikipedia.org/wiki/Ammonium_perchlorate_composite_propellant https://en.m.wikipedia.org/wiki/Ammonium_perchlorate_composi...

myself248 6y ago

We did this in HS chem class, with a block of dry ice that we cut in half and hollowed out. Then we coiled up some magnesium ribbon so it would perch in the hole, lit it with a MAPP gas torch, and closed the block. The magnesium continued to burn long after any lingering air in the hollow could've been consumed. After a few minutes the magnesium was gone and we opened the block, and there was black carbon dust in the bottom of the hollow. And that introduced the conversation about using the right extinguisher for the job!

sriram_sun 6y ago

> H2O is even worse as once the oxygen is split from the water molecule you are left with hydrogen which will combust and explosion might cause the molten fire to spread even farther Yup, this is why you never douse an oil fire (say in the kitchen) with water. The fire will erupt! Seen it happen live. Fortunately the damage wasn't bad. One third-degree burn.

sonofhans 6y ago
A kitchen oil fire is a different effect. They're not hot enough to disassociate water molecules. What happens typically is that the water floats the oil, and the fire, remaining on top of the oil, spreads more rapidly. Another effect is when the fire (and typically, the cooking vessel) are hot enough to vaporize the water. This rapid vaporization spreads oil droplets rapidly, allowing much more of the oil to burn at once. It can appear explosive, even though it's just rapidly-expanding steam spreading fine oil droplets.
- lanstin 6y ago
  I think "rapidly expanding and exothermic" is equivalent to "explosive" at least functionally.
  - SAI_Peregrinus 6y ago
    I'd agree that it's explosive. I suspect they were trying to make a distinction between a detonation and a deflagration. A detonation is an explosion with a supersonic shock wave. A deflagration is an explosion without such a shock wave. An oil fire getting water dumped on it is a deflagration, but almost certainly not a detonation. A metal fire getting water dumped on it can result in a detonation. Detonations are vastly more destructive in general than deflagrations.
    - sonofhans 6y ago
      Exactly that. Thank you. You know better words for it than I do :)