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Comment by zaarn | Hacker News Reader

Aluminium burns too, just harder to get going. Almost all the metals can be coaxed into burning in various ways, all metal fires are an absolute disaster when they happen.

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Can you point to an aluminium fire that wasn't based on the aluminium being powdered, and where there were no fire enhancers (O2-enriched atmosphere, oxidizers like permanganate) present, and that sustained itself? (Because that's the conditions ars was talking about. Maybe if in ars' case the aluminium part was mostly liquid due to the short before it started burning that would explain it, but then they didn't describe it that way.)

Google "aluminum foundry fire", there is plenty of examples.

It does not burn easily but once aluminum has ignited it can continue to burn under normal atmospheric conditions, especially if it begins to melt and boil.

Yes, what I've found indicates that aluminium burns when it boils, which is at 3073 °C, which doesn't happen in normal fires (house, car, forest fires), which is why it's safe in normal fires. It is melting at 660°C, at which point it doesn't burn unless perhaps if finely distributed by way of pressured air bursts or similar.

Sparks are hotter than 3073°C, but usually they don't ignite aluminium either--there not being enough aluminium vapour to sustain the reaction.

I've done what you said and googled, but have not found a case that indicates non-dust aluminium was burning.

https://www.readingeagle.com/2022/04/19/reamstown-fire-alumi... : Looks like a dust fire. Easily extinguished. Does not sound like any solid or molten aluminium was burning.

https://dailyvoice.com/pennsylvania/lancaster/news/fire-brea... "The fire is believed to have started in the finishing area, where workers grind the aluminum castings"

https://www.fox43.com/article/news/local/fire-aluminum-found... no details

https://lancasteronline.com/news/local/fire-damages-east-coc... "not sure what caused the fire, which began near – but not in – a dust collection system at the plant."

https://www.abc4.com/news/fire-causes-400k-in-damages-to-ogd... "The fire was contained within an hour after crews arrived. No one was injured. Damages were mainly to the machinery and the foundry metal fabrication plant structure."

https://mix999fm.iheart.com/featured/murphy-sam-jodi/content...

https://news.yahoo.com/fire-boose-aluminum-foundry-lancaster... (Video shows normal flames, not from a metal fire.)

What types of sparks are that hot?

It was very thin metal, it was the shell of a cheap light bulb socket, and it was enhanced by the electrical short - I don't remember the circuit breaker tripping.

It burned until there was no more silver color metal left, leaving just the copper wire leads. I assume it was aluminum, I think steel would be harder to burn.

I do remember unplugging it during the fire, but it didn't take very long to burn, so I might have done it after it was over.

Again, from all sources I've ever seen, you can't ignite aluminium blocks and have a sustained fire, whereas you can with magnesium. If the aluminium is liquid then perhaps by spraying it around because of the spark it would give the effect you describe, but it sounds dubious that it melted so quickly in a large enough amount, and it seems somewhat unlikely to me that once it started the sprayed liquid aluminium would stay close enough to melt and burn the remainder, too. When you see pictures of large arc flashes, a lot of metal is sprayed from the location of the arc and then burns, but it burns flying away so it cannot sustain the reaction; the cause of the metal burning and flying away is the arc. In your case you didn't have enough electric power to get such a strong arc (the 10-15 A you get from house hold power before tripping the fuse is not that much), so the energy to sustain burning up the remainder of the metal must have come from the metal fire itself. That is definitely possible with magnesium, but from all I've seen it is not with aluminium.

Magnesium can be set alight even when multiple cm in thickness [1], and lighting up thin strips is much more spectacular[2]. You can hold aluminium foil to a blow torch, what happens is it will melt and oxidize, but not produce any flame or light whatsoever[2]. If aluminium foil doesn't do it, I don't see how a thicker sheet would do it. And all I've found confirms this. (BTW steel wool however does burn continuously. But I agree that a steel lamp base burning this way doesn't look feasible, either.)

[1] e.g. video on https://en.wikipedia.org/wiki/Magnesium [2] source: own experiments, and there will be videos from others

Since you say that it was thin, it must have been an alloy in either case. It seems Magnesium alloys need to be cast. I've got a laptop with a magnesium base which looks like sheet metal from the outside but when you open it up, on the inside it has all sorts of structures coming out of the "sheet", clearly confirming it was cast. I've never seen aluminium parts made that way, aluminium cast parts seem to always be relatively thick, not like sheet metal. Aluminium can be pressed, however (think beer cans), but then it doesn't have a fancy structure. I'm not a specialist in these matters in any way, but maybe this might give some further ideas.

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