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Comment by omar_a1 | Hacker News Reader

I think you're not paranoid enough about HF. It doesn't wash off, and is small enough to pass through skin to form insoluble mineral precipitate with calcium in bone and blood, which can result in amputations from dead tissue. It's one of the few acids capable of eating through silicates in glass or rock.

Even at lower concentrations, you still need specialized gloves, apron, and ideally a face shield, in addition to standard PPE. Source: worked with HF for 3 years.

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Agreed.

If I had to choose splashing my arm with a concentrated acid, I would choose sulfuric or nitric acid over HF.

Unlike the other acids that just burn the surface of the skin, HF rapidly penetrated the skin and can mess up your potassium levels. Plus tissue destruction is much deeper.

That's why you keep calcium carbonate salve around. Also you're more vigilant around hf. I've spilled conc sulfuric and nitric acid on my lab coats. HF will never get that close, as safe equipment is in a closed loop but not that complex or byrdensome (it's not like explosives research for example)

There are some idiots that use open air HF for etching. That is a very bad idea.

I should clarify by open in the description I meant valve open. The system was still closed.

Fair enough. You’re using it in a certain way that makes accidental exposure less likely.

I was speaking more generally. It’s not uncommon for labs to handle concentrated HF in a similar manner as other acids - I.e. pouring it into a beaker in a fume hood

Yes this is a mistake but to categorically say that HF is scary and dangerous actually creates, in my opinion, a mindset that is detrimental to operator's of safe HF equipment and also encourages use of more wasteful (e.g. FMOC) techniques which also have tradeoffs (nonsynthesiazbility is more of a problem with FMOC than BOC).

And I was clear that setup matters in my gp.

But who had to carry the jar of HF into the lab and attach it to the closed system?

It's a gas canister, there are extremely secure valves. I've done it myself.

As in, a highly pressurized gas canister? In a container that is presumably 100% impervious to HF corrosion, yet somehow also made out of a material that can withstand those pressures?

How is that safer than neutral-pressure, aqueous HF? I'm perfectly comfortable with bottled HF, to the point that I literally handled it in the dark (light-sensitive samples), but I'd never set foot in the same room as a pressurized HF gas canister. A spilled HF bottle is a major incident, but ultimately straight forward to contain, whereas an HF canister leak would kill off an entire lab.

I've done enough manifold setups and worked with enough gas cylinders to understand that they can leak in all kinds of ways, even with a wealth of experience. As I said initially: you are definitely not paranoid enough about this setup.

Derek covers this in one of his articles. [1]

>It’s sold compressed in metal cylinders, like other gases, but it needs some care in packaging. The stuff is so corrosive that special alloys need to be used, usually ones high in nickel. If you stick an ordinary gas regulator on top of an HF cylinder, you’re in for trouble, and the complete destruction of the regulator is the least of your worries.

>HF has actually been used right out of the cylinder for a long time in Merrifield peptide synthesizers.

[1]: https://blogs.sciencemag.org/pipeline/archives/2004/03/03/th...

This also begs the question of whom exactly has an unobtainium pump that can withstand HF to put it into a cylinder.

I'm just going to say that your ignorance about HF is exactly my point. 100% HF is obtainable commercially in labs and only requires shipping precautions on the order of what you would expect for toxic volatiles.

The irony is that HF is probably worse in lower concentrations partly due to it's dissociative properties, which I won't get into a technical discussion about, and general human stupidity. If you're using 100% HF it's safer, because you're using not very much (we're talking 5-10 mL at a time), the equipment you're using is by nature safer, and you're more vigilant. It's also much easier to mechanically handle 10 mL than 100 (or more mL).

But hey I worked with 100% HF for seven years (BOC protected amino acid synthesis), so what do I know...

Only if we ignore that HF is volatile, meaning that you're dealing with much more (not dissociated) HF evolving from your reagents. Even with a fume hood, you've got much more HF in your face versus a 5% concentration. Calcium gluconate gel will do nothing for HF in your lungs.

I disagree. If something happens with an apparatus, you fucking shut the hood quick. There is very fast positive pressure air blowing in through the sash opening, the apparatus is bolted into the wall, sashed above the nonglass barrier, and there is negative pressure inside the apparatus, so the tendency is to not leak out but leak in.

If you have a 5% aqueous solution most of that HF is still binary undissociated HF, which will leak into the atmosphere so you could very easily unawaredly be breathing it in if you are working with it in any open air situation below the sash line (which is what the tendency is when you're working with aqueous concoctions).

I fail to see how quickly shutting the hood in cases of catastrophic failure address my concerns. When you're dealing with pressure differentials and compressed gasses, explosions and implosions are a very real risk, and shutting the fume hood, even quickly, will not help in the fraction of a second these failures would take to fill your lab with aerosolized HF and shrapnel.

Even working at negative pressures, you can easily end up with a positive-pressure manifold if your sample is unexpectedly evolving gas at a higher than usual rate, or your valves aren't configured as intended. To be clear, these aren't academic exercises; I've actually seen all of these happen. With closed systems, you have to anticipate explosive pressures and plan accordingly. HF is incompatible with that kind of failure.

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