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Author: Subject: Dilute Hydrofluoric Acid Safety

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[*] posted on 21-1-2022 at 11:55
Dilute Hydrofluoric Acid Safety

Unfortunately, I finally have the need for a dilute HF solution for inorganic/analytical chemistry. While I have worked with HF before in a research setting, it was always done under the fume hood, so I was never able to judge how much fumes were being emitted, and I think the perceived danger was much lower.

However, I do not own a fume hood currently :( While I can make it in situ e.g. F- and H2SO4, I would prefer higher purity and sulfate can't be present for my application.
As such, I have been thinking of getting a 0.5% standard HF solution. (The other possibility is 10%, but I think that is too high for me and I would definitely have to dilute it. Hopefully 0.5% is enough)

Is it feasible to work with a dilute HF solution (like 0.5%) outside a fume hood? Naturally, the other safety precautions (thick gloves, gas mask, spill kit, calcium gluconate) will still be in place. Would fuming be a significant issue (especially if heat is produced)?
I've also been told before that such low concentrations can be handled just like moderately concentrated H2SO4, but I've always liked to be on the safe side.

Is it safe to store it along with other acids?
As much as higher concentrations are OTC for some, I can't get my head around it. (Honestly, the way conc. HF was stored almost like any other acid in my research lab was quite funny - and also terrifying.)

And just out of curiosity, what concentrations do you feel safe using? :)
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[*] posted on 22-1-2022 at 22:15

I just read about someone who spilled a small amount 80% HF on their legs and died. 0.5% is less dangerous though.
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[*] posted on 22-1-2022 at 22:43

Considering the very very over the counter (grocery store) product Whink is a 3% solution and used to clean glass I would say it’s quite safe to use outside a hood.

Should add I’ve known people that smoke drugs like cannabis, methamphetamine, DMT etc that use Whink to clean glass pipe with zero safety precautions… get it all over their hands and seemed to suffer no real bad effects, assuming they washed it off quickly!

[Edited on 23-1-2022 by crow6283]
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[*] posted on 28-1-2022 at 16:08

Thanks! I've seen some other OTC cleaners with HF labelled under the ingredients (assuming its correct), and I never see any safety labels (unlike Whink which has some). Then again, I've never tried messing with any of them.

What concentration do you think would be the limit to using outside a hood then?
I probably will stick to the 0.5% though, thanks!

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[*] posted on 29-1-2022 at 03:11

I have experience with 48% HF, and acid at that concentration can be used fairly safely outside a fume hood. Solutions of HF fume MUCH less than solutions of HCl or HBr. This most likely is because of the much higher boiling point of HF (appr. 20 C), while HCl and HBr have boiling points of tens of degrees below 0 C.

I dilute 48% HF to 25% or so, and then there is no fuming at all anymore. At 48% there is some faint fuming. So, I would suggest you to buy the 10% solution. It will certainly be free of fumes. Storage of a 10% solution is more practical than storage of a 0.5% solution. You will need a lot of volume in the latter case.

Skin-contact is another story. Avoid contact with skin at any cost, also with solutions of 10% or even less. The 3% OTC product I certainly would not want to have in contact with my skin. I do not know of such an OTC product where I live, and I hope that the bottle of that product has clear warnings about the risk of skin-contact with the liquid.

[Edited on 29-1-22 by woelen]

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[*] posted on 31-1-2022 at 16:15

I've worked with 48% HF before as well, but I've never used it outside the fume hood. Thanks woelen for the insight!

I'll make sure to avoid skin contact.
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[*] posted on 31-1-2022 at 17:26

First up, I have no experience working with HF. The below is by no means exhaustive, but hopefully gives you an idea of what you are working with below 10%, between 10 - 40% and above 40%.
I have read a few of the Australian industry standard practices for working with HF, which are presumably similar globally.
The main relevant points are:
- Only purchase/store HF at the maximum concentration required for your needs.
- Use automated dispensing when possible
- All work with 40% plus concentration must be done under a hood
- Always add the acid to water for dilution if required
- Never work alone with concentrations greater than 10%
- ensure calcium gluconate gel (antidote) is available, stored below 25°C and within the expiry date
- store HF bunded at or near ground level, well ventilate, away from direct sunlight and away from non compatible chemicals.

PPE beyond standard laboratory PPE
- Face shield, nitrile gloves, PVC apron and respirator with acid gas cartridges for 40% plus.
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