I'll be doing some work (as a software engineer) with a vacuum process chamber that consumes various nasty gases. There are numerous safeguards in the system, but as a cautious type, I decided to read the MSDS of the chemicals involved. The one that makes me the most nervous is tungsten hexafluoride; one mole apparently reacts with water to form 6 moles of HF, which I distantly remember from chemistry class as being bad news. Being largely composed of water, I find this troubling. If there were failures in the multiple safeguards and a leak did somehow occur, how could it be detected?
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3$\begingroup$ First off, +1 for reading the MSDS then being concerned about the potential formation of HF...really, nice going there. It looks like you've found a very serious concern, as your memories of the nastiness of HF are all too true. Personally, I think this is such a serious issue that it is a question for a safety engineer or some such person who is thoroughly familiar with your system. You can maybe get ideas to pass on from here, but you absolutely don't want to take an answer from here as a solution to your very specific, very serious issue. Regardless, good luck! $\endgroup$– airhuffFeb 19, 2017 at 20:01
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$\begingroup$ @airhuff, I'm sure the engineers in charge of safety are taking the proper safeguards, but I was posing this more as a question of how I could notice if something was wrong. I.e. what would be the warning signs of a leak? You're right that I should probably just ask the engineers, though, as they likely have plans in place for detecting and responding to serious accidents. $\endgroup$– Dan BryantFeb 20, 2017 at 0:24
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$\begingroup$ Yea, I didn't mean to discourage the question, it's just that chemists eyes pop out when they see "leak" and "HF" in the same paragraph ;) What is the chamber made of? $\endgroup$– airhuffFeb 20, 2017 at 0:35
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$\begingroup$ @airhuff, I don't know the precise details, but it's a heavy duty vacuum chamber and it's being built by folks who have experience working with these kinds of things. There are several layers of safeguards (all valves are inside a sealed box), so obviously the process guys take this stuff seriously; maybe I'm just overly paranoid. I was thinking more: if you're working with HCN and smell almonds, you know you have a problem; not sure what you can detect if you're exposed to HF. $\endgroup$– Dan BryantFeb 20, 2017 at 1:32
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1$\begingroup$ Your nose is very sensitive to F and Cl (and HF and HCl), at the parts per billion level. The threshold vales for harming you are higher. But, you smelling the intensely sharp acrid odor of a halogen (or halogen acid) is not, of course, calibrated. Usually continuous air monitoring is used, along with appropriate respirator protection when opening up the system. $\endgroup$– Jon CusterFeb 20, 2017 at 1:54
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1 Answer
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$\ce{WF6}$ is not an uncommon gas used in industrial manufacturing of semi-conductors. Commercial gas detectors are readily available, and will detect $\ce{WF6}$ down to low ppm range, which is about an order of magnitude less than the $\mathrm{LC}_{50}$ for rats, apparently.
You could google tungsten hexafluoride detector, but some examples include (no affiliation or endorsement):
- http://www.newcosmos-europe.com/gas-by-name/144-tungsten-hexafluoride-detection.html
- http://www.toxicgasdetection.co.uk/gas/?gas=Tungsten%20hexafluoride&search=Tungsten%20hexafluoride&form=gas&id=416
- https://www.gas-find.com/hexafluorure-de-tungstene.html
The most common type of detector is a diffusion monitor with electrochemical sensor. Some sensors actually use conversion of $\ce{WF6}$ to $\ce{HF}$, and then detect the $\ce{HF}$. Commercial $\ce{HF}$ detectors at low ppm range are also common.
