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I was browsing the internet looking for a neutron counter and came across an SNM-13 tube online. A little additional research reveled that its a boron trifluoride tube. A quick google search revealed that boron trifluoride has an LC50 of 1227ppm. That is not far behind hydrogen fluoride's 1276ppm. How much BF3 is in one of these tubes? If one was to leak, would it pose a significant health hazard? Obviously I'm not going to be huffing the stuff, but still.

Hi Ryan. Good thing to wonder about. Easy to get scientific in the Internet era, but beware of fake news.

The BF3 pressure in my proportional counter tube is a little below atmospheric. So if a small crack or hole appeared, the stuff would not spew out. Total pressure inside and out would rapidly equalize. Then BF3 would have to diffuse out while air diffused in. Might take minutes, hours, or days for half of the original fill to escape. Don't know about pressure in SNM-13 / CHM-13, but it's probably in the data sheet along with mechanical dimensions.

Suppose the gas all came out at once, for example if you cut the tube in half or crushed it flat, and became diluted in the room air.
What's the minimum volume of air in which BF3 concentration would become less than 25 ppm? That's the IDLH (immediately dangerous to life or health) level in USA safety regulations.

If that exercise is outside the scope of your physics knowledge, we'll be glad to help. I will wildly guess that if we compare workplace Permissible Exposure Levels, the toxicity represented by BF3 in one detector tube is less than that represented by mercury in one fluorescent lamp.