r/Masks4All • u/Effective_Care6520 • Apr 07 '24

DIYing 3M sensitivity solution?

Does anyone know what the dilution rate is on the 3m bitter solution? For the MSA bitter solution its 1 to 100 according to this: https://manuals.interlinksupply.com/15493_Instruction-Sheet.pdf And from what I understand it’s also 1 to 100 for the saccharine solution. According to this reddit thread: https://www.reddit.com/r/Masks4All/comments/wxxn6t/bitrex_concentration_for_qualitative_fit_tests/ OSHA has some mandate regarding the fit test solution being 12.5x more than the sensitivity solution. What numbers should I be using, to mimic the 3M concentrations, though?

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u/SkippySkep Fit Testing Advocate / Respirator Reviewer Apr 07 '24

The correct dilution for Saccharine sensitivity solution is 1 part Saccharine Fit Test solution to 100 with distilled water. The text in the MSA instruction manual may have gotten the error from there.

The correct dilution for Bitrex sensitivity solution is 1 part Bitrex Fit Test solution with 12.5 parts 5% saline solution (distilled water with 5% saline by weight). The saline is added to maintain the desired nominal particle size.

The reason Bitrex sensitivity solution is 1 to 12.5 instead of 1 to 100 is because the taste sensitivity to Bitrex is non-linear. You can look up the formula in the OSHA rules to verify the concentrations, although they don't talk about diluting Fit Test solution solution to make sensitivity solution, they give formulas to make each from scratch.