Bill, like Kate I simply don't understand why you would want to do this.

I am curious, partly as you have posted two closely related threads this month!

Do you just want to theorise when there is a long standing internationally agreed methodology for evaluating the level of risk?

Bill

That does clarify and I will add another consideration to the original questions you have asked!

When Man Made Mineral Fibres aka Triple M Fs first came on the scene the fibre sizes were (relatively speaking) huge, but the manufacturers were trying to position MMMFs as substitutes for the A word, so they made the fibres progressively smaller until they mimicked crocidolite or amosite fibres when seen under the microscope.

...and so the very first exposure standards were set BEFORE the bad news that could be anticipated perhaps a decade or more after exposure - application of the so called "precautionary principle".

But, of course those standards use exactly the same terminology as in place for asbestos fibres.

I think you would be very, very lucky to get any user of these Forums to hazard a guess as to how to convert fibres per ml into some other unit, other than by gravimetric analysis but using that you would be counting not just asbestos and the other fibres you mention but all the other contaminants.

One for an industrial hygieniest (not many of them in the UK) or a heating and ventilation engineer.

Possibly British Occupational Hygiene Society (BOHS) or CIBSE might either have guidance or some networking group.

Alternatively (and I am thinking that there are SOOOO many more industrial hygienists in the USA) you could see whether there is anything from the American Society of Safety Professionals (ASSP, previously ASSE when the last word was Engineers).

.....or go on LinkedIn where there is an Asbestos Discussion Group and knowledgeable contributors.

Good luck, Peter

Bill,

Complicated stuff, hence the difficulty in assessing airborne asbestos created in contaminated soils work, see Asbestos in Soil (claire.co.uk).

Would it help to know that TDN13 in 1970 equated 2f/ml to 0.1 mg/m3? That being the effective control limit at the time.

See https://nyaspubs.onlinelibrary.wiley.com/doi/abs/10.1111/j.1749-6632.1965.tb41108.x and Asbestos Dust and its Measurements. (cabdirect.org) via googlescholar.

Research was ongoing in the 60's to develop controls and eventually settled on the current counting method (fibre rather than gravimetric) in the 70's. Long and short is: there is no reliable comparison (so far as I am aware). The Asbestos Removal industry uses H14 HEPA filtration 99.997% as opposed to H13, 99.97%, arguably on a "best available technology, not involving excessive cost" basis, although there is no HEPA 15 standard.

That can be a rabbit hole too, see "Submicron and Nanoparticulate Matter Removal by HEPA-Rated Media Filters and Packed Beds of Granular Materials" for an understanding of how HEPAs are thought to work at particle sizes below PM2.5.