Rank: Forum user 
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HI All.
I am a newbie and and I am not a Hygienist, but have occasionally delved into environmental engineering relating to asbestos analysis.
Hoping to get some assistance with a issue that I have often seen in publications- my question is probably suited for an experienced hygienst but i welcome all contributions.
I have seen in past reports/journals (and studies) that a small cut into asbestos fibre cement sheeting with an angle grinder (for example) can liberate approx (5fb/ml to 20fb/ml). Similar with drilling a 10mm hole (3fb/ml). These are rough estimates based on PCM analysis and it does vary of course...but the quantum of fb/ml is about right.
BUT... I have also seen some publications stating that only "1mg of asbestos" is sufficient to generate 33PCM fb/ml per 1 m3. (Apparently this is a rough conversion used by hygienists). This conversion of 1mg to fb/ml is referenced in some past studies undertaken in the 1980's £ believe.
Cutting or drilling into an asbestos sheeting will disturb far more (ie much much more!! ) than 1mg of asbestos...even if one were to assume only 20% of the cement sheeting contained asbestos. Obviouly, using an angle grinder, for example, will gut many many grams of asbestos cement!!!
So my question : How can 1mg be stated as releasing 33PCM fb/ml yet cutting or drilling only liberate 5 to 20fb/ml - noting the latter disturbs orders of magnitude of more material.
Many thanks for any help
Bill
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Rank: Super forum user 
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I'm not quite clear about the units here - I see 33 fb / ml as representing a concentraton of fibres in air (number of fibres divided by the volume of air they are contaminating) , but what what does 33 fb / ml per 1 m3 mean - per cubic metre of what?
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Rank: Super forum user
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Looking again at the title rather than the content of your post, is the claim you are scrutinising actually that "a concentration of 1 mg of asbestos per cubic metre of air is equivalent to a count of 33 fibres of asbestos in 1 millilitre of air"?
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Rank: Forum user
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Dear Kate. Yes you are absolutly correct. I am scrutinising how 1mg of asbestos in 1m3 of air can possible equate to 33fb/ml pcm.
its actually also published in the TOXICOLOGICAL PROFILE FOR ASBESTOS which is freely available online.
Apologies for not being clearer with my units. But i would like to get to the bottom of how 1mg/m3 is equating to 33fb/ml when clearly on site measurements are vastly lower(for much larger quatities of disturbed asbestos material)
hope that makes sense.
regards
bill
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Rank: Super forum user
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OK that makes sense. The way you would get from 1 mg of asbestos in 1 m3 of air to 33 (or however many) fibres of asbestos in 1 ml of air is by knowing first, how much does a fibre of asbestos typically weigh. Then, you can say how many fibres are in 1 mg of asbestos.
So then you can say for each mg of asbestos in 1m3 of air how many fibres are in 1m3 of air. Next you work out how many millilitres are in a cubic metre (lots), and you use that to convert the fibres in 1m3 to the fibres in 1ml. It's just an arithmetic conversion between units that measure the same thing, as if you were converting from miles to kilometres. In the same way as how long you expect a journey to be has no bearing on the conversion factor you use to convert between miles and kilometres, the concentration of asbestos that you expect to find has no bearing on the conversion factor you use to convert between mg/m3 and fb/ml. Edited by user 24 October 2021 09:00:38(UTC)
| Reason: inadvertent invention of a new cgs unit
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Rank: Forum user
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hi Kate. My issue is not the calculation. thank you for replying i appreciate it.
It is in the origin of of 33fb/ml from 1mg of asbestos whixh i have an issue with.
It makes no sense since personal samplers record less "fb/ml" after contractors ( in the real world application) cut and saw "tens of grams" or even "kilograms" of asbestos cement material.
So only 2 things can be happening. Either the sampler is underestimating the onsite count OR the 33fb/ml is ridiculousoly high for 1mg.
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Rank: Super forum user
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It's the origin I was trying to describe above - I'll try again, putting it differently. The two measures (mg/m3 and fb/ml) are both measuring how contaminated a sample of air is with asbestos, just in different units . Suppose there is 1 mg of asbestos in 1 m3 of air. (It doesn't matter for now how it got there.) Then you work out from the typical weight of asbestos fibres how many fibres that is in your 1m3 of air. Then you work out how many fibres that would be if you only had 1 ml of the same contaminated air. This is what would give the result of 33 (or whatever the correct factor is.) It's not about what would happen if you disturbed 1 mg of asbestos.
It's about how if you had 1 mg of asbestos in a 1 m3 air sample, how many fibres of asbestos you would find if you took just 1 millilitre of that 1 m3 air sample instead of all of it, and measured the asbestos by counting the fibres instead of by weighing it. So in the first case, you weigh how much asbestos is in your big air sample. In the second, more practically, you count how many fibres of asbestos are in the small air sample.
Then the calculation that you use the 33 for is to scale between however many mg of asbestos per cubic metre there actually are in your particular sample, and how many fibres per millilitre there are.
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hi kate.
oh i see.
i know historically hygienists have used the 33fb /ml to determine approx airborne concenteatios based on a known mg/m3 value.
i was always sceptical of it. ie some reseachers have been provided with a "measured" mg /m3 of asbestos .. say in a factory somewhere...
and say that it was 2mg/m3 measured in 1976 in a chrysotile factory....then they back calculate that the approx fb/ml must have been around 66fb/ml.
this bithers me .
thanks again for explaining your view .. i appreciate it
bill
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Rank: Super forum user
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Morning Bill There is also the problem that I don't think you are not comparing like for like, but an occupational hygienist would be better capable of explaining the science. The gravimetric assessment in mg per m3 will count total dust generated not only the asbestos content UNLESS somebody was using a method that separated the asbestos from other conraminants, in your case cement dust.. Various attempts have been made to come up with reliable conversion factors between mg/m3 and fibres per ml. Results rather inconsistent partly as the asbestos content in the dust will vary according to percentage content, level of friability and what is being done such as wet/dry Lots of discussion in this paper I found with a Google search https://hrcak.srce.hr › file PDF by M Dodič-Fikfak · 2007 — per millilitre (f mL-1) = 0.1 mg m-3 asbestos dust. “may be used” to make gravimetric measurements comparable to fibre number concentrations in f mL-1
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Out of interest, what do you think is wrong with the 66 fb/ml figure in that example - is there a reason you see this as unrealistic?
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Rank: Super forum user 
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As the natural crystalline fibres are quite long how does cutting and drilling ever release whole individual fibres? Given any release is always fragments why do they bother with the fibres/ml measurement?
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Rank: Super forum user
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As the natural crystalline fibres are quite long how does cutting and drilling ever release whole individual fibres? Given any release is always fragments why do they bother with the fibres/ml measurement?
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Rank: Super forum user
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Roundtuit, the long natural asbestos fibres will get broken in the process of making the cement for sure, and cutting will certainly make them into dust, for respiratory hazard the danger length is around 3.5 microns especially those that may have that little hook you see in the natural state (under a microscope)
So the question I have is does the fibre count include just the danger length/range ? Edited by user 24 October 2021 14:41:23(UTC)
| Reason: Added question
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Originally Posted by: Roundtuit  As the natural crystalline fibres are quite long how does cutting and drilling ever release whole individual fibres? Given any release is always fragments why do they bother with the fibres/ml measurement?
Hi - the reason is that the "fragments" which are airborne are just as important (and realisticlly more important as they are more likely to be a respirable size).
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Originally Posted by: Kate Out of interest, what do you think is wrong with the 66 fb/ml figure in that example - is there a reason you see this as unrealistic?
Hi Kate
The problem is I have no scientific reason to say it is not correct. All I have is data from on site works where far less fb/ml occurs by disturbing much more material. i will upload a paper in as part of this discussion to highlight what i mean.
Peter just attached a paper (Thank you again Peter) and in that paper you will see conversion factors are much lower than 33!
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Originally Posted by: JohnW Roundtuit, the long natural asbestos fibres will get broken in the process of making the cement for sure, and cutting will certainly make them into dust, for respiratory hazard the danger length is around 3.5 microns especially those that may have that little hook you see in the natural state (under a microscope)
So the question I have is does the fibre count include just the danger length/range ?
John - That is a legitamate comment. But the document i have does in fact say the 1mg/m3 = 33fb/ml is PCM fibres.
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Rank: Super forum user
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Originally Posted by: bill4000 Hi - the reason is that the "fragments" which are airborne are just as important (and realisticlly more important as they are more likely to be a respirable size).
Not really an answer as to why we persist with fibres/ml - "fragements" will be captured in the mg/m3 value.
How many fragments = one fibre?
You seem to concur a full length fibre in itslef is not a "respirable size".
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Rank: Super forum user
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Originally Posted by: bill4000 Hi - the reason is that the "fragments" which are airborne are just as important (and realisticlly more important as they are more likely to be a respirable size).
Not really an answer as to why we persist with fibres/ml - "fragements" will be captured in the mg/m3 value.
How many fragments = one fibre?
You seem to concur a full length fibre in itslef is not a "respirable size".
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Rank: Forum user
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This is another link (below)...page 13 discusses the conversion factors. In this paper, the mg/m3 of dust is based on pure asbestos dust.
The paper also references the factor of "30" but concedes it is unexplainable. In fact it suggests higher factors depending on the type of asbestos.
https://www.google.com/u...aw3MUbPYh9daCARRlQxwe-2e
The Curious thing ... which i guess underscores my issue is that the 2 papers I linked demonstrate high conversion factors from mg/m3 to fb/ml. Yet real world data from personal samplers ( and the paper referenced in Peter's reply) show much much lower conversion values.
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Originally Posted by: Roundtuit <p><div class="quote"><span class="quotetitle">Originally Posted by: bill4000 <a href="/posts/m811830-Abestos-mg-m3-to-fb-ml-discrepancy#post811830"><img src="/Themes/iosh2/icon_latest_reply.gif" title="Go to Quoted Post" alt="Go to Quoted Post" /></a></span><div class="innerquote">Hi - the reason is that the "fragments" which are airborne are just as important (and realisticlly more important as they are more likely to be a respirable size).</div></div>
</p><p>Not really an answer as to why we persist with fibres/ml - "fragements" will be captured in the mg/m3 value.
</p><p>How many fragments = one fibre?
</p><p>You seem to concur a full length fibre in itslef is not a "respirable size".</p>
hi roundtuit.
maybe i missed something here. but i am not looking at the diff between fragment or full fibres.
the issue is respirable fibre of wich pcm would measure (and the conversion from mg/m3 to f/ml)
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Rank: Super forum user
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I don't understand how you arrive at the conclusion that real world samplers show different conversion values. To do that, you would need to take a sample of contaminated air and measure its degree of contamination by asbestos in two different ways: 1. Weigh the quantity of asbestos in the air sample and scale the weight of it to 1 m3 of air. 2. Count the number of asbestos fibres in the sample and scale the count of fibres to 1 ml of air. The ratio between these two results is the conversion factor (whether it be 33 or something else). It doesn't seem likely that this is what is happening in your sampling but maybe it is?
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If science is so pure and absolute why are there so many constants to make the subsequent mathematics work? Your reference document pretty much sums it up: For the purposes of making rough calculations when a more accurate conversion factor is not available, it has been assumed that a concentration of 1 mg/m3 in air is equal to 33 PCM f/mL (EPA 1986a). The source of your consternation is therefore EPA 1986a.
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Rank: Super forum user
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If science is so pure and absolute why are there so many constants to make the subsequent mathematics work? Your reference document pretty much sums it up: For the purposes of making rough calculations when a more accurate conversion factor is not available, it has been assumed that a concentration of 1 mg/m3 in air is equal to 33 PCM f/mL (EPA 1986a). The source of your consternation is therefore EPA 1986a.
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Hi Bill...as an industrial hygienist working in the field for a wee while now and yes it is difficult to give you a straight answer to your questions - working internationally there are around 10 different Short term and long term exposure values to choose from - starting at 0.003 fiber/ cm3 .....when it comes to the caculation I personnaly always err on the conservative site so calcs will different but that should be explianed in the report as I would always make reference to level of 10% or 50% of the OELor against the statistical prediction for the 95%ile and hence why I think you may be seeing a discrepancy here...probably a combination of two things - a plethora of research data and opinion to choose from and the old human factor element or fear of being sued... :)
Sometimes you will come across a client that will want a better exposure limit value but that doesn't always happen as it takes money to achieve it...
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Originally Posted by: Roundtuit If science is so pure and absolute why are there so many constants to make the subsequent mathematics work?Your reference document pretty much sums it up:For thepurposes of making rough calculations when a more accurate conversion factor is not available, it hasbeen assumed that a concentration of 1 mg/m3in air is equal to 33 PCM f/mL (EPA 1986a).The source of your consternation is therefore EPA 1986a.
Agree it is rough...but my point was that the reult using 33pcm fb/ml is orders if magnitude higher than real worl abatement studies when asbestos is removed.
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Originally Posted by: stevedm Hi Bill...as an industrial hygienist working in the field for a wee while now and yes it is difficult to give you a straight answer to your questions - working internationally there are around 10 different Short term and long term exposure values to choose from - starting at 0.003 fiber/ cm3 .....when it comes to the caculation I personnaly always err on theconservative site so calcs will different but that should be explianed in the report as I would always make reference to level of 10% or 50% of the OELor against the statistical prediction for the 95%ile and hence why I think youmay be seeing a discrepancy here...probablya combination of two things - a plethora of research data and opinion to choose from and the old human factor element or fear of being sued... :)
Sometimes you will come across a client that will want a better exposure limit value but that doesn't always happen as it takes money to achieve it...
Good point Steve...i do still find it strange that a conversion factor can be so far out though. even if including a 50% saftey factor. The difference is orders of magnitude different.
To be honest i have seen research say 1mg/m3 can give rise to 1fb/ml and other say it can be all the way to 195fb/ml. The 33 value is justbone that is well published.
I am coming to the conclusion that the issue is indeterminable. and realistically a back calculation from mg/m3 should not apply to fb/ml.
it appears to be misleading
if anything, real world personal samplers of past abatement studies are more accurrate for determining retrospective studies .
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Rank: Super forum user
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BOHS just on this subject alone has over 100 pieces of refereced research for this topic and opinions....when counting fibers there is also a difference between labs and equipment used with varriations ranging up to 50% in the count...good debate but I'm not sure you will get a full answer to your question....
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Originally Posted by: stevedm BOHS just on this subject alone has over 100 pieces of refereced research for this topic and opinions....when counting fibers there is also a difference between labs and equipment used with varriations ranging up to 50% in the count...good debate but I'm not sure you will get a full answer to your question....
Lol. I dare say you are correct. Again thanks to all for your inputs
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