> Inhalable are those that do damage anywhere
> from the tip of the nose to the deep lung. Thoracic do damage from the
> brachial tubes and deeper. Respirable do damage only when down deep in
> the gas exchange region of the lungs.
Right, but the distinction between those categories is size. Respirable
particles are less than 0.2 microns in size.
> You are mistaken with regards to silicosis and the belief that every
> particle stays and does damage. This is what the respirable fraction
> ratio to size is about.
No, the respirable fraction ratio is about percentage of the sample falls in
the respirable size range. It's a symptom of inadequate collection and
processing methods, that the sample contains particles not in the size range
of interest.
> Large particles cannot enter the deep tissues
> in the first place due to physical size.
Right. That's why they're not respirable particles.
> As the particles get smaller,
> they are more likely to be able to enter the deep tissues of the lung.
Precisely. Although below some minimum size, they probably no longer do as
much harm.
> Further, of
> those particles that do enter deep lung tissue, not all are retained.
> Many are exhaled.
I would be very surprised to see any experimental data that shows once a
respirable particle is in the tissue (as opposed to still suspended in air
inside the lungs or trapped in mucus higher in the lungs), it is likely to
be exhaled. References please.
> Please do see Appendix C: Particle Size-Selection Sampling Criteria for
> Airborne Particulate Matter, of the current 2004 ACGIH TLV and BEI's
> handbook. It's pages 73-76.
Don't happen to have a copy of that on my bookshelf ... but PM2.5 addresses
only particle size, not the composition or shape of the particle. And
PM2.5, basically all particles smaller than 2.5 microns, covers a lot of
particles that are not respirable (larger than 0.2 microns), and hence not
likely to cause silicosis.
> Dirt roads are one of the primary sources of PM2.5 or PMfine as it
> often called.
That's true, but those particles are not primarily respirable sharp silica
particles like those that cause silicosis. Diesel smoke also has a lot of
PMfine, but it doesn't cause silicosis either. Other lung diseases perhaps,
but not silicosis.
> Beaches depend on the type of sand, type of water, etc.
> A calm coarse sand will have less PMfine then a heavily trafficked fine
> sand beach will have. This has been well documented by the US EPA, and
> others, who have performed studies on the subject.
Do you have a report that shows what percentage of the PMfine collected from
the air over beaches is respirable silica ? Beach sand is kind of like the
water in the ocean, how dangerous it is depends on what you do with it. I
wouldn't care to breathe either one, but neither one is likely to give you
silicosis.
See, the problem is that the EPA and it's subsidiaries have never been
strong on science. In this case, they've said "We know this thing is bad,
but we can't test for it directly, so we will test for this other thing that
might contain the bad thing". Ok, that's fine, but it does not make the
thing that they test for synonymous with the bad thing. Running around
counting haystacks does not tell you how many needles you have.
Randall
|