Hey everyone I was just informed about this
thread. I have done some reserch on this topic several months ago.
this is a copy paste of things I found.
--------------------
technical: Micron = µ = Micrometer = µm (different sources use these interchangeably)
To clarify
1. It is amorphous not cristalline.
2. The fibers we use are too large to inhale past the
throat.
3. If you got some in your mouth you would just spit it out or swallow it.
4. Silica fiber undergo dissolution and transverse breakage due to amorphous structure.
Source:
http://www.atsdr.cdc.gov/toxprofiles/tp161-c2.pdf
Different studies have used different rules for counting fibers in air samples, but in general, a fiber is a particle that has a length ≥5 µm and a length:diameter ratio (aspect ratio) of ≥3:1 or ≥5:1. The WHO counts fibers as particles with lengths >5 µm, widths <3 µm, and aspect ratios ≥3:1. The National Institute for Occupational Safety and Health (NIOSH) counts fibers as particles with lengths >5 µm and aspect ratios ≥3:1. The levels of synthetic vitreous fibers in air are measured by phase contrast microscopy (PCM), transmission electron microscopy (TEM), or scanning electron microscopy (SEM) (see Chapter 7 for more details). A human respirable fiber (a fiber that can be inhaled and reach the lower air-exchange portion of the respiratory tract) is usually defined as a fiber having a diameter <3 µm.
...key determinants of toxicity including:
The amount of material deposited in the alveolar region of the lung (fibers with diameters >3 µm do not reach this region; they are deposited in the upper respiratory tract and lung conductive airways, cleared by mucociliary action to the pharynx, swallowed, and eliminated via the feces);
The rate at which macrophages engulf and clear fibers deposited in the lower lung (human
macrophages cannot fully engulf fibers with lengths longer than about 1520 µm); and
The extent of movement of deposited fibers from the alveoli to the lung interstitium and the
pleural cavity (fibers with diameters >0.30.4 µm may move less freely into the interstitium and
pleural cavity).
Fibers that can dissolve in physiologic fluids (i.e., that are less durable) develop weak points that can facilitate (1) transverse breakage by physical forces into shorter fibers and (2) faster clearance by macrophages, compared with fibers that do not dissolve, like amphibole asbestos fibers.
Synthetic vitreous fibers differ from asbestos in two ways that may provide at least partial explanations for their lower toxicity. Because most synthetic vitreous fibers are not crystalline like asbestos, they do not split longitudinally to form thinner fibers. They also generally have markedly less biopersistence in biological tissues than asbestos fibers because they can undergo dissolution and transverse breakage
Note: I underlined the above.
I have never measured a silica fiber used in any
ecig product that was smaller diameter than 8 µm, most were between 20 and 35 µm.
-------------------
From: 02-23-2013
There are two types of silica, amorphous and crystalline. The silica fiber used in ecig wicks and electrical sleeving are amorphous, this form does not break down into the very small bits that cause silicosis. Even if they were deeply respirable, the amount (volume) of these fibers needed to cause enough mechanical damage to the lungs to be noticeable is basically impossible in ecig use. The natural airway defenses to particles larger than (aerodynamic diameter)(F*ds) ~4μm is very good and you would just cough it up or digest it.
In the first test I did the average diameter of a ecig wick fiber was ~8μm with a aerodynamic diameter of 16μm under fast inhalation velocity ~5m/sec.
edit: I miscalculated the aerodynamic diameter of the wet 8µm wick. The correct number is 24µm not 16µm.
Document Display | NSCEP | US EPA
Pathophysiology Treatment of Inhalation Injuries - Jacob Loke - Google Books
http://www.industrialventilation.ne...Impactor Data Reduction/Impactor_Park (1).pdf
What are the Effects of Dust on the Lungs? : OSH Answers
How Do Particulates Enter the Respiratory System? : OSH Answers
http://www.aeronautics.nasa.gov/pdf...ective_tile_care_and_handling_precautions.pdf
http://www.specialtygaskets.com/files/silicacloth-12.pdf
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1567293/pdf/envhper00401-0085.pdf
Next day edit: 02-24-2013
I just spent the afternoon looking at some samples of silica wicks donated from friends and vivi novas and a few venders. All were in the 20-32μm diameter range. Seems like the really small ones (~8μm) have gone out of fashion. I'll post some pics in a bit. (see pics in next post)
