Respirable fibers

Fibers are of special concern, and are defined by WHO as having the dimensions 

In particular, thin fibers with a diameter below 1 pm can reach the alveoli and show a health-endangering potential. 

The deposition behavior of particles in the different regions of the respiratory tract is shown in Fig. 2.14. 

A high proportion of the occupational diseases caused by special substances are diseases of the respiratory tract, in particular, so-caUed pneiunoconiosis in the mining industry and silicosis, which is activated by quartz and particulate matter. Although these dusts themselves are not toxic, they can lead to chronic pulmonary damage as a result of an overload of the cleaning systems of the respiratory tract 

Biopersistant particles in the alveoH can only be removed by an active transportation process performed by the macrophages. If the cleaning system has transported the particles to the ciha, further ehmination is performed by the cilia as described above. The half-Hfe period for ehminating biopersistent particles 

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Glass fibers <3 fim are to be avoided because these are classed as respirable fibers which can enter and damage lung passages. Most glass fiber products have sufficient fiber lengths to prevent lung entry even if their diameters are <3 fim. 

When using animal inhalation studies for assessment of the risk to human health of airborne fibers, it is critical to demonstrate that the characteristics and concentrations of the experimental fiber aerosols are comparable to those in human exposure situations." NIOSH has two criteria for defining fibers A rules (total fibers) and B rules (respirable fibers)."... 

Toxicology. The toxicity of calcium silicate depends on particle size, aspect ratio, and amount of silica and respirable fiber. Synthetic nonfibrous calcium silicate is considered to be a nuisance dust. 

Respirable fibers may be quite long and extend beyond 50 pm. However, the most important factor in the deposition of fibers, such as asbestos, is the diameter of the fiber, not the length. Fibers of small diameter (0.5 pm) will remain suspended in the airway and drift with the airflow to be deposited in the airspace. 

Potassium titanate whiskers were found to improve the tribological properties of NAO friction materials. These soft, synthetic refractory materials stabilize friction level, reduce pad wear, noise, fade, thermal conductivity, control porosity, and provide thermal reinforcement. Fibrous potassium titanates are being replaced by platelet and powder versions because of health concerns associated with respirable fibers. 

Several methods exist for the determination of respirable fibers. In the case of asbestos fibers, unspecific light microscopic techniques [6-110] as well as highly sensitive X-ray methods can be employed [6-111]. Differentiation from inert fibers, e.g., fibers of gypsum, is only possible with the latter method, although light microscopic analyses are more cost effective. All these procedures are suitable for the determination of total respirable fibers, especially for determining the concentration of man-made mineral fibers. 

D. B. Warheit, K. L. Reed, K. E. Pinkerton, and T. R. Webb. Biodegradability of inhaled p-aramid respirable fiber-shaped particulates (RFP) Mechanisms of RFP shortening and evidence of reversibility of pulmonary lesions. Toxicol. Lett., 127(l-3) 259-267, Febmary 2002. 

Inhalation is the most important route of exposure to fibers. Only some fibers can be inhaled and deposited in the respiratory tract. The respirability of fibers is largely determined by two variables density and cross-sectional area length plays only a minor role in determining respirability. Fibers with aerodynamic equivalent diameters between 5 and 10 pm can deposit in the larger airways, and those less than 5 pm can reach the terminal bronchioles and alveoli. This latter aerodynamie diameter is equivalent to a fiber diameter of approximately 3 pm however, density will also affect this value. 

Ethers, esters, amides and imidazolidines containing an epithio group are said to be effective in enhancing the antiwear and extreme pressure peiformance of lubricants. Other uses of thiiranes are as follows fuel gas odorant (2-methylthiirane), improvement of antistatic and wetting properties of fibers and films [poly(ethyleneglycol) ethers of 2-hydroxymethyl thiirane], inhibition of alkene metathesis (2-methylthiirane), stabilizers for poly(thiirane) (halogen adducts of thiiranes), enhancement of respiration of tobacco leaves (thiirane), tobacco additives to reduce nicotine and to reduce phenol levels in smoke [2-(methoxymethyl)thiirane], stabilizers for trichloroethylene and 1,1,1-trichloroethane (2-methylthiirane, 2-hydroxymethylthiirane) and stabilizers for organic compounds (0,0-dialkyldithiophosphate esters of 2-mercaptomethylthiirane). The product of the reaction of aniline with thiirane is reported to be useful in the flotation of zinc sulfide. 

This Chapter provides information on available certified reference and quahty control materials relevant for use in the measurement of airborne contaminants in occupational hygiene. The majority of measurements made in this area worldwide are solvents, dust (total, respirable), elements, oil mist, quartz, fiber identification (asbestos, man-made fibers), mists and gases. 

McGowan SE. 2007. Vitamin A deficiency increases airway resistance following C-fiber stimulation. Respir Physiol Neurobiol 157 281-289. 

The 2003 ACGIH threshold limit valuetime-weighted average (TLV-TWA) for graphite (except graphite fiber) is 2mg/m as respirable dust. 

These results have suggested that mineral dusts that are inert in a particulate form may have biological activity when they occur in a fibrous form. Factors affecting fiber toxicity include length, diameter, respirability resistance to chemical dissolution in biological fluids, and durability. "... 

Smart fibers can make smart sutures—threads used by surgeons to sew up incisions—such as suture that ties itself when heated And Sensatex Incorporated makes a smart shirt that automatically monitors the wearer s vital signs. Special sensors and conducting fibers embedded in the shirt measure heart rate, respiration, and body temperature, and a tiny controller relays this information by transmitter to a medical station. 

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