Respiratory filters

Fig. 6.38 Selection of various power-assisted respiratory filtering devices, (a) Respiratory hood (b) light respiratory hood (c) respiratory helmet ...

Fig. 6.47 Respiratory filter for escape with a mouthpiece assembly, partly unpacked (left) and in practical use (right).

Because a filter sample includes particles both larger and smaller than those retained in the human respiratory system (see Chapter 7, Section III), other types of samplers are used which allow measurement of the size ranges of particles retained in the respiratory system. Some of these are called dichotomous samplers because they allow separate measurement of the respirable and nonrespirable fractions of the total. Size-selective samplers rely on impactors, miniature cyclones, and other means. The United States has selected the size fraction below an aerodynamic diameter of 10 /xm (PMiq) for compliance with the air quality standard for airborne particulate matter. 

Compressed airline system a faeepieee or hood is eonneeted to a filter box and hand-operated regulator valve whieh is provided with a safety deviee to prevent aeeidental eomplete elosure. Full respiratory, eye and faeial proteetion is provided by full-faeepieee versions. The eompressed air is supplied from a eompressor through a manifold or from eylinders. 

SX gas filters and combined filters against specific named compounds used m respiratory... 

Respiratory protective devices - Powered filtering devices incorporating a helmet or a hood - Requirements, testing, marking. Superseded BS EN 146 1992... 

Diatomaceous earth, widely-known and long-used as a filteraid in process and waste filtrations, has a high microcrystalline silica content. As well as being a respiratory hazard in the workplace, the silica is being scrutinized in some jurisdictions as a potentially hazardous dust in landfills in which spent filter cakes are deposited. 

A written respiratory protection program is required when necessary to protect the health of the employee from workplace contaminants or when the employer requires the use of respirators. A limited written program is also required when respirators (other than dust masks) are being voluntarily worn by employees. This latest document states It is the intent of the standard that the employer would not be required to incur any costs associated with voluntary use of filtering facepieces other... 

Particles are present in outdoor air and are also generated indoors from a large number of sources including tobacco smoking and other combustion processes. Particle size, generally expressed in microns (10-6 m) is important because it influences the location where particles deposit in the respiratory system (U.S. Environmental Protection Agency 1995), the efficiency of particle removal by air filters, and the rate of particle removal from indoor air by deposition on surfaces. 

Studies on the particulate distributions from compressed natural gas (CNG) or diesel-fuelled engines with diesel oxidation catalyst (DOC) or partial diesel particle filter (pDPF) have also been performed. The results obtained are used as data for the model, to study the particle penetration into the human respiratory tracts. As a result, the number distribution of particles in different parts of lungs can be modeled [99-101]. Understanding the particle formation and their effects and finding the methods to ehminate the formed particulates from exhaust gas contribute to a cleaner urban environment and thus to a better quality of life. 

The collection of air samples using air tubes and/or filters is of value during the course of the field research when performing SDDBM studies. The air tube/air filter data can be used to estimate the portion of the total body burden, which originates from respiratory exposure to the active ingredient. Of course, if an organic vapor respirator is used by the worker as a matter of course, the respiratory exposure component should be backed out of the final exposure calculation. 

Respiratory Chromosorb air tubes and Gelman filters, air pump... 

It has been demonstrated that it is possible to lower the level of airborne radon progeny by filtering and/or expose the air to an electric field. If the radiological risk is measured by the potential alpha energy concentration (PAEC) or exposure rate, for instance expressed in J m 3 or WL, the level may be lowered to about 10-20 % of the value in untreated air, while the reduced level may only be about 40-50 % of the untreated one if the average dose to a certain part of the respiratory tract, for instance expressed in Gy year 1, is considered. 

High-efficiency particulate air filters can remove lightweight particles such as pollens, mold spores, and cat allergen, thereby reducing allergic respiratory symptoms. 

Dusts and other insoluble materials present a particular difficulty to the lungs. Particles that enter the alveoli are removed slowly. For dusts the following simple rule usually applies The smaller the dust particles, the farther they penetrate into the respiratory system. Particles greater than 5 /xm in diameter are usually filtered by the upper respiratory system. Particles with diameters between 2 and 5 /xm generally reach the bronchial system. Particles less than 1 /xm in diameter can reach the alveoli. 

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