BS EN 481:1993 download free.Workplace atmospheres Size fraction definitions for measurement of airborne particles.
o Introduction
The proportion of total particulate matter which is inhaled into a human body depends on properties of the particles, on the speed and direction of air
movement near the body, on breathing rate, and whether breathing is through nose or mouth.
Inhaled particles can then deposit somewhere in the respiratory tract, or can be exhaled. The site of
deposition, or probability of exhalation, depends on properties of the particle, respiratory tract, breathing pattern, and other factors.
Liquid particles or soluble components of solid
particles can be absorbed by the tissues wherever they deposit. Particles can cause damage close to the deposition site if they are corrosive, radioactive, or capable of initiating some other type of damage.
Insoluble particles can be transported to another
part of the respiratory tract or body, where they can he absorbed or cause a biological effect.
There is a wide variation from one person to another in the probability of particle inhalation, deposition, reaction to deposition, and clearance. Nevertheless, it is possible to define conventions for size selective sampling of airborne particles when the purpose of sampling is health-related. These conventions are relationships between aerodynamic diameter and the fractions to be collected or measured, which
approximate to the fractions penetrating to regions of the respiratory tract under average conditions.
Measurement conducted according to these
conventions will probably yield a better relationship between measured concentration and risk of
disease.
NOTE Far fuflhr information on Ow factors uffvvting
inhalation and depoit.ion, and their application in itandards,
18). 191. 1101’ lii). (121 and 1131.
1 Scope
BS EN 481 defines sampling conventions for f particle size fractions which are to be used in
assessing the possible health effects resulting from inhalation of airborne particles in the workplace. They are derived from experimental data for
healthy adults. Conventions are defined for the inhal able, thoracic and respirable fractions; extrathoracic and tracheobronchial conventions may be calculated from the defined conventions. (The inhalable fraction is sometimes called inspirable — the terms are equivalent. The nomenclature of the fractions is discussed in Annex A.) Assumptions are given in clause 4. The convention chosen will depend on the region of effect of the component of interest in the airborne particles (see clause 3). Conventions are stated in terms of mass fractions, hut they may also be used when the intention is to evaluate the total surface area or the number of particles in the collected material. In practice, the conventions will often be used to specify instruments to sample airborne particles for the purpose of measuring concentrations
corresponding to the defined fractions. It should be noted that experimental error in the testing of instruments, and possible dependence on factors other than aerodynamic diameter, mean that it is
only possible to make a statement of probability that an instrument’s performance falls within a certain range, and that different instruments will fall
within an acceptable range.
NOTE The problem of comparing instruments with the conventions is to be dealt with in another standard.
One application is the comparison of mass concentration of airborne size fractions with limit values. It should be noted with respect to relevant European Directives that the use of other methods is allowed provided that they yield the same or stricter conclusion. One important example is the respirable convention in relation to compliance with the limit value. Equipment matching the Johannesburg convention [2] will in practical circumstances give the same or a higher mass concentration (by up to about 20 %) than equipment matching the respirable convention given in 5.3, so the use of equipment matching the Johannesburg convention will be consistent with the European Directive.
The conventions should not be used in association with limit values defined in completely different terms, for example for fibre limit values defined in terms of the length and diameter of fibres.
2 Definitions
For the purposes of this standard, the following definitions apply
sampling convention
A target specification for sampling instruments which approximates to, for each particle aerodynamic diameter:
— in the case of inhalable convention, the ratio of the mass concentration of particles entering the respiratory tract to the corresponding mass concentration in the air before the particles are affected by the presence of the exposed individual and inhalation;
— in the case of the other conventions, the ratio of the mass concentration of particles entering the specified region of the respiratory tract to the mass concentration of particles entering the respiratory tract. (These other conventions can also be expressed as ratios to the mass concentration of total airborne particles.)
2.2
particle aerodynamic diameter
the diameter of a sphere of density I g cm3 with the same terminal velocity due to gravitational force in calm air, as the particle, under the prevailing conditions of temperature, pressure and relative humidity (see clause 4)
NOTE For particles of aerodynamic diameter less than 0,5 pm, the particle diffusion diameter should be used instead of the particle aerodynamic diameter. The particle diffusion diameter means the diameter of a sphere with the same diffusion coefficient as the particle under the prevailing conditions of temperature. pressure and relative humidity.
2.3
inhalable fraction
the mass fraction of total airborne particles which is inhaled through the nose and mouth
NOTE The inhalable fraction depends on the speed and direction of the air movement, on breathing rate and other factors.
2.4
inhalable convention
a target specification for sampling instruments when the inhalable fraction is the fraction of interest
2.5
extrathoracic fraction
the mass fraction of inhaled particles failing to penetrate beyond the larynx
2.6
extrathoracic convention
a target specification for sampling instruments
when the extrathoracic fraction is of interest
2.7
thoracic fraction
the mass fraction of inhaled particles penetrating beyond the larynx
2.8
thoracic convention
a target specification for sampling instruments when the thoracic fraction is of interest
2.9
tracheobronchial fraction
the mass fraction of inhaled particles penetrating beyond the larynx, but failing to penetrate to the unciliated airways
2.10
tracheobronchial convention
a target specification for sampling instruments when the tracheobronchial fraction is of interest
2.11
respirable fraction
the mass fraction of inhaled particles penetrating to the unciliated airways
2.12
respirable convention
a target specification for sampling instruments when the respirable fraction is of interest
2.13
total airborne particles
all particles surrounded by air in a given volume of air
NOTE Because all measuring instruments are size-selective to some extent, it is often impossible to measure the total airborne particle concentration.