Division II Countable fibres method

United Kingdom

Where fibre counting procedures are used for the purpose of checking compliance with the limit value in Article 4 of the Directive, subject to the provisions of Article 6 (3) of the Directive, a conversion factor of two fibres/ml to 0,1 mg/m³ of asbestos dust may be used.

For the purposes of the Directive a fibre is defined as any object of length greater than 5 μm, breadth less than 3 μm, and having a length/breadth ratio greater than 3/1, which is countable by phase contrast optical microscopy using the European reference method defined in Annex I of Directive 83/477/EEC.

A fibre counting method shall meet the following specifications:

1..

The method shall be capable of measuring the concentration of countable fibres in the emitted gases.

The controlling authority shall decide on the periodicity of such measures, according to the characteristics of the plant and of its production, but this should be at least every six months. Where periodical measures are not taken, the limit value specified in Article 4 applies to the total dust emission.

Sampling shall be conducted before any dilution of the flow to be measured.
2..

Operation of the installation

Measurement shall only be valid if sampling takes place while the installation is operating normally.
3..

Selecting the sampling point

Sampling shall take place at a point where there is a laminar flow of air. As far as possible, care shall be taken to avoid turbulence and obstacles which might disrupt the flow of air.
4..

Modifications required for sampling

Suitable apertures shall be made in ducts where sampling is to take place, and proper platforms shall be provided.
5..

Measurements to be taken before sampling

Before sampling commences, it is first necessary to measure air temperature and pressure, and the velocity of flow in the duct. Air temperature and pressure shall normally be measured along the sampling line at normal flow rates. Under exceptional conditions, it is also necessary to measure the water vapour concentration so that the results can be amended accordingly.
6..

General requirements of the sampling procedure

The procedure requires a sample of air from a duct carrying the emissions of asbestos dust to be drawn through a filter, and the countable asbestos fibres in the dust retained on the filter to be measured.
6.1..

The sampling line shall first be checked to ensure that it is airtight, and that there are no leaks which might give rise to measurement errors. The sampling head shall be carefully sealed off and the sampling pump started up. The rate of leakage shall not exceed 1 % of the normal sampling flow.
6.2..

Sampling of the emitted gases shall be conducted inside the emission duct under isokinetic conditions.
6.3..

Duration of sampling shall depend on the type of process being monitored and the size of the sampling nozzle used. The sampling period shall be sufficient to ensure that the sample collection filter carries between 100-600 countable asbestos fibres/mm². It shall be representative of the full process being monitored.
6.4..

The sampling head and the number of points where samples must be taken shall be determined in accordance with the national standard adopted.
7..

Nature of the sampling collection filter
7.1..

The filter appropriate to the technique of measurement shall be chosen. For the countable fibre method, membrane filters (mixed esters of cellulose or cellulose nitrate) of nominal pore size 5 μm, with printed squares and a diameter of 25 mm shall be used.
7.2..

The sample collection filter shall have a minimum filtration efficiency of 99 % with respect to countable asbestos fibres.
8..

Counting of fibres

The fibre counting method shall conform to the European reference method, as set out in Annex I of Directive 83/477/EEC.
9..

Expression of results

In addition to measurement data, results shall record temperature, pressure and flow data and shall include all relevant information, such as a simple diagram showing the location of sampling points, the dimensions of ducts, the volumes sampled and the market of calculation used to obtain the results. These results shall be expressed at normal temperature (273 K) and pressure (101,3 kPa).