BS/EN 689-2018 pdf download.Workplace exposure – Measurement of exposure by inhalation to chemical agents – Strategy for testing compliance with occupational exposure limit values.
The sampling duration is also an important factor that can influence the representativeness of exposure measurements. The sampling duration may exceed the OELV reference period if it is necessary to obtain valid and representative measurements in case of extended workshifts (>8 h).
The sampling duration should be chosen to represent the exposure for the task/activity and representatively describe the exposure for the reference period which is assessed (see Annex D). For this purpose the performance characteristics of the measuring procedure shall be taken into consideration.
The sampling duration should be as close to the OELV reference period as it is necessary to determine the average exposure for the reference period, If the total sampling duration is less than the OELV reference period, then the unsampled time should be assessed carefully and critically for exposure changes that have occurred in the unsampled period and that cannot be ignored. Examples of such situations are presented in AnnexD.
For testing compliance with OELV-8 h, three cases shall he considered:
— Ifexposures occur throughout the workshift and the appraiser considers that the workplace factors, including the tasks, are constant during the workshift, the total sampling duration may be shorter than the reference period with a minimum of 2 Ii;
— lithe appraiser considers that the workplace factors, including the tasks, are not constant during the workshift, the total sampling duration shall be longer than 2 h and as close as possible to the shift duration;
— lithe duration of exposure within the workshift is less than 2 h, the sampling duration should cover the whole period of exposure.
When testing compliance with short-term OELV, the sampling duration shall be 15 mm.
Measurements shall be performed on sufficient days and during various specific operations in order to gain insight into the pattern of exposure. It is important to consider different episodes during which exposure conditions can vary (night and day cycles, seasonal variations).
The minimum number of measurements shall be in accordance with £52 and 55.3. The appraiser shall also take into consideration the number of workers belonging to the SEG in order to determine the number of measurements that shall be conducted, to ensure that the results are representative of the whole SEG. This is especially important if workers in a SEG belong to different locations.
The workers chosen for exposure measurement, and the times of measurement, shall be selected so that the measured exposures are representative of the exposure of the workers In the SEG. and this means that it can be necessary to make the measurements at different times. lithe number of measurements to be made is greater than the number of workers in the SEG, it will be necessary to measure some workers more than once. As far as possible, this shall be done to make the measurements representative of the exposures in the SEG.
5.4 Validation of results and SEGs
5.4.1 General
Before testing compliance with the OEL.V it Is necessary to consider the validity of each measurement and to use the measurements to evaluate the constitution of the SEG for testing compliance as explained in £5.
5.4.2 ValidatIon of measurement results
When the measurement results are available, each measurement shall be evaluated using the information collected during measurement, and by comparison with the other measurements of the SEG.
If the result Is unusually high or low, the possibility that this is because of errors of sampling or analysis shall be considered, and if this is the case then the result shall be excluded. However, before excluding a measurement, appraiser notes, and/or contextual information shall be used to identify measurements for which accidents with equipment or malfunctions, or deliberate misuse have occurred in relation to the activity, sampling or analysis. If no such irregularity can be reliably identified, the measurement shall not be excluded. If measurements are excluded, it may be necessary to repeat measurements to have sufficient representative measurements to compare with the OELV.
Any removal of results and the reasons shall be explicitly described in the report.
5.4.3 ValIdation of SEGs
After results have been accepted, they shall be used to validate the constitution of each SEG. Based on expert judgernent and information collected during the measurements and the basic characterization, the appraiser shall be able to confirm the constitution of SEGs. When the number of valid measurements is at least 6, the distribution of results shall be examined.
Exposure measurements are usually log normally distributed. To check whether all individuals belong to the same SEG, and whether the distribution of measurements is log-normal, the log probability plot of the data shall be analysed. Guidance is given in AnnexE
An Important complication Is that two workers doing the same job may not have the same exposure. This phenomenon, known as between-worker variability, means that measurements of one worker’s exposure cannot simply be assumed to apply to others doing nominally the same job. Furthermore, exposure varies from shift to shift, giving rise to within-worker variability.
If the measurements show that one or more workers have exceptional exposure, which seems inconsistent with the distribution of results from the rest of the SEG, the reasons shall be investigated and these workers may be treated separately, for example forming a new SEG and taking more measurements as necessary. Guidance is given in Annex E. It may be necessary to repeat exposure measurements to have sufficient representative measurements for each SEG to test compliance.BS/EN 689-2018 pdf download.