Rischio chimico: metodo di valutazione EN 689:2019
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Rischio chimico: metodo di valutazione EN 689:2019 ID 8634 | 08.10.2020 La norma EN 689:2019 rispetto all'Ed. 2018 (EN 689:2018), della quale è stato proposto un Documento di approfondimento nel 2018, include il corrigendum AC:2019 che modifica le abbreviazioni, il contenuto in molti allegati, la bibliografia e i riferimenti riportati. Nel documento allegato tutte le modifiche apportate nella Ed. 2019 sono indicate in blu. Data entrata in vigore: 16 maggio 2019 Recepisce: EN 689:2018+AC:2019 Sostituisce: UNI EN 689:2018 Il documento allegato estratto della nuova norma EN 689:2019 (allegati A, B, C, D, E, F, G, H); la norma è una delle metodiche standardizzate per la misurazione degli agenti contenute nell’ALLEGATO XLI del D.Lgs.81/08 - Titolo IX art.225 c.2. La norma europea EN 689:2019 tratta dei metodi per la misurazione dell’esposizione agli agenti chimici sul luogo di lavoro ed, in particolare, delle strategie per la misurazione ed il confronto dei risultati con i valori limite di esposizione professionale (OELVs). La valutazione dell’esposizione e la dichiarazione certa del non superamento dei limiti di esposizione professionale richiederebbero una misura giornaliera dell’esposizione per ogni singolo lavoratore. Questo tipo di approccio è possibile per le radiazioni ionizzanti, ad esempio, ma non lo è per gli agenti chimici a causa di alcuni limiti delle tecniche di misura e dei costi delle misure stesse. La norma EN 689:2019 dà la possibilità al Datore di Lavoro di utilizzare un numero di misure ridotte per dimostrare con un elevato grado sicurezza che è improbabile che i lavoratori siano esposti a valori superiori ai valori limite. Per ridurre il numero di misurazioni i campioni di aria vengono raccolti all’interno di gruppi simili di esposizione (SEGs). In questo modo una singola misurazione o diverse misurazioni inferiori ai limiti possono essere sufficienti a dimostrare in modo affidabile la conformità senza l’uso di test statistici. Metodiche standardizzate misurazione degli agenti D.Lgs.81/08
... http://store.uni.com/catalogo/index.php/uni-en-689-2019.html Il presente documento è un estratto degli allegati della norma tecnica EN 689:2019. _____ Excursus Annex A (informative) Assessment of exposure A.1 General This annex gives guidance on when measurements are advisable or if other approaches of assessment maybe used. In practice there are different ways of assessing workers' exposure to chemical agents. This annex is intended as a support to the identification and assessment of inhalation exposure on workplaces. In assessment, it may be necessary to consider together all activities in a working area, which is the spatially or organisationally delimited part of a site in which activities involving chemical agents are carried out by one or more workers and can be brought together in a risk assessment. It may encompass one or more workplaces or working processes. The main factors to be used to choose the appropriate method for assessing exposure are extensive, including the type and duration of exposure by inhalation at workplaces. In addition to exposure measurements, the methods used to assess exposure generally include: reasonable - worst-case measurements (under control); Reasonable worst-case measurements are performed to estimate the maximum exposures likely to occur with the controls in place. When applying one of these methods and there is still uncertainty concerning the identification result and its evaluation, additional workplace measurements are recommended. In A.2 to A.9 different workplace situations are described together with information about possible methods to assess exposure and to derive suitable protective measures. Table A.1 gives an overview of workplace situations addressed in this Annex and the recommended way of exposure assessment. ... Annex E Check of exposure measurements distribution, and identification of exceptional exposure within the SEG E.1 General Annex E gives graphical and statistical methods for the validation of the results and the SEGs, as required in 5.4, for the identification of individuals or groups whose exposure is not properly represented by the SEG, and for the decision to use the normal or the lognormal distribution in the compliances test (see Annex F). The graphical method supports the identification of a LOQ (see Annex H) and is applied using at least six exposure measurements in the SEG. The measurement results may be examined to see if a normal or lognormal distribution fits the results better. In many circumstances, exposure variability is influenced by the multiplicative interactions of workplace factors (see 5.1.3, Annex A and Annex D). Measurements would be expected to approximate to a lognormal distribution, and this has often been observed. However, a normal distribution may appear with high control of workplace factors in constant conditions (see A.2) or if the influence of workplace factors is outshined by the random variation in the measuring procedure (see 5.2.2). The shape of the measurement results may be examined by a statistical test, such as the Shapiro and Wilk test, to see whether their distribution is closer to lognormal than normal distributions. For example, the results may first be tested as to whether their distribution fits a normal distribution. This will give a probability P1 of the hypothesis that the normal distribution fits the results. The test may then be repeated using the logarithms of the results, giving a probability p2. If p1 > p2 it may be concluded that a normal distribution fits the results better than a lognormal distribution. The result of comparing p1 and p2 determines the distribution to be used for the compliance test (see Annex F). The appraiser should take into account that the exposure distribution may deviate in the tails from the (log)normal model (see E.2.3) and that the normal distribution does not exclude negative concentrations. Truncation at higher concentrations (vapour saturation, explosion limit or maximum dustiness) can occur, like censoring in the lower tail due to the increasing number of results below the LOQ. Therefore, the check on the distribution and on pooling results are important before LOQ adjustment (see Annex H) and applying the models in the compliance test (see 5.5.3 and Annex F). E.2 describes a graphical method for a lognormal distribution. To decide if a normal distribution describes the results better, the procedure should be repeated using normal probability paper. E.3 refers to software that automates the graphical method of E.2, test goodness-of fit (see E.2.2) and test the consistency of the SEG (see E.2.4.3). E.2.4.2 SEG consisting if two groups Figure E.2 illustrates a log-probability plot which appears to be two intersecting straight lines rather than a single one. These measurements were divided into two different groups (with the central point in each, as this result could be in either group), and the two sets plotted separately on the same chart in Figure E.3. Figures E.2 and E.3 suggest that the SEG includes two different groups with different exposure patterns, and the SEG should be divided in two, and more exposure measurements made so that the number of measurements in each SEG reaches the minimum required by the statistical test chosen in 5.5.3. If these extra measurements are added to the original plot, modifying Figure E.2, they may clarify whether one or two distributions are present, or if there is some other explanation.
Key X exposure xk (mg/m3) Figure E.2 - Example of exposure measurements which appear to come from two different populations within the SEG, each with a lognormal distribution of exposure
Key X exposure xk (mg/m3) Figure E.3 - Exposure measurements replotted as two different sets (with the central point included in both), confirming that these appear to be two different lognormally-distributed populations[/panel] _______ Indice Premessa Fonte: UNI Certifico Srl - IT | Rev. 1.0 2019 Collegati: |
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