1、CEN EN*b89 75 3404589 0322834 249 B in each of these stages different job functions may be necessary and be subject to different exposure conditions. Distance to emission sources and physical parameters such as rates of release, air current, meteorological variations, have also a profound influence.
2、 The resulting variability of exposure conditions is made even greater by individual practices. All this explains why rapid fluctuations in contaminant concentration or large variations over very small distances are commonplace: site, moment and duration of sampling are decisive. Some measurements o
3、n a given day or period may give an insufficient view of the actual variability of individual polluted-air exposure characteristics. The sampling equipment often introduces its own limitations, sometimes critical, as in aerosol fractions assessments, and the analytical steps add further difficulties
4、 or uncertainties, e.g. insufficient identification or separation of chemical species, or interferences. In this complex context, sampling strategy is responsible for representativeness at the lowest possible cost. In this variety of situations and difficulties, assessments may be undertaken with ve
5、ry different motives, purposes, and practices. Schemes and guidelines are offered to harmonize basic concepts and actions. In order to guarantee the quality of assessments and, if necessary, to improve work conditions, professional judgment has to be exercised. 1 Scope This European Standard gives g
6、uidance for the assessment of exposure to chemical agents in workplace atmospheres. It describes a strategy to compare workers exposure by inhalation with relevant limit values for chemical agents in the workplace and measurement strategy. 2 Normative references This European Standard incorporates b
7、y dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions Page 3 EN 689: 1995 of any of these publications apply t
8、o this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies. EN 482 Workplace atmospheres - General requirements for the perfmance of procedures for the measurement of chem.ica1 agents 3 Definitions
9、For the purpose of this European Standard the following definitions apply. 3.1 exposure The presence of a chemical agent in the air within the breathing area of a worker. It is described in terms of concentration of the agent as derived from exposure measurements and referred to the same reference p
10、eriod as that used for the limit value. 3.2 chemical agent Any chemical element or compound, on its own or admixed as it occurs in the natural state or as produced by any work activity, whether or not produced intentionally and whether or not placed on the market. 3.3 work pattern The definable seri
11、es of activities from the periods under consideration. 3.4 workplace The workplace is the defined area or areas in which the work activities are carried out. 3.5 limit value Reference figure for the concentration of a chemical agent in air. NTE. Limit values are mostly set for reference periods of 8
12、 h, but may also be set for shorter periods or concentration excursions. The limit values for gases and vapours are stated in terms independent of temperature and air pressure variables in ml/mJ (ppm VIV) and in terms dependent on those variables in mum3 for a temperature of 20 OC and a pressure of
13、101,3 kPa. The limit values for suspended matter are given in mg/m3 or multiples of that for actual environmental conditions (temperature, pressure) at the workplace. The limit values of fibres are given in fibres/m3 or fibres/cm3 for actual environmental conditions (temperature, pressure) at the wo
14、rkplace. 3.6 reference period The specified period of time stated for the limit value of a specific agent. The reference period for a long term limit is normally 8 h and for short term limit normally 10 min to 15 min. 0 BSI 1996 CEN EN*b89 95 U 3404587 0122841 489 Page 4 EN 689 : 1995 3.7 personal s
15、ampler (or personal sampling device) A device attached to a person that samples air in the breathing area. 4 General The strategy includes two phases: - an occupational exposure assessment (OEA): the exposure is compared with the limit value; - periodic measurements (PM) to regularly check if exposu
16、re conditions have changed. The occupational exposure assessment is applied for the first evaluation and repeated after any significant change in working conditions, industrial process, products or chemicals or limit value. In this first phase no formal scheme of evaluation has to be followed, but i
17、t is left open to the professional judgment of the user to interpret and apply the guidelines. In the second phase, the frequency of the periodic measurements depends on the result of previous measurements. The requirement for future periodic measurements should have been established as a result of
18、the initial OEA or subsequent amendments to it. These requirements include the scope and frequency of measurements to be made. The periodic measurements follow a procedure which is defined in the occupational exposure assessment. In certain cases the periodic measurements can be omitted. Figure 1 gi
19、ves a schematic overview of the procedures described in this European Standard. 5 Occupational exposure assessment 5.1 Assessment strategy 5.1.1 General The workpattern and workplace under consideration have to be described within the occupational exposure assessment. The occupational exposure asses
20、sment comprises three steps: - identification of potential exposure (list of substances); - determination of workplace factors; - assessment of exposures. 5.1.2 Identification of potential exposure The preparation of a list of all chemical agents in the workplace concerned is an essential first step
21、 to the identification of the potential for hazardous exposure. The list includes, as far as any of them can contribute to exposures, primary products, impurities, intermediates, final products, reaction products and byproducts. Appropriate limit values have to be obtained and where these are not av
22、ailable other criteria may be used for the purpose. In the case of a process not yet in operation this identification may be partially carried out by using relevant available data but such identification WU need to be confirmed at a later stage. 5.1.3 Determination of workplace factors In this step
23、the work processes and procedures are evaluated to gauge the potential for exposure to chemical agents by a detailed review of, for example: - job functions: i.e. tasks; - work patterns and techniques; - production processes; - workplace configuration; - safety precautions and procedures; - ventilat
24、ion installations and other forms of engineering control; - emission sources; - exposure times; - workload. 5.1.4 Assessment of aposum An assessment of exposures which brings together the identification of potential exposures, the workplace factors and the links between them, requires a structured a
25、pproach and may be conducted in three stages: - an initial appraisal; - a basic survey; - a detailed survey. For the comparison with the limit value the data about temporal and spatial distribution of the concentrations of the substances in the workplace air have to be collected. However, it is not
26、necessary to use every stage of the assessment. If it is expected that exposure exceeds the limit value or if it is clearly determined that exposure is well below the limit value, then the occupational exposure assessment can be concluded and action taken in accordance with 5.5. O BSI 1996 CEN EN+b8
27、7 75 U 340Y587 0322842 335 Page 5 EN 689: 1995 Identlly potenilal exposure (see 5.1.2) Delermlne workplace factors (see 5.1.3) I I tnltlal appraisal of exposure (see 5.1.4.1) I Can the presence 01 agents In the air be ruled out for Cerlaln ? I no Conduct basic survey (see 5.1.4.2) I Y 85 Exposure ab
28、ove Ilmll value? I Exposure well below Ilmlt value and remaining so on a long term basls? I conduct detailed survey (see 5.1.4.3) 1 Exposure above limit vatue? I Exposure well below Ilmlt value and remaining so on a long term nasls? n O-/ Perlodlc measurements necessary ? I Y es Estaniish scheme tor
29、 periodic measurements (see ciause 6) + Perform periodlc measurements I Y es Exposure above Ilmlt value? I no Exposure well nelow limit value and remaining so on a long ierm basis? Report (see ciause 7) I no r I Figure 1. Schematic overview of procedure O BSI 1996 _ CEN EN*b89 95 340458% 0322843 251
30、 E Page 6 EN 689 : 1995 5.1.4.1 Initial appraisal The initial appraisal, by referring to the list of chemical agents (see 5.1.2) and the workplace factors (see 5.1.3) yields a consideration of the likelihood of exposure. The variables affecting the airborne concentrations of substances close to an i
31、ndividual are: - the number of sources from which agents are released; - the production rate in relation to production capacity; - the rate of release from each source; - the type and position of each source; -the dispersal of the agents by air movement; - the type and effectiveness of exhaust and v
32、entilation systems. The variables related to the individuals actions and behaviour are: - how close the individual is to the sources; - length of time spent in an area; - the individuals own work practices. If this initial appraisal shows that the presence of an agent in the air at the workplace can
33、not for certain be ruled out this agent needs further consideration (see 5.1.4.2 and 5.1.4.3). 5.1.4.2 Basic survey The basic survey provides quantitative information about exposure of workers concerned, taking particular account of tasks with high exposures. Possible sources of information are: - e
34、arlier measurements; - measurements from comparable installations or workprocesses; - reliable calculations based upon relevant quantitative data. If the information obtained is insufficient to enable valid comparison to be made with the limit values, it has to be supplemented by workplace measureme
35、nts. 5.1.4.3 Detailed surmey The detailed survey is aimed at providing validated and reliable information on exposure when this is close to the limit value. 5.2 Measurement strategy Generally, for the purposes of obtaining quantitative data on exposures by measurement, an approach should be taken wh
36、ich enables the most efficient use of resources. Where it is suspected that exposure levels are well below or above the limit values, these clear cases may be confirmed by the use of techniques which are easily applied and which may be less accurate. Other possibilities may be worst case measurement
37、s, sampling near emission source or screening measurements (see 4.2 to 4.4 of EN 482 : 1994). Thus, in these cases, the occupational exposure assessment may often be completed without further investigation. In other cases, where exposures are suspected to be close to the limit values, then it will b
38、e necessary to undertake a more accurate investigation, making full use of the capabilities of instrumental and analytical techniques, where appropriate (see 4.5 of EN 482 : 1994). 5.2.1 Selection of workers for exposure measurements It is not possible to be precise as to the procedure for selection
39、 of a worker or group of workers for exposure measurements. However, some general guidelines can be given. One possible approach is to sample workers randomly from within the whole exposed population. However, from a statistical standpoint this requires a relatively large number of samples. In many
40、workplaces if this approach is used there is a considerable risk that small subgroups of highly exposed personnel will be missed. The preferred approach is to subdivide the exposed population into homogeneous groups with respect to exposure. The variability of exposure levels is smaller for well-def
41、ined groups than for the exposed workforce as a whole. Thus, where a group of workers is performing identical or similar tasks at the same place and has a similar exposure, sampling such as representative of the group may be carried out within that group. Groupings have the practical advantage that
42、resources can be concentrated on those groups of workers with the highest exposure. It is necessary to verify that groups have been properly selected by critical study of the work patterns and examination of the preliminary sampling data. Within a homogeneous group exposure patterns will still be su
43、bject to both random and systematic variations. Professional judgment as to the homogeneity of the defined groups is essential. However, as a rule of thumb, if an individual exposure is less than half or greater than twice the arithmetic mean, the relevant work factors should be closely re-examined
44、to determine whether the assumption of homogeneity was correct. Professional judgment is also required when deciding on sample size, particularly when small groups are concerned. However, as a general rule, sampling should be carried out for at least one employee in ten in a properly selected homoge
45、neous group. The frequency at which trials should be made and the number of group members selected for measurements will depend on how accurate the estimates of the distribution parameters such as the O BSI 1996 CEM EN*bA9 95 348458% QI122844 198 mean and variance need to be, on how far exposures ar
46、e below the limit value, and the significance of the prevailing exposure levels and the properties of the substances. Where the arithmetic mean of exposure measurements is close to half of the limit value it is likely that some results will exceed the limit value. If exposure is characterized by pea
47、k exposures, then these peaks have to be assessed according to the short term limit requirements, if any. 5.2.2 Fixed-point measurements Fixed-point measuring systems may be used if the results make it possible to assess exposure of the worker at the workplace. Samples should as far as possible be t
48、aken at breathing height and in the immediate vicinity of workers. If in doubt the point of greatest risk is to be taken as the measuring point. 5.2.3 Selection of measurement conditions 5.2.3.1 - the sampling procedure; - the analytical procedure; - the sampling location(s); - the duration of sampl
49、ing; - the timing and the interval between measurements; - the calculations which yield the occupational exposure concentration from the individual analytical values see annex B); - further technical instructions concerning the measurements; - the jobs to be monitored. O BSI 1996 CEN ENxb89 95 3404589 0322845 024 Page 8 EN 689 : 1995 5.4 Exposure to mixtures If workers are exposed simultaneously or consecutively to more than one agent, this fact needs to be taken into consideration. 5.5 Conclusion of the occupational exposure assessment The occupational exposure concentrat
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