Workers’ exposure assessment by inhalation to chemical agents in workplaces could be carried out taking representative measurements and comparing them with occupational exposure limit values (8h - OELV’s and 15 min. – OELV’s)..
NOTE: Different types of occupational exposure limit values (OELV’s) can be used as: legal occupational exposure limits, recommendation of scientific committees, exposure limit values provided by the supplier, etc.
This assessment required a strategy that involves two parts: 1.The initial assessment of worker’s or similar exposure group of workers (SEG) exposure to chemical agents, and 2. The exposure periodic reassessment.
|SEG: SEG: Group of workers having the same general exposure profile for the chemical agent(s) being studied because of the similarity and frequency of the tasks performed, the materials and processes with which they work, and the similarity of the way they perform the tasks.
The final goal of this assessment is to draw conclusions about the compliance of the exposure to the chemical agent with the occupational exposure limit value (OELV), because this will be the key for planning preventive actions.
The INSST introduces this “Calculator” which fulfil the requirements of the standard UNE-EN 689:2019 “Workplace exposure – Measurement of exposure by inhalation to chemical agents – Strategy for testing compliance with occupational exposure limit values”, and allows technicians to estimate workers exposure from representative measurements of chemical agents in workplaces.
For a better understanding and use of the Calculator it is worth stressing the following aspects:
|The LOQ is calculated from the limit of quantification supplied by the laboratory (Loq) divided by the air sampling volume. If the strategy uses different volumes, the highest volume is taken.
- This Calculator allows the worker or SEG exposure assessment by inhalation to one or several chemical agents for compliance with long term OELV’s and short term OELV’s.
- The assessment requires to input, for every chemical agent, the occupational exposure limit value (OELV), the exposure time, the limit of quantification (LOQ) and the concentration and sampling time for every sample and work shift.
- The LOQ only has to be input when results are bellow the LOQ .
- The assessment for compliance with long term OELV’s requires the previous selection of the kind of exposure: 1. Variable exposure: When the concentration of the chemical agent in the environment shows important changes along the work shift. 2. Constant exposure: When the concentration of the chemical agent doesn´t show any important changes along the work shift. The requirements for the total sampling duration are different for both exposure’s types and the Calculator will check in every case they are met, otherwise, a warning will indicate the mistake.
- The assessment for compliance with long term OELV’s requires at least three exposure results of workers belonging to a SEG. The Calculator applies the Preliminary Test, it is sometimes possible to conclude the exposure is on compliance or non – compliance with the OEVL; it is sometimes not possible to reach a decision (Non-decision) and the calculator requires more exposure results (maximum of five) to run again the Preliminary Test; and it is sometimes not possible to reach a conclusion with a Preliminary Test and it will be necessary to carry out additional exposure measurements (until to complete at least a total of six results) in order to apply an Statistical Test.
- The assessment for compliance with short term OELV’s requires a minimum of six exposure results from a SEG. For this type of exposure the Preliminary Test is no suitable and the Statistical Test has to be applied.
- The Statistical Test requires that the exposure results fit a normal or log normal distribution. The Calculator applies the Saphiro-Wilk test for taking the decision to which kind of distribution describes the exposure results better. If the results don’t fit any of these two distributions, the Calculator can’t evaluate the exposure (NO- VALUABLE). This situation could happen because a bad selection of the SEG or for including wrong results.
- If the distribution of exposure results found to be lognormal, the geometric mean (GM) and the standard geometric deviation (GSD) should be used for the exposure assessment. When the distribution of exposure results is normal then the arithmetic mean (AM) and the standard deviation (SD) should be used for the exposure assessment. These parameters have to be calculated from theirs mathematical formulas.
- The situations when, a) exposure results are below the limit of quantification (LOQ) and b) the Statistical Test is required for compliance with OELV assessment, need a minimum of two results above the LOQ and the GM, GSD or AM, SD parameters (depending of the type of distribution) have to be calculated from the regression line of exposure results above the LOQ over z-score .
- The reports contain the following information: 1. Aspects required to identify the assessment carried out (the input of this data is not mandatory). 2. The assessment result (Compliance; Non-Compliance); the values of AM, SD, GM, GSD, UR, UT, UTL95,70, WShapiro-Wilk and Wcritic. 3. Suggestions for periodic reassessment. 4. Graphics. 5. All the input data and the calculated ED, EC and the exposure indexes (I).
The Calculator allows users to save the input data giving a numerical code. This numerical code can be used to retrieve data for future periodic reassessments..
With this Calculator the INSST tries to make easier the exposure assessment to chemical agents to all users, according with the standard UNE-EN 689. Under no circumstances will the INSST take the responsibility for its use.