12. Monitoring in the workplace
12.1 General principles
12.1.1. Employers should monitor and record the exposure of workers to hazardous chemicals to ensure their safety and health. They should ensure that workers are not exposed to chemicals to an extent which exceeds exposure limits or other exposure criteria for the evaluation and control of the working environment. Based on the monitoring data, employers should assess the exposure of workers to hazardous chemicals.
12.1.2. Airborne concentrations of hazardous chemicals should be measured in all places of work where this is necessary to ensure the safety and health of workers against inhalation risks.
12.1.3. Measurements of airborne contaminants are necessary if other techniques do not suffice to provide a valid estimate of the risk of exposure and to assess the existing control measures.
12.1.4. Techniques for this risk assessment may include the following: information on the intrinsic health and physical hazards, obtained from the chemical safety data sheets; estimation of exposure based on the method of work and work pattern; advice from the supplier; experience of exposure in the workplace or of other users; and simple qualitative tests. Simple qualitative tests include, where appropriate, the use of smoke tubes or pellets to determine ventilation characteristics, and of the dust lamp for illuminating dust emissions.
12.1.5. The need for a programme for the measurement of airborne contaminants should be based on the factors listed in paragraph 12.1.4, the extent of the exposure of workers established as a result of the measurements taken, and the reliance on, and the consequent need to check the effectiveness of, engineering control measures. Where the need for a programme of measurements is determined for certain hazardous chemicals, the monitoring strategy should be followed.
12.2 Measuring methods
12.2.1. Sampling equipment should be compatible with the analytical methods available and should have been validated over a suitable range of concentrations above and below the exposure limits or other exposure criteria in accordance with published national or international standards. where they exist.
12.2.2. Static monitoring should be used to determine the distribution of an airborne chemical throughout the general atmosphere of the working area and to identify problems and priorities. Air samples should be taken:
(a) close to sources of emission in order to evaluate concentrations or the standard of engineering controls;
(b) at various places in the working area to assess the extent of the chemical's general distribution; and
(c) from working areas which represent typical exposure.
12.2.3. Personal monitoring should be used to evaluate the risk of exposure to the individual worker. Air samples should be collected in the workers breathing zone by means of personal samplers. Sampling should be carried out while the work activity is in operating.
12.2.4. Where concentratiOns vary from one work operation or phase to another, personal sampling should be done in such a manner that the averages and in any case the maximum, level of exposure of each individual worker can be determined.
12.2.5. Personal sampling should measure exposure, or allow assessment of exposure throughout the work shift. The exposure should be compared to occupational exposure limit values, which are usually quoted for an eight-hour period or, for short-term limits, 15 minutes. The measurement may be continuous over the whole shift or intermittent, so long as this allows a valid calculation of the average exposure and where necessary is supplemented by short-term sampling during periods of peak emission.
12.2.6. Exposure profiles of particular jobs or occupational categories should be constructed from the air-sampling data of different operations and from the workers' exposure time in these jobs.
12.3 Monitoring strategy
12.3.1. Where a systematic measurement programme has been decided, it should evaluate whether the exposure of workers to certain hazardous chemicals prescribed by the competent authority or determined by the initial assessment is being kept under control.
12.3.2. The aims of this programme should be:
(a) to ensure that the health of the workers is efficiently protected;
(b) to ensure that the preventive actions which have been taken are still effective;
(c) to ensure that the levels, as measured previously, remain unchanged or fall;
(d) to ensure that any changes made in manufacturing processes or work practices will not lead to an excessive exposure to hazardous chemicals;
(e) to promote the implementation of more efficient preventive measures.
12.3.3. The monitoring of airborne concentrations of chemicals in the working environment should be performed only by skilled personnel with adequate equipment and technical training.
12.3.4. The employer should arrange for regular inspection, maintenance and calibration of the measuring equipment.
12.3.5. The service responsible for monitoring the working environment should be kept informed about any change in plant, equipment, process, materials or work practices likely to bring about any substantial alteration in levels of exposure to hazardous chemicals.
12.4 Record keeping
12.4.1. Records should be kept by employers on measurements of airborne hazardous chemicals. Such records should be clearly marked by date, work area and plant location.
12.4.2. Personal sampling measurements, including the exposures calculated, should be recorded.
12.4.3. The workers and their representatives, and the competent authority, should have access to these records.
12.4.4. Besides the numerical results of measurements, the monitoring data should include, for example:
(a) the marking of the hazardous chemical;
(b) the location, nature, dimensions and other distinctive features of the workplace where static measurements were made; the exact location at which personal monitoring measurements were made, and the names and job titles of the workers involved;
(c) the source or sources of airborne emissions, their location and the type of work and operations being performed during sampling;
(d) relevant information on the functioning of the process, engineering controls, ventilation and weather conditions with respect to the emissions;
(e) the sampling instrument used, its accessories and the method of analysis;
(f) the date and exact time of sampling;
(g) the duration of the workers' exposure, the use or non-use of respiratory protection and other comments relating to the exposure evaluation;
(h) the names of the persons responsible for the sampling and for the analytical determinations.
12.4.5. Records should be kept for a period of time determined by the competent authority. Where this has not been prescribed, it is recommended that the employer keep the records, or a suitable summary, for:
(a) at least 30 years where the record is representative of the personal exposures of identifiable employees;
(b) at least five years in all other cases.
12.5 Interpretation and application of monitoring data
12.5.1. The risk of exposure should be assessed on the basis of the numerical results obtained, supported and interpreted in the light of other information such as length of exposure, work procedures and patterns, measurements of ventilation performance and other particular circumstances of work during measurement.
12.5.2. In the event that monitoring discloses levels which are in excess of the exposure limits, employers should inform the workers and their representatives, in a manner which is easily understood by the workers, of the risk and of the action to be taken to reduce this as part of the action programme.
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