Objectives of monitoring
3.97.
The general term ‘monitoring’ refers to a process that includes the making of measurements in relation to the assessment or control of exposure to radiation and exposure due to radioactive materials. Although measurements play a major part in any monitoring programme, monitoring is more than simply measurement; it requires interpretation and assessment. The primary justification for making a measurement should therefore be expressed in terms of the way in which it helps to achieve and demonstrate adequate protection and safety, including in the optimization process.
3.98.
A programme of monitoring may serve various purposes, depending on the nature and extent of the practice. These purposes can include the following:
Assessing the exposure of workers and demonstrating compliance with regulatory requirements.
Confirming the effectiveness of working practices (e.g. the adequacy of supervision and training) and engineering standards.
Determining the radiological conditions in the workplace, whether these are under adequate control and whether operational changes have improved or worsened the situation.
Evaluating and improving operating procedures from a review of the collected monitoring data for individuals and groups. Such data may be used to identify both good and bad features of operating procedures and design characteristics, and thereby contribute to the development of safer working practices in relation to radiation.
Providing information that can be used to enable workers to understand how, when and where they are exposed, and to motivate them to take steps to reduce their exposure.
Providing information for the evaluation of doses in the event of accidental exposures.
Furthermore, monitoring data may be used for the purpose of risk–benefit analysis and to supplement medical records.
3.99.
Monitoring can provide important supplementary benefits in the fields of industrial relations or public relations (such as reassurance and motivation of the workforce) or of scientific investigation (such as data for epidemiological studies), or in providing information useful in the determination of liability in the event of the expression of adverse health effects in individual workers. These considerations may affect decisions about the nature and extent of monitoring programmes, but they do not in themselves provide the primary justification for a monitoring programme for protection and safety.
Monitoring programme
3.100.
The principal responsibility for setting up a monitoring programme rests with the management. The monitoring programme should be designed in consultation with an appropriate qualified expert on the basis of the prior radiological evaluation discussed in paras 3.53–3.59, with due account being taken of regulatory requirements.
3.101.
Monitoring programmes can be divided and subdivided into several different types. The first division relates to the objectives of the monitoring. At this level, four types of monitoring can be defined for the purposes of radiation protection:
Routine monitoring is associated with continuing operations and is intended to meet regulatory requirements and to demonstrate that the working conditions, including the levels of individual dose, remain satisfactory.
Special monitoring is investigative in nature and typically covers a situation in the workplace for which insufficient information is available to demonstrate adequate control. It is intended to provide detailed information to elucidate any problems and to define future procedures. It should normally be undertaken at the commissioning stage of new facilities, or following major modifications to facilities or procedures, or when operations are being carried out under abnormal circumstances, such as an accident.
Confirmatory monitoring is performed where there is a need to check assumptions made about exposure conditions (e.g. to confirm the effectiveness of protective measures).
Task related monitoring applies to a specific operation. It provides data to support the immediate decisions on the management of the operation. It may also support the optimization of protection.
3.102.
Each of these types of monitoring programme can be subdivided on the basis of the location of the monitoring:
Individual monitoring comprises measurements made using equipment worn by individual workers, or measurements of quantities of radioactive substances in or on their bodies, and the interpretation of such measurements.
Workplace monitoring comprises measurements made in the working environment and the interpretation of such measurements.
3.103.
Individual monitoring can be further subdivided into monitoring for external exposure, for internal exposure and for skin contamination. Workplace monitoring can be further subdivided into monitoring for external radiation, for air contamination and for surface contamination. The details of the programmes will be influenced by factors such as the type and energy of the radiation and the radionuclides involved (see Section 7).
3.104.
The programme design should reflect the objectives of the monitoring programme, and these should be clearly specified and recorded. The design should include the basis for the interpretation of the monitoring results and how this relates to the objectives of the programme, and this basis should be recorded. A distinction should be made in the programme between monitoring for the purpose of controlling operations and monitoring for the formal assessment of exposure to meet regulatory requirements.
3.105.
The equipment to be used in the monitoring programme should be suitable for the types of radiation and the forms of radioactive material encountered in the workplace. The equipment should be calibrated to meet appropriate standards. More detailed guidance, including guidance on the provision of approved dosimetry services, is presented in Section 7. Guidance on the management system for dosimetry service providers is given in Section 8.
3.106.
The design and implementation of a monitoring programme should conform to the quality assurance requirements embodied in the management system to ensure that procedures are established and followed correctly and to ensure that records are promptly compiled and correctly maintained. The design of the monitoring programme should indicate the records that should be kept, and the associated procedures for keeping and discarding records. All of these aspects should be reviewed regularly, at predetermined intervals or following any major change in operations of the installation or in regulatory requirements. The purpose of such reviews should be to ensure that the monitoring effort (type, frequency and extent) is appropriately employed. The information should also be used to identify both good and bad features of operating procedures, and both good and bad design characteristics.
Individual monitoring
3.107.
The need for, and appropriateness of, individual monitoring of workers will depend on factors such as the following:
The amount of radioactive material present and the radionuclides involved;
The physical and chemical form of the radioactive material;
The type of containment used;
The operations performed;
The expected levels and likely variations in the doses or intakes;
The complexity of the measurement procedures and interpretation procedures of the measurement programme;
The general working conditions.
For example, workers involved in the handling of sealed sources (or dispersible sources that are in closed containers with or without shielding) may need to be monitored for external exposure but not for internal exposure. Conversely, workers handling radionuclides such as 3H, 125I or 239Pu may need to be monitored for internal exposure but not for external exposure.
3.108.
The need for individual monitoring is likely to be greater in the early stages of an operation. As experience in the workplace is accumulated, the need for routine individual monitoring can be kept under review to decide on the need for continuation of individual monitoring or whether workplace monitoring is sufficient for radiation protection purposes. In determining the necessity for individual monitoring, consideration should also be given to the potential for accidental exposures.
3.109.
For work involving internal exposure, the decision to register a worker in an individual monitoring programme should be based on the likelihood of an intake of radionuclides in excess of a predetermined level. If operational procedures need to be set up to prevent or reduce the possibility of an intake, a controlled area should, in general, be established. Individual monitoring for intakes of radionuclides should be used routinely only for workers who are employed in areas that are designated as controlled areas specifically in relation to the control of contamination and in which there are grounds for expecting significant intakes. If experience has shown that it is unlikely that committed effective doses from occupational exposure due to annual intakes of radionuclides would exceed 1 mSv, then individual monitoring may be unnecessary, but workplace monitoring should be undertaken. The following activities are examples of those for which routine individual monitoring for internal exposure should be considered:
The handling of large quantities of gaseous or volatile materials, for example of tritium and its compounds in large scale production processes, in heavy water reactors and in manufacturing of gaseous light sources;
The processing of plutonium and other transuranic elements;
The maintenance of reactor facilities, which can lead to exposure due to fission products and activation products;
The bulk production of radioisotopes;
The production and handling of large quantities of radiopharmaceuticals, such as 18F for diagnostics by positron emission tomography or 131I for therapy;
The mining of high grade uranium ores, processing of uranium mineral concentrates and production of nuclear fuel;
The processing of mineral concentrates, such as monazite that is rich in thorium, and the production of products containing thorium.
3.110.
To obtain the necessary accuracy and precision, individual dosimetry should be performed, whenever possible, by an approved dosimetry service. The regulatory body should give consideration to the establishment of a national accreditation procedure as a basis for the approval of dosimetry services. The management system for dosimetry service providers is discussed in Section 8.
3.111.
For visitors making short and infrequent visits to controlled areas, individual monitoring may be performed but is not necessarily required. However, a record of the radiological conditions in the controlled areas visited (e.g. data from workplace monitoring or from individual monitoring of the visitors’ escort) and the length of time spent in these areas during the visits should be retained.
Workplace monitoring
3.112.
The requirements for workplace monitoring are set out in paras 3.96–3.98 of GSR Part 3 [2], which state that:
“3.96. Registrants and licensees, in cooperation with employers where appropriate, shall establish, maintain and keep under review a programme for workplace monitoring under the supervision of a radiation protection officer or qualified expert.
“3.97. The type and frequency of workplace monitoring:
Shall be sufficient to enable: (i) Evaluation of the radiological conditions in all workplaces; (ii) Assessment of exposures in controlled areas and supervised areas; (iii) Review of the classification of controlled areas and supervised areas.
Shall be based on dose rate, activity concentration in air and surface contamination, and their expected fluctuations, and on the likelihood and magnitude of exposures in anticipated operational occurrences and accident conditions.
“3.98. Registrants and licensees, in cooperation with employers where appropriate, shall maintain records of the findings of the workplace monitoring programme. The findings of the workplace monitoring programme shall be made available to workers, through their representatives where appropriate.”
3.113.
The programmes for monitoring the workplace should specify: (a) The quantities to be measured; (b) Where and when the measurements are to be made, and at what frequency; (c) The most appropriate methods and procedures for measurement; (d) Investigation levels and the actions to be taken if they are exceeded.
3.114.
The results and findings of workplace monitoring should be recorded and should be made available to the management and to workers through their representatives, where appropriate. This information should be used in support of pre-job and post-job evaluations, work planning, control of contamination and management of radiological control operations. Significant changes in monitoring results should be identified and trends should be analysed periodically. Corrective actions should be taken as necessary. Data should be recorded that:
Demonstrate compliance with regulations;
Identify significant changes to the working environment;
Give details of radiation surveys, for example date, time, location, dose rate, airborne activity concentration, instruments used, surveyor or other comments;
Give details of any reports received about the workplace, whereby compliance with relevant requirements could be adversely affected;
Give details of any appropriate actions taken.
3.115.
Particular attention should be given in the selection and use of instruments to ensure that their performance characteristics are appropriate for the specific workplace monitoring situation. Guidance on considerations relating to the acquisition, use, maintenance and testing of workplace monitoring instruments is given in Section 7.
Assessment of exposure
3.116.
Specific requirements for the assessment of occupational exposure are set out in paras 3.99–3.102 of GSR Part 3 [2], which state that:
“3.99. Employers, as well as self-employed persons, and registrants and licensees shall be responsible for making arrangements for assessment of the occupational exposure of workers, on the basis of individual monitoring where appropriate, and shall ensure that arrangements are made with authorized or approved dosimetry service providers that operate under a quality management system.
“3.100. For any worker who usually works in a controlled area, or who occasionally works in a controlled area and may receive a significant dose from occupational exposure, individual monitoring shall be undertaken where appropriate, adequate and feasible. In cases where individual monitoring of the worker is inappropriate, inadequate or not feasible, the occupational exposure shall be assessed on the basis of the results of workplace monitoring and information on the locations and durations of exposure of the worker33.
“3.101. For any worker who regularly works in a supervised area or who enters a controlled area only occasionally, the occupational exposure shall be assessed on the basis of the results of workplace monitoring or individual monitoring, as appropriate.
“3.102. Employers shall ensure that workers who could be subject to exposure due to contamination are identified, including workers who use respiratory protective equipment. Employers shall arrange for appropriate monitoring to the extent necessary to demonstrate the effectiveness of the measures for protection and safety and to assess intakes of radionuclides and the committed effective doses.
“33 The distinction between types of worker in paras 3.100 and 3.101 for the purposes of monitoring has similarities to the distinction between category A and category B workers in European Union legislation [(see Ref. [21])].”
3.117.
An assessment of the exposure of individual workers in normal and foreseeable abnormal conditions should be considered if, for any single component of the exposure (e.g. strongly penetrating photon irradiation, neutron irradiation or internal exposure), the corresponding annual effective dose is expected to exceed 1 mSv. Consideration should also be given to the likelihood and possible magnitude of potential exposures.
3.118.
In general, when the magnitude or variability of the exposure is likely to be significant, an individual worker’s radiation exposure should be assessed from the results of individual monitoring. There are occasions, particularly in the assessment of internal exposure, when this may not be feasible or practicable and reliance should be placed on workplace monitoring. Where this is the case, the monitoring programme should provide detailed information on the worker’s movements and on the temporal and spatial variations in air concentrations in the worker’s immediate environment. Where possible, site specific data on characterization of the workplace should be used rather than default values.
3.119.
For work involving risk of internal exposure, a level of activity concentration in air or intake of activity into the body may need to be established to be used as an indication of whether there is the potential for a significant individual exposure. In the derivation of such a level, the particular radioactive materials and exposure pathways of the relevant workplace should be taken into account to the extent possible. If the level is exceeded, additional direct measurements of the individual’s internal exposure may be necessary. This may also be desirable if there is any doubt as to whether the assessed exposure for the specific workplace conditions is sufficiently accurate.
3.120.
For any assessment of occupational exposure, the accuracy of the particular monitoring procedures or devices used to determine external and internal exposure should be evaluated. The objective should be to establish as comprehensive a record as is reasonable of credible, formally assessed exposures. Account should be taken of the factors affecting the accuracy of the assessment. The accuracy criteria for measurements and their interpretation should be defined, and reasonable and appropriate measures to quantify and minimize uncertainties should be taken.
3.121.
More detailed guidance on assessment of exposure is provided in Section 7.
Investigation levels
3.122.
Experience with a particular situation sometimes indicates a need to review procedures and performance. This experience can be qualitative (e.g. the observation that the frequency of occurrence of minor contamination may have increased) or quantitative (e.g. a trend in the results of monitoring programmes). The use of quantitative experience can be helped by the application of investigation levels to the monitoring results for individuals and workplaces. An investigation level is defined as the “value of a quantity such as effective dose, intake or contamination per unit area or volume at or above which an investigation would be conducted” [2].
3.123.
Investigation levels play an important role in monitoring programmes as tools for use by the management. Investigation levels should be defined at the planning stage of activities and may be revised on the basis of operational experience. The regulatory body may also wish to establish, for regulatory purposes, a generic investigation level in terms of individual exposure. Investigation levels can be set in terms of virtually any measurable quantity relating to the individual or the working environment. They should be defined by the management in the radiation protection programme, their purpose being to facilitate the control of operations and exposures.
3.124.
Investigation levels should be used in a retrospective sense only and should not be confused with dose constraints. If an investigation level is exceeded, a review should be initiated to determine the causes, and to consider the arrangements for protection and safety, and the reasons for the value being exceeded. Such a review may lead to the introduction of additional measures for protection and safety. The review should have the objectives of learning lessons that may be appropriate for any future operations and determining whether additional measures are necessary to improve the current arrangements for protection and safety.
3.125.
Investigation levels should be set by the management on the basis of a knowledge of the conditions in the workplace, the expected levels and variability of the quantities being determined (e.g. effective dose and intake), and the type and frequency of monitoring. The value of the investigation level should also be consistent with the objectives of the monitoring programme and with the type of investigation that will be initiated. The value of an investigation level may be based on a selected fraction of the relevant dose limit, and it should correspond to the period of time to which the individual monitoring result refers. For instance, an investigation level for a routine operation with routine monitoring may be set on the basis of a committed effective dose of 5 mSv from intakes over the course of a year. For N monitoring periods per year, the investigation level ILj (in becquerels) for the intake of radionuclide j in a given monitoring period would be given by:
where e(g)j is the dose coefficient for inhalation or ingestion of radionuclide j, as appropriate (in sieverts per becquerel). The value of the investigation level should be established with other sources of exposure taken into account.
3.126.
A level may be set for individuals involved in a particular operation, or may be derived specifically for individuals within a place of work without reference to a particular operation. The latter situation is particularly relevant when individuals are exposed to a number of different sources in a workplace or are involved in a number of different tasks at work.
3.127.
The management should identify those persons responsible for initiating investigations when they are required. The purpose of, and the actions associated with, each investigation level should be clearly defined in advance. The investigation should address:
The circumstances leading to the suspected exposure;
Verification of the dosimetric results;
The probability that dose limits or levels will be exceeded under current working conditions;
Corrective actions to be taken.
3.128.
Workplace monitoring may involve the measurement of dose rates, contamination levels, airborne activity concentrations or a combination thereof. Investigation levels for workplace monitoring should be set by the management on the basis of the expected levels and operational experience. A value of surface contamination (activity per unit area) derived from a fraction of the relevant dose limit may be useful in indicating the significance of particular measurements, and could, therefore, be used as an investigation level to indicate a deterioration in the radiological conditions in the workplace.
Recording levels
3.129.
During the routine monitoring of the workplace or of individuals, a large amount of data will be generated that may have little quantitative significance in terms of converting them into effective (or equivalent) dose. A recording level is a level of dose, exposure or intake specified by the regulatory body at, or above, which values of dose to, exposure of, or intake by workers are to be entered into their individual exposure records (see para. 3.105(b) of GSR Part 3 [2]). For instance, the recording level for an intake of a radionuclide could be set to correspond to a committed effective dose of 1 mSv from intakes over the course of a year. Thus, for N monitoring periods per year, the recording level RLj (in becquerels) for intake of radionuclide j in a given monitoring period would be given by:
In cases of exposure of workers to radiation of more than one type or to multiple radionuclides, the contributions of each type of radiation or each radionuclide should be taken into account in selecting the recording level for each contribution to the dose, exposure or intake. In the case of individual monitoring for external exposure, the minimum level of detection is usually used as the recording level.
3.130.
For the assessment of internal dose, if the dose or intake is below the recording level, the measurement result should always be maintained in the dose record for the workplace and/or the individual.
Derived investigation and recording levels
3.131.
It may be convenient to express investigation levels and recording levels in terms of the quantities actually measured (i.e. radionuclide activities measured in the body or in excretion samples). These are termed derived investigation levels (DILs) and derived recording levels (DRLs), respectively. They are the measurement values that correspond to the investigation levels or recording levels for parameters such as committed effective dose or radionuclide intake. For intakes of radionuclides, DILs and DRLs are calculated separately for each radionuclide, are specific to the physical and chemical form of the radionuclide in the workplace, and are a function of the period of time between the time of intake and the time of measurement. For the examples given in Eqs (19) and (20):
where m(t0)j is the fraction of the intake of radionuclide j remaining in the body or in the excretion sample after an elapsed time period t0. The value of t0 is usually based on the assumption that the intake occurs at the midpoint of the monitoring period, in which case:
Records of occupational exposure
3.132.
Record keeping is an essential part of the individual monitoring process, as indicated in paras 3.103 and 3.106 of GSR Part 3 [2], which state that:
“3.103. Employers, registrants and licensees shall maintain records of occupational exposure34 for every worker for whom assessment of occupational exposure is required in paras 3.99–3.102. …….
“3.106. Employers, registrants and licensees:
Shall provide workers with access to records of their own occupational exposure;
Shall provide the supervisor of the programme for workers’ health surveillance, the regulatory body and the relevant employer with access to workers’ records of occupational exposure;
Shall facilitate the provision of copies of workers’ exposure records to new employers when workers change employment;
Shall make arrangements for the retention of exposure records for former workers by the employer, registrant or licensee, as appropriate;
Shall, in complying with (a)–(d) above, give due care and attention to maintaining the confidentiality of records.
“34 Records of occupational exposure are also referred to as ‘exposure records’ or ‘dose records’.”
3.133.
The management should establish a procedure that indicates how monitoring data and results are to be reported, which dose levels are to be recorded, and which documents and records of occupational exposure are to be maintained. In general, the dosimetry service provider has limited direct contact with workers and the facility management. Monitoring results are, however, often used by the management to advise personnel with responsibilities for operational radiation protection as to when intervention with workers, such as follow-up sampling or restriction of work, is necessary. Consequently, close cooperation is necessary between those involved in different parts of the monitoring programmes and the protection programmes.
3.134.
Records of individual occupational exposure should include any assessed equivalent doses or intakes, including the dose to the skin and to the lens of the eye, as appropriate. Details of any involvement in abnormal events should be included, even if no estimates of exposure could be made. Records referencing the objectives, monitoring methods and models used for data analysis and interpretation should be retained, because these may be needed for future interpretation of the records of occupational exposure. Traceability of the measurements and of assessments of exposure is essential.
3.135.
The monitoring programme should specify the periods over which monitoring and assessment of exposure are carried out, these being related to the dosimeter processing or sampling programme. Records of occupational exposure for individual workers such that the exposures assessed for these periods are separately identifiable should be constructed.
3.136.
Records of occupational exposure should be kept up to date, and procedures should be established to ensure that assessments of exposure from any monitoring period are incorporated promptly into the individual’s exposure record.
3.137.
Recording systems need to be capable of producing information on the assessment of occupational exposure for any reporting period defined in the radiation protection programme or required by the regulatory body. If a worker changes employment, records of occupational exposure should be promptly updated and completed.
3.138.
The dose records should be easily retrievable and should be protected against loss. Such protection is usually obtained by maintaining duplicate sets of records in well separated locations, so that both copies cannot be destroyed in a single incident. Records should be consolidated for each monitored individual; should be complete and accurate; should be identified by site, purpose, date and originator; and should be legible and intelligible to a qualified person. Consideration should be given to any applicable national requirements or international agreements concerning the privacy of individual data records.
3.139.
If employers, registrants and licensees cease to conduct activities in which workers are subject to occupational exposure, they should make arrangements for the retention of workers’ records of occupational exposure by the regulatory body or by a State registry, or by a relevant employer, registrant or licensee, as appropriate.
3.140.
More detailed guidance on records of occupational exposure is given in Section 7.