Stainless steel barriers, lead aprons, air filtration systems, respirators...the wide array of devices designed to keep employees who work with radiation sources on a daily basis “out of harm’s way” reflect a key principle in occupational exposure control. The radiation protection measure must be adequate to the source.
While this topic might bring to mind nuclear power plant employees clad in “spacesuits”, the majority of radiation workers apply their skills in other industries and come in close contact with many different types of ionizing radiation. Like their cohorts in nuclear energy, radiologists and radiology technicians, industrial radiographers, research scientists, food processors, manufacturers, etc., typically work with man-made sources of radiation or radiation-producing machines (e.g., X-ray generators used in diagnostic radiology or industrial irradiators used for sterilization). In contrast, for individuals who work in mines, mills and raw material processing plants, the exposure risk is associated with naturally occurring radionuclides (atoms that are radioactive) such as uranium and thorium, and their decay products (e.g., radon and radium).
Distinctions in the setting and the source determine, to a large degree, whether workers are more likely to face risks associated with “internal” or “external” exposure – depending on whether a source is sealed (e.g., encapsulated in stainless steel for use in gamma radiography) or unsealed (e.g., used in a liquid format as in nuclear medicine). The vast majority of occupational exposure is associated with routine operations; dose levels are carefully controlled and as long as procedures are followed carefully, little risk is encountered. But if an accident occurs — a sealed source breaks open or an unsealed source is dispersed — high levels of radiation can affect specific organs or the whole body.
Clearly, exposure control in occupational settings is a multi-faceted challenge — and employers hold all of the responsibility for protecting worker health and safety. Some degree of exposure is a given; thus, regulations in this area relate to controlling dose levels (how much radiation an individual receives) and obtaining accurate exposure measurements. The regulatory authority carries out a dual role in this regard. On one hand, it must oversee regulations related to dose limits and implementing a systematic approach to optimizing radiation protection. On the other, it must ensure that monitoring and measurement services are available and capable of delivering reliable results. The regulatory authority plays a vital role in protecting workers through its power to carry out inspections and to suspend or revoke the licenses of facilities that fail to maintain standards set out by the Basic Safety Standards.
Recognizing that radiation protection in the work environment involves a wide range of rights and obligations for both employers and employees, the IAEA partnered with the International Labour Organization (ILO) to develop standards in this area. Together, these bodies identified three main areas of concern: individual monitoring and workplace monitoring; health surveillance and occupational exposure records; and general radiation protection information and training for workers. Effective monitoring comprises three elements: a) the individual — monitoring the amount of ionizing radiation to which the employee is exposed; b) the equipment — performing regular tests to ensure that equipment is functioning properly; and c) the environment — ensuring that the indoor and outdoor environments (i.e., buildings, surfaces, earth, soil and water) have not become dangerously contaminated over time.
For the most part, external radiation exposure monitoring is carried out through the use of thermoluminescent dosimeters (TLDs), small packets containing radiosensitive material, and electronic personal dosimeters that employees wear while on the job. Employers are required to replace these on a regular basis and to send the used TLDs to an independent licensed laboratory for analysis. Depending on the type of radioactive contaminant, internal exposure is usually calculated using monitors that detect doses of inhaled radioactive gas (such as radon) or radioactive particles suspended in the air, through urine/excreta analysis or through whole body counting, in which a large detector directly measures gamma rays being emitted by employees and others in the workplace. Employers must also keep accurate, up-to-date records on each employee’s exposure dosage to ensure that the cumulative effect does not exceed the dose limits.
The IAEA has been helping Member States develop workplace monitoring, as well as in individual dose monitoring and analysis. In many cases, the IAEA has delivered either TLDs or the TLD readers necessary for analysis. On a regional basis, there has been a concerted effort to introduce yet another level of assurance through the establishment of secondary standard dosimetry laboratories (SSDLs) for calibration of radiation detection devices.
Individual monitoring is critical to employee protection. But if dosimetry results are not credible, they are essentially useless. Since the early 1980s, the IAEA has been organizing regional and international “intercomparisons” of radiation detection devices for external and internal dosimetry. For example, an SSDL will prepare identical sets of TLDs that have been irradiated with different doses of various radiation sources. Each monitoring facility must read the TLDs and report their findings. If their readings are incorrect, it is apparent that their system (equipment, calibration and procedures) is not giving accurate measurements. Another aim of the project—called Intercomparison of Radiological Measurements for Monitoring Purposes— is to harmonize the use of radiological quantities and techniques.
Some Member States use different units of measurement for radiation; it is recognized that the conversion processes required to make comparisons introduces an unnecessary error factor. Harmonization will further improve the regulatory authority’s ability to contribute to the development of international standards, the service provider’s ability to accurately assess doses, and the employer’s ability to properly protect the health and safety of employees.
According to estimates by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), more than 80% of annual collective dose to workers worldwide derives from occupational exposure in workplaces that have elevated levels of natural radiation (much higher than in workplaces where man-made radiation is regulated). This fact is not fully considered in existing guidelines and is thus an area requiring further development.