Trends in Occupational Exposure in Malaysia Noriah Mod Ali Secondary Standard Dosimetry Laboratory (SSDL) Malaysian Institute for Nuclear Technology Research (MINT) Bangi, 43000 KAJANG, Selangor Darul Ehsan MALAYSIA e-mail: noriaha@mint.gov.my ; Fax:6-03-89250575 Abstract The official occupational radiation monitoring for individuals in Malaysia is managed by the Secondary Standard Dosimetry Laboratory of Malaysian Institute for Nuclear Technology Research (SSDL- MINT). SSDL-MINT is expanding into a new frontier in ensuring good quality personal dosimetry services for around 11,000 radiation workers from 1500 different workplaces throughout the country. The radiation workers could be grouped into 3 categories of job activities, namely medical, industrial and non-destructive testing (NDT). Among the monitored workers, 47% are employed in the industrial sector, 45% in the medical sector and 8% in the NDT sector. Collection, analysis and discussion on radiation dose statistics is one way in which the authority promotes the as low as reasonably achievable (ALARA) concept. This information is an important tool to identify priority areas for dose reduction and to assess efforts undertaken to maintain ALARA doses. The records on distribution doses achieved through radiation protection control are periodically reviewed. These include various types of dose distributions in different occupational categories from 1992 to 2002. It is interesting to note that the percentage of exposed worker exceeding 50 msv was less than 1% and this was maintained for over a 10-year period. This paper shows the desirable characteristics of the distributions of doses based on proper planning, preparation, implementation and review of jobs while applying good job management procedures, so as to achieve ALARA doses. It demonstrates great efforts of the regulating body, Atomic Energy Licensing Board (AELB) and MINT, to inculcate radiation safety awareness among radiation workers through a good radiation protection program at the workplace. It also assures the employers that radiation exposure at their workplace is as low as reasonably achievable. This trend can be maintained and enhanced with further improvement on safety at the workplace. 1. Introduction Whilst a large fraction of radiation work uses well established technology, there is an ever increasing challenges to the optimization of the occupational exposure control. Implementation of the Atomic Energy Act, Act 304, 1984 is acknowledged to be the first step in the harmonization of the Malaysian National Radiation Protection System. The Act is based on the ICRP recommendation and International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources. Legal requirements for individual occupational monitoring are summarized in Basic Safety Standards for protection of the health of workers and the general public against dangers arising from ionizing radiation [1,2]. It involves measuring of radiation by using equipment conducted on the body of a personnel and interpreting of such measurements. It, therefore, involves systematic measurements, evaluations and recording of all exposures to an individual. Individual occupational monitoring as a means for collecting data pertinent to exposures received by an individual in the course of his/her work is managed by the Secondary Standard Dosimetry Laboratory of Malaysian Institute for Nuclear Technology Research, SSDL-MINT [3]. The services began in 1985, where SSDL-MINT has been entrusted to issue personal monitoring devices for assessing dose resulting from occupational exposure to ionizing radiation. Official personal dose measurements from external exposures are mandatory and currently performed on 11,000 workers employed in 1500 institutions, including hospitals, clinics, industries, research and teaching institute. Approximately 47% of the total workers are from the industrial, 45% from medical and 8% from non-destructive testing (NDT) sectors (Figure 1). The medical sector is the oldest user of radiation in Malaysia. Medical use of radiation can generally be split into diagnostic radiology, 1
radiotherapy, nuclear medicine and radiopharmaceutical. The exposed medical workers include radiologists, radiographers, clinicians, technicians and research workers. NDT, 8% INDUSTRIAL, 47% MEDICAL, 45% FIG.1. Distribution of radiation workers in different occupational activities Thermoluminescence dosimetry (TLD) and film dosimetry systems currently constitute the bulk of dosimetry services worldwide (Figure 2). These dosimeters are worn on plastic cases (termed holders) attached to the wearer s clothing and are designed to detect ionizing radiation coming from outside of the body and are calibrated to assess the dose received by the wearer from such sources. The monitoring of worker is carried out on monthly basis and dosimeter readings will be served to ensure compliance with legal dose limits. The routine and systematic collection of data on individual and collective occupational doses categorized by work activity is a key tool to provide information on conditions in the workplace. Safety assessment to practices and sources are conducted (by the Atomic Energy Licensing Board, AELB) on the various facilities in institutions to ensure compliance with the legal requirements and safety of sources and personnel. FIG.2. Types of personal dosimeters issued by SSDL-MINT 2
A national dose registry is created at SSDL-MINT. The registry contains dose information on all monitored workers in Malaysia. The individual dose measurement data from the various working places can be centrally pooled. Therefore, whenever a monitored person changes work sites, the individually documented dose histories can still be computed as one lifetime dose history. This conforms to the objective of radiation protection program laid through Act 304, 1984, to ensure the safe use of atomic energy in Malaysia. Investigations are conducted on cases where personal doses have exceeded an investigation level of 10 msv permonth or when accumulative doses approach or exceed the limit of 50 msv peryear. Advice and recommendations are made to the respective operating institution and staff on the principles of dose reduction and good work practices to avoid further occurrences. Apart from monitoring tasks, the registered data can eventually be prepared for scientific research on radiation protection. 2.Distribution of Occupational Exposure Table 1 provides the summary of the annual accumulative occupational doses on workers from 1992 to 2002. Exposure of workers to ionizing radiation are generally well controlled as it is noted that 90% of the occupationally exposed workers received doses less than 1 msv. About 98% received doses less than 20 msv and 99% received doses of less than 50 msv. Percentage of exposed worker exceeding 50 msv is less than 1%, and this is maintained over a 10-years period even with an increasing number of workers monitored. Table 1. Annual Accumulative Occupational Dose from 1992 to 2002 Year Number of Distribution of workers(%) over dose interval monitored <0.2mSv 0.2 2 msv 20.1-50mSv >50mSv worker 1992 2543 2042(80.3%) 439(17.3%) 42(1.6%) 20(0.8%) 1994 3151 2423(76.9%) 709(22.5%) 16(0.5%) 3(0.1%) 1996 4816 3670(76.2%) 1112(23.1%) 24(0.5%) 10(0.2%) 1998 7039 5117(72.7%) 1809(25.7%) 92(1.3%) 21(0.3%) 2000 9252 7808(84.4%) 1390(15.0%) 44(0.4%) 10(0.1%) 2001 9724 8384(86.2%) 1297(13.3%) 39(0.4%) 4(0.04%) 2002 10696 9118(85.2%) 1554(14.5%) 20(0.2%) 4(0.1%) Table 2 illustrates the detailed patterns in Malaysia occupational exposures from 1999 to 2002. The occupational doses are expressed in terms of both collective and average doses, which give information on the number of people exposed. The collective dose reflects both the dose and the number of people, and is defined as the total amount of radiation exposure to everyone affected by the activity. The average dose is the average radiation dose affected by the activities. The pattern shows a significant decrease in the average annual individual doses with increasing number of workers from 1999 to 2002. The average individual dose is very low, at 0.62 msv per year, and it should be noted that a large number of doses are lower than the recorded levels. Regulatory pressures, technological advances and a global approach to work consistent with ALARA contributed to this decreasing trend. The reduction of dose received is evidence of the implementation of good radiation protection programme at the workplace. 3
Table 2. Distribution of Accumulative Dose, 1999 to 2002 Accumulative dose 1999 2000 2001 2002 (msv) 0-0.1 6824 7717 8133 8898 0.1-0.2 126 90 251 220 0.2-0.4 126 210 240 411 0.6-1.0 176 274 161 220 1.1-2.0 186 268 270 271 2.1-5.0 264 353 330 329 5.1-10.0 165 197 185 186 10.1-15.0 93 55 75 91 15.1-20.0 69 33 36 34 20.1-25.0 37 24 22 18 25.1-30.0 15 7 7 6 30.1-35.0 3 5 5 4 35.1-40.0 6 7 4 4 40.1-45.0 3 - - - 45.1-50.0 4 1 1 - > 50 10 10 4 4 No.of user 7843 9252 9742 10696 Collective dose (man-sv) 7795.2 6839.5 6495.6 6612 Average dose (msv) 0.99 0.74 0.66 0.62 Table 3 provides a detailed breakdown of exposure in the area of occupational groups. Largest component of the collective dose from occupational exposure is from the NDT sector. There are certain areas in the NDT sector whereby very high exposures (higher than 50 msv) are received. Ensuring sufficient attention is paid to control and reduce such exposures requires continues efforts in the training and awareness on the radiation involved. Appropriate training of the workers at all levels is a fundamental building block in the attainment of a good radiation protection safety culture. Updating of training and refresher courses are also known to contribute to a good radiation safety culture. The present scenario in Malaysia on the new recommendations on occupational exposure indicates that the adoption of this limit into current Malaysian Regulation would not be a problem for the radiation workers, where it was shown that only a small number of workers are exposed to radiation exceeding the new dose limit (20 msv). This trend can be maintained and improved with further enhancement in the safety culture at the workplace. A key challenge is to improve safety culture characteristics, which relate to the widening of the scope of disciplines and specialists using radiation beyond those that have had radiation protection as an element in the professional training. This is being addressed through improvements to the formal training programs. Improvements in source design and engineering could also reduce the frequency of high dose events. Similar comments are also relevant to the use of gauge sources in general industry, and the wider issue of source security is becoming a significant international concern with lost sources becoming a hazard to worker groups who are not normally exposed to radiation. 4
Table 3. Distribution of Occupational Doses Among Occupational Category, 2002 Accumulative dose Occupational Category (msv) Medical Industrial NDT 0-0.1 3920 4896 94 0.1-0.2 40 30 170 0.2-0.4 179 45 27 0.4-0.6 98 39 23 0.6-1.0 133 39 48 1.1-2.0 123 59 89 2.1-5.0 132 63 134 5.1-6.0 22 19 104 6.1-10.0 17 4 46 10.1-20.0 8 32 71 20.1-50.0 5 5 - > 50 - - 4 No.of user 4677 5211 808 Collective dose (man-sv) 2093 1812.8 3168.6 Average dose (msv) 0.45 0.35 3.92 3. Summary The historical lower in annual dose of radiation worker in Malaysia is clearly affected with the evolution in the aspects of the controlling of occupational exposure. This indicates great effort by the regulating body, AELB and MINT to inculcate radiation safety awareness among the workers by providing a good radiation protection program at the workplace. New challenges also represent an opportunity to improve the way work is done, and the radiation protection system should lead to greater maturity as the system is conducted with enhanced quality. This will result in a better working situation and confidence in the radiation protection community. References (1) LAW OF MALAYSIA, ACT 304: Atomic Energy Licensing Act 1984. (2) INTERNATIONAL ATOMIC ENERGY AGENCY, International Basic Safety Standards For Protection against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series No.115, IAEA, Vienna (1996) (3) N. Mod Ali, T. Kadni, R. Mohd Shariff, Harmonizing of Occupational Radiation Monitoring Malaysia, IAEA-CN-91/2, International Conference On Occupational Radiation Protection: Protecting Workers Against Exposure To Ionizing Radiation, Geneva, Switzerland (2002). (4) Noriah Mod Ali & Taiman Kadni, Harmonizing of Radiation Protection in Workplace, presented at Radiation Protection Officer (RPO) Conference, Langkawi, Malaysia, September 2000. 5
(5) Noriah, M.A. Implementation of A Quality System Based on ISO 9001 Requirement in Malaysia National Dosimetry Services For Monitoring External Radiation Exposure, presented at International Conference on National Infrastructures For Radiation Safety: Towards Effective and Sustainable Systems, Morocco, 1-5 September 2003. 6