ALARA is an acronym for “As Low As Reasonably Achievable”. It is a fundamental radiation safety principle for minimizing radiation exposure and releases of radioactive material, while taking into consideration economic and social factors. Not only is it a sound safety principle, it is a regulatory requirement for all radiation safety programs. At the University of Ottawa over 20 year period, the Radiation Safety Program has been based on the ALARA principle. Inventory control has kept the quantity and activity of radioisotopes to a minimum, users are knowledgeable, procedures are followed and no individual has ever received a dose close to the regulatory limit.
An effective ALARA based radiation safety program is only possible when a commitment to safety is made by all those involved and the principal should be used in all laboratory operations. Holistically as the Radiation safety Program, ALARA is ensured by the issuing of Internal Permits, training and authorizing users, approval of radioisotope purchases, assessing use and disposition records, contamination monitoring and radiation surveys, reviewing dosimetry exposure records, and decommissioning of permits, rooms and equipment.
In the laboratory, the ALARA principle can be followed by:
1) Designing the experiment/procedure so the lowest possible amount of radioactive material is used and length of time in the radiation field is minimized.
2) Wearing dosimeters, if applicable, when working with radioactivity. (TLD are unable to detect radiation exposure to H-3, C-14, S-35 or Ca-45)
3) Providing bioassay samples when required. (Unbound I-125 or I-131 can accumulate in the thyroid Individuals, at a single time, using more than 135 µCi (5 MBq) of I-125 or I-129 on the open bench or more than 1.35 mCi (50 MBq) in a fumehood must participate in a thyroid monitoring program.)
4) Reporting incidents or unsafe practices to their supervisors and, if appropriate, the Radiation Specialist
5) Being aware of potential radiation hazards, exposure levels and safety controls in the laboratory
6) Knowing the operating and emergency procedures
Mitigation Of External Radiation Exposure
There are three principles that can be used to limit to exposure to radiation:
1) Time – minimizing the time or exposure directly reduces the radiation dose.
2) Distance – doubling the distance between your body and the radiation source will divide the radiation exposure by a factor of 4.
3) Shielding – using an absorber such as Plexiglas for beta particles and lead for X-rays and gamma rays is an effective way to reduce radiation exposures
Mitigation Of Internal Radiation Exposure
The following practices are effective for reducing potential internal exposures:
1) Good hygiene techniques that prohibit the consumption of food and drink in the laboratory, and the control of personal gestures that involve “hand-to-mouth” contacts.
2) Frequent wipe tests and radiation surveys of work areas, refrigerators, hoods, sinks, phones and computer keyboards. etc.
3) Control contamination with absorbent paper and spill trays, properly labelled waste containers, equipment, etc. and prompt decontamination of any detected contamination.
4) Use fume hoods for materials which could become airborne (e.g., vapours, dust, aerosols, etc.) and present an inhalation hazard to workers.
5)Use proper protective equipment such a disposable glove, safety glasses, lab coats, etc.
Doses are recorded on thermoluminescent (TDL) dosimeters provided by Health Canada Dosimetry Program. The dosimeter wearing period is 3 months. At the end of 3 months, they are returned to Health Canada for dose analysis (reading). Exposure reports are generated and sent by Health Canada before the next wearing period. If an individual receives a dose, they will be contacted by the Radiation Specialist. If an atypical dose (usually 0.6 -0.8 mSv) is received, it will be investigated to determine the cause.
Dose limits are set by the Canadian Nuclear Safety Commission (CNSC), Radiation Protection Regulations.
Maximum permissible annual dose to the whole body for the general public* is 1 mSv , for Nuclear Energy worker (NEW) it is 50 mSv Maximum permissible annual dose to extremities (hands, feet) for the general public* is 50 mSv , for Nuclear Energy worker (NEW) it is 500 mSv *Under CNSC criteria, employees at uOttawa are classified as members of the general public.
Radiation surveys are generally performed by the Radiation Specialist during a Full laboratory inspection. If atypical radiation fields (usually 5 times above background) are measured, an investigation will be done.
CNSC defines an action level as "a specific dose of radiation or other parameter that, if reached, may indicate a loss of control of part of a licensee's radiation protection program, and triggers a requirement for a specific action to be taken."
At the University of Ottawa, action levels are atypical doses or atypical radiation fields.
A uOttawa's action levels are:
- A dose of 0.3 mSv over a 3 month dosimetry wearing period. Note, if this dose was to continue, the individual could exceed the University of Ottawa's (public exposure limit) of 1 mSv in a year.
- Atypical radiation fields (usually 5 times above background).
If an action level is reached, it will trigger an investigation to determine why the action level was reached, and then determine the action required to remediate the situation so that the action level is not reached in the future. With atypical radiation fields, there may be associated doses to individuals and these will be assessed.
Preventative measures to avoid action levels being reached is achieved by following the ALARA principle, adhering to procedures, being knowledgeable (trained) and planning for unusual situations.
Keeping Radiation Exposures and Doses "As Low as Reasonably Achievable (ALARA) CNSC Regulatory Guide G0129
Developing and Using Action Levels, CNSC Regulatory Guide G-228