Australian Clinical Guidelines for Radiological Emergencies - September 2012

Radiation Protection

Page last updated: 07 December 2012

Introduction

Radiation protection standards recognize that it is not possible to eliminate all radiation exposure, but they do provide for a system of control to avoid unnecessary exposure and to keep doses as low as reasonably achievable. Measures for control of exposure for stochastic (latent, probabilistic) effects seek to minimise all reasonably avoidable risk. This is called optimising protection. However, risk in this sense may often be assessed in terms of risk to a population, and may not ensure sufficient protection of the individual. Consequently, the optimisation approach is underpinned by applying dose limits that restrict the risk to individuals to an acceptable level.

The fundamental regulatory philosophy is expressed in three principles, based on the recommendations of the International Commission on Radiological Protection (ICRP), which may be summarised as follows:
  • Justification: human activities that cause exposure to radiation may be permitted only if they do more good than harm;
  • Optimisation of protection: exposure to radiation from justified activities should be kept as low as reasonably achievable, social and economic factors being taken into account; and
  • Limitation of individual dose: doses must not exceed the prescribed dose limits.
The Australian radiation protection framework in ARPANSA Radiation Protection Series 1, Recommendations for limiting exposure to ionising radiation (2002) is consistent with that recommended by the ICRP and endorsed by the International Atomic Energy Agency, the World Health Organization, and the International Labour Organisation. The recommended dose limits are summarised as follows:

Table 2.1 Recommendations for limiting exposure to ionising radiation
ApplicationDose Limits OccupationalDose Limits Public
Effective dose20 mSv per year, averaged over a period of 5 consecutive calendar years
    1 mSv in a year
    Annual equivalent dose in the lens of the eye
150 mSv
    15 mSv
    Annual equivalent dose in the skin
500 mSv
    50 mSv
    Annual equivalent dose in the hands and feet
500 mSv

Reference: Recommendations for limiting exposure to ionizing radiation (1995) and national standard for limiting occupational exposure toReference: Recommendations for limiting exposure to ionizing radiation (1995) and national standard for limiting occupational exposure to ionizing radiation (republished 2002); Radiation Protection Series No. 1; ARPANSA.

In most situations, the requirements for limiting individual risk ensure that doses are below deterministic thresholds.

In an emergency, where there may be a need for emergency personnel to take action to save lives or to bring an accident under control, these radiation dose limits may no longer be appropriate. In emergency situations where compliance with the dose limits is not possible, every effort should be made to keep the doses to emergency personnel below those specified in the Table below (from Intervention in Emergency Situations Involving Radiation Exposure, ARPANSA Radiation Protection Series Publication No. 7, (2004)). Radiation doses to response personnel for all actions, including life-saving action, must be kept well below those at which serious deterministic health effects may occur.

Table 2.2 Total effective dose guidance for emergency situations
TasksTotal effective dose guidance [mSv]
Type 1:
Life-saving actions
<500
Type 2:
Prevent serious injury
Avert a large collection dose
Prevent the development of catastrophic conditions
<100
Type 3:
Short term recovery operations
Implement urgent protective actions
Monitoring and sampling
<50
Type 4:
Longer term recovery operations
Work not directly connected with an accident
<20

Reference: Recommendations for intervention in emergency situations involving radiation exposure (2004); Radiation Protection Series No. 7; ARPANSA.

Personnel undertaking a Type 1 task must be fully aware of radiation hazards and the consequences of radiation exposure. The benefits to others must clearly outweigh the risks to the emergency personnel. The individual should be trained in radiation protection and they must be instructed on the potential consequences of exposure. They should be in good health and be well trained for the necessary emergency task. They must wear personal monitors that provide estimates of personal radiation dose. Breathing protection, protection of the skin against beta radiation and contamination and other protective devices must be provided and used when necessary. All personnel will need to be closely monitored by a Radiation Safety Officer (RSO) to ensure that exposure to external radiation does not exceed the relevant radiation dose limits specified above.

Radiation Measurement

Radiation cannot be detected by the human senses. A radiological survey conducted with specialized equipment is the only way to confirm the presence of radiation. In the response to a radiation emergency there are three types of radiation monitors; survey meters, contamination monitors and personal dosimeters.

Typically, gamma radiation is detected with radiation survey meters that are calibrated to read out in units of effective dose rate. Survey meters for use at low levels of radiation have Geiger-Müller detectors or a scintillation detector such as sodium-iodide (NaI) for increased sensitivity. High levels can be measured with a high range Geiger-Müller detector or an ionization chamber. Survey meters are available to measure from lethal dose rates of Sv/h down to background radiation levels below a few microsievert per hour.

Most beta emitters can be detected with a survey instrument (provided the metal probe cover is open). Some beta emitters, however, produce very low energy, poorly penetrating radiation that may be difficult or impossible to detect. Examples of these are carbon-14, tritium, and sulfur-35.

Contamination monitors use a radiation detector with a thin window pancake probe for increased sensitivity to alpha and beta radiation. Thin window Geiger-Müller probes will detect alpha, beta and gamma radiation. Scintillation probes can be selected for detection of alpha or beta radiation. Contamination monitors are calibrated to display in units of count rate or activity (Bq). Contamination probes need to be positioned close to the radiation source, but they cannot detect alpha radiation through even a thin layer of water, blood, dust, paper, or other material, because alpha radiation is not penetrating. Special training in use of these instruments is essential for making accurate measurements.

Pocket chamber (pencil) dosimeters, film badges, thermoluminescent, and other types of electronic integrating dosimeters can be used to measure accumulated exposure to gamma radiation.

Airborne particulate radiation is a potential respiratory hazard. It is measured using a pump which draws the contaminated air across a filter for a fixed period of time. The amount of radioactivity deposited on the filter can be measured using the appropriate survey or contamination meter.

Minimising Radiation Effects

The cornerstones of personal safety are:
  • radiation hazards decrease with distance from the source, in inverse proportion to the square of the distance
  • minimising time in the vicinity of the source
  • using shielding where available
  • aviodance of internal contamination by appropriate use of protective equipment and personal hygeine
  • source intensity
  • strict adherence to instructions given by the radiation safety officer (RSO).
    In the event of a radiation emergency and other emergencies involving radiation exposure, the initial safe distances in the Table below should be used in minimising the dose to emergency personnel. The actual boundaries of the safety and security perimeters should be defined in the way that they are easily recognizable (e.g. roads) and secured. However, the safety perimeter should be established at least as far from the source as indicated in the Table below, until the situation has been assessed.

    Table 2.3 Initial safe distances in radiological emergencies
    Initial determination - Outside
    Situation Initial inner cordoned area
    (Safety perimeter)
    Unshielded or damaged potentially dangerous source30 m around or at readings of 100 mSv/h
    Major spill from a potentially dangerous source100 m around or at readings of 100 mSv/h
    Fire, explosion or fumes involving a potentially dangerous source300 m radius or at readings of 100 mSv/h
    Suspected bomb (potential RDD) exploded or unexploded400 m radius or more to protect against an explosion
    Initial determination - Inside a building
    Situation Initial inner cordoned area
    (Safety perimeter)
    Damage, loss of shielding or spill involving a potentially dangerous sourceAffected and adjacent areas, floors above and below
    Fires or other event involving a potentially dangerous source that can spread materials throughout the building (e.g. through the ventilation system)Entire building and appropriate outside distance indicated above
    Expansion based on radiological monitoring
    Situation Initial inner cordoned area
    (Safety perimeter)
    Dose rate of 100 mSv/hWherever these levels are measured

    Reference: Recommendations for intervention in emergency situations involving radiation exposure (2004); Radiation Protection Series No. 7; ARPANSA.