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Exposure to radiation

Hazard Knowledge

Radiation is the general term given to the process by which energy is transmitted away from an energy source. The term can be applied equally to heat, light, microwave, radio or atomic sources of energy. This guidance is only concerned with the radiation arising from atomic sources, as only these along with electrically generated x-rays have the property of causing ionisation when they interact with other substances; they are referred to as ‘ionising radiations’.

Two basic hazards which arise when dealing with radioactive materials:

  • Irradiation, which is generally, but not exclusively, associated with sealed sources; this can cause harm through an external exposure (the source is located outside the body and possibly some distance away).
  • Contamination, which is covered in the Hazard – Radioactive contamination

In all cases of exposure to ionising radiation, the principle of ‘as low as reasonable practicable’ (ALARP) applies. This means that, even though there is a legal maximum permitted absorbed dose, all exposures must be minimised.

The principle of time/distance/shielding should be used to protect against the harmful effects of penetrating radiation.

  • Time – the shorter the duration of the exposure, the smaller the accumulated dose
  • Distance – the greater the distance from the source of radiation, the lower the dose rate (the ‘inverse square’ law applies - doubling the distance reduces the dose rate to one quarter )
  • Shielding – in general, the higher the density and greater the thickness of the shielding, the better the protection.

To manage the dose received when in an area of elevated radiation levels, a survey meter should be used to continuously assess the dose rate being received.

At any site where radionuclides are stored and used, a risk assessment will have been undertaken to determine potential dose rates and working times. A hazardous materials adviser (HMA) can make use of this information at an incident, to ensure the principles of radiation protection are implemented. However, radiation monitoring equipment should always be used as a key risk control measure in radiation protection procedures.