Radiological incidents where there is the potential for the release of ionising radiation can occur in a wide variety of scenarios - be it a fire in an industrial facility, a transportation accident that involves radioactive materials or the deliberate use of a radiological dispersal device (RDD).
Any accident or incident that involves a radiological hazard can place significant operational demands on first response teams as well as placing those personnel at risk of exposure to potentially dangerous levels of ionising radiation.
Radiation exposure refers to any situation in which the body is in the presence of radiation.
In order to keep radiation doses at a level that is low as reasonably achievable (ALARA) it is vital that first responders both minimise the time that they spend in affected areas and that they maximise the distance between themselves and the radiation source.
When we consider the concept of radiation exposure it is important to bear in mind not just the type of radiation that is being emitted, but also the route by which that radiation enters the body.
A commonly held image of radiation is that it emanates from a source device and strikes the outside of the body - in what's known as external exposure.
However the radioactive material from radiation also has the ability to deposit its energy in our internal organs through the process of ingestion, injection, absorption or inhalation - what is termed internal exposure.
What is external radiation exposure?
External radiation exposure occurs when part or all the body is exposed to a penetrating radiation field from an external source. In some cases this radiation will be absorbed by the body, while in others it may pass straight through.
Any source outside of the body that emits ionising radiation can pose an external radiation exposure hazard - be it in the form of a beta source, neutron source or gamma source.
How extensive this hazard is depends on the amount of exposure received, the duration of the exposure, the energy of the emitted radiation and the total amount of radioactive material that is present.
All ionising radiation sources produce an external radiation field, however some radiation fields are so so small that they pose no radiation risk at all - for example in the case of low and moderate energy beta radiation emitters such as Tritium (H-3), Nickel-63 (Ni-63) or Phosphorus 33 (P-33).
Other sources of ionising radiation - such as the gamma sources Caesium-137 (Cs-137) and Cobalt-60 (Co-60) - are able to produce much more powerful external radiation fields, so care must be taken to shield the source and monitor exposure.
What is internal radiation exposure?
Internal radiation exposure occurs when a radioactive material is released into the environment in the form of a solid, liquid or gas.
It is then able to enter the body through the route of ingestion through the digestive tract, inhalation into the respiratory airways, percutaneous absorption through the skin or penetration via contamination from a wound.
Radioactive materials that are incorporated into the body will emit radiation as they decay. In addition, that individual will continue to be exposed to radiation until such time as those radioactive materials have been excreted in the form of either urine or faeces.
Specific radioactive materials have a tendency to target specific organs depending on their unique chemical properties.
The radioactive isotope strontium, for example, shares similar properties with calcium, which means it tends to accumulate in calcium-rich areas of the body such as bones.
Radioactive caesium shares properties that are similar to potassium, which means it tends to distribute throughout the body.
Radio-iodine, meanwhile, tends to concentrate in the thyroid gland in the same manner as non-radioactive iodine (and the effects of which were evidenced after the Chernobyl nuclear accident where there was a marked increase in the number of thyroid cancer cases among children.)
Any exposure to ionising radiation in the context of a radiological emergency - and even if it is only for short periods of time - can increase the chance of both short-term and long-term health impacts for first responders.
In any situation where there is deemed to be a radiation hazard it will be crucial to ensure that emergency personnel are sufficiently trained in managing the risks, that they are adequately equipped and that they are appropriately protected.