Regulatory Compliance – Prior Risk Assessment

The prior risk assessment (Regulation 7) is a key feature of IRR99 and should be completed by a radiation employer for all activities involving ionising radiation.

Put simply a risk assessment is a careful examination of what in the course of your work could cause harm to people. IRR99 states: ‘before a radiation employer commences a new activity involving work with ionising radiation, he shall make a suitable and sufficient assessment of the risk to any employee and other person for the purpose of identifying the measures he needs to take to restrict the exposure of that employee or other person to ionising radiation’. The Prior Risk assessment (PRA) must identify all hazards with the potential to cause a radiation accident and then the nature and magnitude of the risks to employees arising from those hazards must be evaluated.

Some definitions are useful when talking about risk assessments:

  • Hazard – the potential to cause harm
  • Risk – the likelihood of the hazard being realised

The PRA should enable the employer to produce procedures detailing the action necessary to reduce exposure to ionising radiations to as low a level as reasonably practicable (ALARP).  It is standard practice to draw up these procedures in the form of protocols, working instructions and local rules.

For the risk assessment to be suitable and sufficient, the following matters should be given careful consideration (where relevant):

  • Nature and magnitude of sources of ionising radiation to be used, or likely to be present (including the accumulation of radon).
  • Estimated radiation dose rates to which anyone could be exposed as a result of the process
  • The likelihood of contamination arising and being spread.
  • Estimated levels of airborne and surface contamination.
  • The nature of the work to be carried out.
  • The results of any previous personal dosimetry or area monitoring relevant to the proposed work.
  • Control of access to the working area.
  • The control measures already in place.
  • Availability and effectiveness of personal protective equipment.
  • Accident situations, their likelihood and potential severity (spillages, fire, failure of control measures, such as interlocks, fume cupboards etc).

Useful reference data for calculating potential radiation dose rates, airborne and surface contamination and intakes following exposure include:

  • The Radionuclide and Radiation Protection Data Handbook. 2002. Delacroix et al.
  • Methodology for Estimating the Doses to Members of the Public from the Future Use of Land Previously Contaminated with Radioactivity.  NRPB-W36.  March 2003.  Oatway and Mobbs.
  • Morris, B W; Darby, W P & Jones, G P (1995).  Radiological Consequence Models for Workers on a Nuclear Plant.  AEA/CS/RNUP/47820021/Z/1.  Issue 1.
  • J Austin (1993).  Radiological Wounds – Risk Assessment.  SASWP(93)P27.

Nuvia use the following tables to assign severity factors, frequency factors and risk ratings based on consideration of each reasonably foreseeable radiological accident scenario.

Severity Factor

Description (relevant to radiological hazards)


Limited radiological consequences e.g. minor spread of contamination / negligible dose


Whole Body Effective Dose up to 1 milliSv / Significant spread of contamination


Whole Body Effective Dose between 1 milliSv and 20 milliSv


Effective dose likely to exceed any dose limit


Effective Dose likely to be above tissue effect threshold

Frequency Factor



Extremely Unlikely Occurrence – So unlikely that the probability is close to zero


Unlikely / Possible Occurrence -unlikely though conceivable


Likely / Occasional occurrence – will occur several times


Very Likely / Frequent Occurrence – Not surprised that the harm has occurred


Almost certain / Regular Occurrence – Occurs repeatedly / Event to be expected

Risk Rating (RR)  =  Frequency Factor (FF) x Severity Factor (SF)

Risk Rating (RR)


Action Required


Low (L)

None or limited action


Medium (M)

Additional control measures should be used where reasonably practicable


High (H)

Redesign the task / operation if control measures do not control the risk

Where the risk assessment shows that a radiation accident is reasonably foreseeable then you should have a contingency plan. The contingency plan should secure the restriction of exposure and the health and safety of persons who may be affected by such an accident.