IRR17 (9) - Restriction of exposure

Notwithstanding the importance of risk assessment (IRR17 - Regulation 8), this regulation is just as significant. It presents a large part of the current philosophy of radiation protection - as prescribed by ICRP. Under the ICRP principles, you should investigate alternative methods of getting the job done that use non-ionising radiation techniques (although by the time you arrive at this site it is assumed that ionising radiation use is justified).

Every radiation employer must take all necessary steps to restrict, so far as is reasonably practicable (ALARP), the extent to which their employees and others are exposed.

Two important issues in this regulation are as follows

  • Dose sharing should not be the primary means of keeping exposures below dose limits.
  • For employees not normally exposed to ionising radiation during the work, the employer must take specific steps to ensure its unlikely that any such person would receive an effective dose exceeding 1mSv (or any other limit for “other persons” as specified in Schedule 3 of IRR17).

Where appropriate ALARP measures should be engineered into the work with ionising radiation, this takes away the 'thinking element' (i.e. consideration of time, distance, shielding, practical handling techniques and similar). This is possible for certain work using external radiation sources (e.g. fully shielded and interlocked radiation enclosures used for industrial radiography or cancer treatment radiotherapy treatment rooms). Where internal radiation hazards exist, for example unsealed radioactive materials used in medical diagnostic imaging, more emphasis is placed on 'doing the right thing' (so ALARP needs much more real time on the job consideration).

Generally, Ionactive clients are encouraged to try and maintain a dose constraint of no more than 1mSv effective whole body dose for any employee. This then guarantees the second statement above for all, regardless if they are actually 'working' with ionising radiation.

IRR17 Regulations 9 sets out a hierarchy of control measures – these being similar to that used in all modern UK health and safety legislation.

These need to be applied during the design, construction, installation, and use of sources of ionising radiation:

  • Engineering controls
  • Warning devices
  • Systems of work, training, local rules and instructions
  • Personal protective equipment

In the case of a female employee who has advised her employer that she is pregnant, occupational exposure must be reduced so that the dose to the foetus is unlikely to exceed 1mSv during the remainder of the pregnancy. This is covered automatically if the employer implements a local dose constraint of 1mSv for all employees (male or female). The ease in which an employer can implement this dose constraint for all routine work and reasonably foreseeable accidents will depend on the nature of the work. This is far easier to achieve for external radiation sources, and may be impossible to guarantee for certain work with unsealed radioactive materials (in which case withdrawal from radiation work may be the only reasonably practicable option).

In relation to a female employee who has advised her employer that she is breastfeeding, the employer must take steps to ensure the avoidance of significant bodily contamination. This is of course only relevant to those who work with unsealed forms of radioactive material.

For the purpose of determining whether doses are as low as reasonably achievable (ALARP), an employer must carry out an investigation of the doses received by any employee having accrued a dose of 15mSv, or more, in any calendar year. In practice, a much lower limit than this will be specified in the local rules. Given that Ionactive encourages most clients to maintain less than 1mSv whole body dose per year, then investigation levels in many cases are set at levels where dosimetry records 'something' above background. Such investigations are of course proportional to the low level of risk from such low exposures.

There is a lot of detail in IRR17 Regulation 9, much of which will only be relevant to certain types of ionising radiation use. You are therefore encouraged to download a copy of the IRR17 ACoP from HSE and have a good read through this particular regulation.

The definition of 'safe' is not strictly an engineering term; it's a societal term. Does it mean absolutely no loss of life? Does it mean absolutely no contamination with radiation? What exactly does 'safe' mean?

– Henry Petroski -