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Section E

Dose restriction

 

Regulation 8 of IRR’99 requires the Employer to take all necessary steps to restrict as far as is reasonably practicable the extent to which persons are exposed to ionising radiation.
In order to achieve this several control measures may be utilised:

  • physical control measures (room design, Pb screens)
  • systems of work (do not enter room when red light is on)
  • monitoring radiation levels (environmental monitoring)
  • use of PPE (only necessary if monitoring estimates indicate that PPE is required)

i)   Dose Limits
Regulation 11 (1) requires the Employer to ensure that persons are not exposed to ionising radiation where relevant dose limits would be exceeded. Schedule 4 (part 1) of the regulations detail the various classes of people within a radiation environment together with their respective dose limitations.
See Schedule 4 of IRR’99 to note the effective dose limits for all class of persons to whom dose limitations apply.

  • Employees (classified – 20mSv/year)
  • Employees (non-classified – 6mSv/year)
  • trainees under 18 years of age (6mSv/year)
  • trainees under 16 years of age (1mSv/year)
  • comforters & carers (5mSv/year)
  • members of the public (1mSv/year)
  • pregnant Employees (not to exceed 1mSv for the remaining term of pregnancy (i.e. the remaining time following notification to the RPS/RPA)
  • certain organs – skin – 500mSv/year (1cm square of skin)

For further information on dose limitations to the lens of the eye, the skin and other body areas see pages 48 – 50 and 140 – 141 of L121 (HSE, 2000)

ii)  Designation of work areas

Regulation 16 of IRR’99 details the requirements for the Employer to designate work areas, where ionising radiation is used, into controlled or supervised areas. Designated areas require adequate demarcation (Regulation 18), systems of work for all non-classified staff, and a monitoring system of a person’s dose exposure.

Controlled area – where doses may be significant (>6mSv/year or three-tenths of any relevant dose limit) and where special procedures are carried out. Inside the treatment units in a radiotherapy department are designated as “controlled areas” with the control panel area generally not being designated as such. The treatment room is only “controlled” when the power is on – the warning lights go out when the power is off. Many RPAs also advise that x-ray rooms are controlled areas thus requiring the use of radiation warning signs and lights.

Supervised area - where doses are > 1mSv/year or an equivalent dose > one-tenth of any dose limit in Schedule 4 (usually control panels etc)
 

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