The maximum permissible contamination levels specified in The Ionising Radiations( Unsealed Radioactive Substances) Regulations 1968 were adopted by the nuclear industry as acceptable levels for the clearance of items out of Controlled Contamination Areas and were also adopted by the Road Transport Regulations.
In 1977 the use of MPBB was deemed unacceptable because an accidental exposure could bar someone from ever working in a controlled area again. It was replaced by a system based on the Annual Limit of Intake, from which Derived Air Concentrations are derived.
The NRPB published guidance on designation and classification of areas. As further evidence on risk became available, ICRP recommended a reduction in annual dose limits for classified workers from 50 mSv to 20 mSv in 1991. These were adopted by the majority of countries, with the exception of the USA. A revised set of dose coefficients was published in supplements to ICRP 60 and reissued in ICRP 119.
To support the new recommendations, the IRRs were revised in 1999. These required employers to use a more risk-based approach for the designation of areas, and detailed guidance was given in the accompanying Approved Code of Practice. However, in practice the original contamination levels are still in widespread use for clearance from contaminated areas, as they are near the limit of detection and they are still in use under the IAEA Transport Regulations.
Radiation Signage
Hazard and warning signs must conform to the requirements of The Health and Safety( Safety Signs and Signals) Regulations 1996, and subsequent amendments, which implemented the requirements of EC Directive 92 / 58 / EEC. The Health and Safety Executive( HSE) has issued accompanying guidance document L64 currently in its third edition.
Signs fall into four categories: prohibition, warning, mandatory and emergency escape / first aid. The guidance gives full details on the shape and colour of the sign.
Warning signs for radiation comprise a yellow triangle, with a yellow text box below with further information, such as classification of the area.
A Controlled Radiation Area sign with text box
Ionising Radiation Non Ionising – lasers
CONTROLLED AREA
Ultraviolet Non Ionising
Radiation Protection Supervisor......................................................... Telephone:.....................................
18 Radiation Protection Today www. srp-rpt. uk