7. Laboratory designation
Contents
7.1.4 Designation Where There Are Both Internal And External Hazards
7.2 Suitability of Laboratories
7.3.1 Access to Service Personnel
7 Laboratory Designation
7.1 Designation of Areas
All areas where ionising radiation sources are located must be identified and described in the School/Unit local rules. These areas must be designated as either a 'Controlled area', 'Supervised area' or a 'General Laboratory area' (see below). All such designations must be approved by the URPA.
There are three types of radiation area defined in the Ionising Radiations Regulations 1999. These are:
- Controlled Area
- Supervised Area
- Non-designated Area (General Laboratory Area)
The definitions of these areas are given in Appendix 19.
Working at the University, you are unlikely to receive any significant dose of radiation in any laboratory, providing you follow the information and instructions that you are given. However, we are not allowed to designate all our laboratories as non-designated because the likelihood of receiving a dose of radiation is defined by a number of factors which are laid down in the Ionising Radiations Regulations. Bearing this fact in mind, we need to consider four distinct types of work when determining the grade of laboratory:-
- Work where there is only an external hazard.
- Work with X-ray equipment.
- Work where there is only an internal hazard.
- Work where there is both an internal and external hazard.
7.1.1 External Hazard only
A controlled area is required where the instantaneous dose is greater than 7.5 µSvh-l to the whole body for more than 16 hours a week and greater than 75 µSvh-l to the hands.
A supervised area is required where the instantaneous dose rate exceeds 2.5 µSvh-l to the whole body and 25 µSvh-l to the hands.
A general laboratory area can be used where the instantaneous dose rates do not exceed 2.5 µSvh-l to the body or 25 µSvh-l to the hands and exposure times are limited to less than 8 hours a week at this exposure rate.
The above is a slight simplification, as one is allowed to use further time-averaging to allow higher dose rates than those stated for a supervised area. If this flexibility is required, then the Radiation Protection Adviser should be consulted.
7.1.2 X-ray Laboratories
A controlled area is required for X-ray work, when beam paths are not enclosed, or where the enclosure does not prevent access to areas where the dose rate exceeds the limits specified in para 7.1.1.
A supervised area is required when all beam paths are normally enclosed, but where some overriding of interlocks is required for alignment procedures, or where only the X-ray camera itself is providing the local enclosure.
A general laboratory area classification can be used when a totally enclosed system is employed with no override provision on interlocks, such that it is not normally possible to gain access to dose rates in excess of 2.5 µSvh-1.
7.1.3 Internal Hazard Only
One has to consider the need for a controlled or supervised area on the basis of a risk assessment.
The National Radiological Protection Board (NRPB) analysed operational scenarios and exposure pathways to calculate the maximum quantity of different isotopes that could be handled in different categories of laboratories. The University has considered this analysis when setting specific limits for the storage and use of unsealed sources. These limits are given in Appendix 20 which is titled - 'Maximum Permitted Activity of Unsealed Radionuclides which may be Stored/Used at One Time'.
If more than one isotope is used, then the amount that can be used/stored is calculated using the Quantity Ratio. This is determined using the calculation:
Qp
(Sum) ------
Qlim
Qp = Quantity of radionuclide present
Qlim = Quantity of the radionuclide specified in Appendix 20
NOTE: The quantity ratio must NOT exceed 1
Using the most restrictive ALIs for inhalation or ingestion the above quantities equate to the following activities for the common radionuclides used in universities.
Table X - ALIs/Activities for the Common Radionuclides
| Radionuclide | 1 ALI | 30 ALI | 120 ALI |
| H-3 (water) | 1.1 GBq | 33 GBq | 132 GBq |
| H-3 (OBT) | 470 MBq | 14 GBq | 56 GBq |
| C-14 | 34 MBq | 1 GBq | 4 GBq |
| S-35 |
15 MBq |
450 MBq |
1.8 GBq |
| P-32 |
6.2 MBq |
186 MBq |
744 MBq |
| P-33 |
14 MBq |
420 MBq |
1.7 GBq |
| I-125 |
1.3 MBq |
39 MBq |
156 MBq |
| Cr-51 |
530 MBq |
16 GBq |
64 GBq |
7.1.4 Designation where there are both internal and external hazards
Where radionuclides present both an internal and an external hazard then a realistic assessment should be made of the likely doses that will result from the proposed work and every effort must be made to reduce these by the use of appropriate shielding. Working to an internal dose constraint of 0.2mSv, it will be the control of the external hazard, and whether special procedures are required to ensure this, that will determine the need, or otherwise, for a controlled area.
7.2 Suitability of Laboratories
Permission will only be granted for work with ionising radiations if a suitable laboratory is available. This is particularly important for work with unsealed sources, for which special surface finishes may be required to the walls, floors and bench tops, and special facilities may be required for hand-washing, waste disposal and to guard against air contamination. Further information on the design requirements of laboratories for unsealed sources is available from the Radiation Protection Service.
7.3 Access to Laboratories
Only those laboratories specified on the project application or 'System of Work' may be used for radioactive work up to the levels permitted therein. The entrance to all areas specified must bear the appropriate warning notice and, if required, a notice limiting access. Access to radiation areas is restricted as follows:-
(a) controlled areas - classified radiation workers and other registered radiation workers following a written system of work. An example of a 'Scheme of Work' is given in Appendix 21.
(b) supervised areas - registered radiation workers and other persons whose presence, work or duties can be so controlled that they will not be exposed to significant amounts of radiation. The latter must be advised as to how they may fulfil this requirement.
(c) general laboratory areas no restriction on the grounds of radiation hazard.
7.3.1. Access to Service Personnel
School/Unit staff must give special consideration to service personnel, who are unfamiliar with ionising radiation and the hazards involved.
When access is required to a controlled area by non-classified personnel who are not covered by a written system of work, then that area should be de-designated by the DRPS or another person who has the authority of the Head of School/Unit, prior to entry being permitted.
Any person de-designating a laboratory should ensure that: the area has been monitored and found to be free from contamination; all sources of ionising radiations are either in store or shut down (X-rays and neutron generators); and nowhere in the area does the instantaneous dose-rate exceed 7.5µSvh-1. They should then put an appropriate notice on the entrance to the laboratory.
Before cleaning staff are allowed to start their duties, they must be told which areas have been monitored and cleared, and not to clean any other area. It may well be convenient for the cleaning staff to deal with the floor areas, and designated laboratory staff, bench tops and other surfaces. If this is the case, the cleaner must be instructed accordingly. Adequate instruction must be given over the segregation of radioactive and non-radioactive waste and the cleaner instructed not to deal with waste in the former category. If cleaning of glassware or other contaminated apparatus is necessary, steps must be taken to ensure there is no contamination hazard to the cleaning staff.
Each situation clearly presents its own particular problems and these cannot be dealt with adequately here. The DRPS should formulate plans, guided by the above, and seek the advice of the University Safety Adviser on any matters which are not clear.
7.4 Signage
The appropriate sign for identifying material or areas that may contain radioactive materials is the trefoil. An example of this is shown here:
Appendices 22 and 23 show the University of St. Andrews signs that identify areas designated as 'Controlled Areas' and 'Supervised Areas' respectively. The sign to show where radioactive substances are being used in a 'General Laboratory Area' is given in Appendix 24. Areas where radioactive materials are being stored are identified using the sign given in Appendix 25. Sinks which are designated for the disposal of aqueous water miscible radioactive waste is given in Appendix 26.