Designation of Controlled Areas

Should the radiation risk assessment determine that:

• It is necessary for a person entering an area to follow special procedures in order to restrict significant exposures or
• While working in the area they could receive an annual radiation dose exceeding the threshold values given in regulation 17(1)(b) of IRR17

then a controlled area (CA) needs to be designated.

For dental radiography, the risk assessment should confirm that the potential for staff to incur doses in excess of the threshold values is minimal. However, staff will be required to follow special procedures to restrict significant exposure and as such it will be necessary to designate a CA. The purpose of designating CAs is to control who can enter or work in such areas and under what conditions.

Extent and Demarcation of the Controlled Area

The extent of a CA must be determined in consultation with the practice’s RPA. The regulations say that, where reasonably practicable, a CA must be physically demarcated in order to restrict unauthorised access. The Dental GNs recommend designating the whole room containing the X-ray equipment as a CA (shown shaded in blue below). The room boundaries clearly demarcate the area and this assists with the restriction of access. The Dental GNs also recommend that this designation is always used for rooms containing dental CBCT equipment.

Where it is not reasonably practicable to designate the whole room, a smaller CA may be designated. The Dental GNs recommend that in this case, the CA should be designated within 1.5 m of the X-ray tube head and patient, and for intra-oral radiography within the primary beam until suitably attenuated (shown shaded in blue below). This choice of CA has the disadvantage that the CA boundary is not physically demarcated and restriction of access relies solely on the operator maintaining continuous supervision.

Duration of the Controlled Area

The CA should be designated whenever the X-ray equipment is in a state of readiness to emit X-rays. For most equipment, this is defined as the point at which power is supplied to the equipment. However, for equipment where access to the exposure controls can be restricted entirely through use of computer passwords (most CBCT and newer panoramic/cephalometric units), this is defined as the point at which the operator has logged on and set up a patient on the software.

At the end of the radiography session, the power supply to the X-ray set should be switched off or the operating computer locked. The radiation hazard no longer exists so the area is no longer a CA and access does not need to be restricted.

Restriction of Access and Other Requirements

Controlled area warning signs must be displayed at all points of access to the CA. Signs should consist of a radiation trefoil and the wording ‘X-rays controlled area – no unauthorised entry’ and should be placed on the door(s) prior to switching the X-ray set on/entering the password. If the CA has multiple doors, it may be possible to restrict access by other means such as locking the doors or positioning another member of staff outside the door. These arrangements would need to be documented in the local rules.

Once the equipment has been switched off or the operating computer locked and the controlled area no longer exists, the warning signs must be removed/covered.

If warning lights are used, then where possible they should be connected so that they illuminate automatically whenever the equipment is in a state of readiness. However, this may not be practicable/possible if the equipment cannot be switched off between uses or if hand-held equipment is being used. Any warning lights must be suitably labelled or accompanied by a suitable warning notice to explain the meaning of the light and the action to be taken.

If it is not reasonably practicable to physically demarcate a controlled area, it may not be practicable to provide warning signs. If so, one or more staff members must be present to give an appropriate verbal warning to anyone approaching the boundary of the controlled area.

Working in the Controlled Area

Staff will need to enter the CA, either to set up the patient/X-ray equipment, remove the image receptor or because they are using hand-held equipment. Staff may only enter the CA in accordance with suitable written arrangements, which should be set out in the local rules (see step 4.5 in week 4 of this course). The written arrangements are, in effect, the ‘special procedures’ to restrict exposure. IRR17 requires the employer to demonstrate that they are effective, either by issuing personal dosemeters or by means of other suitable measurements (see week 4, step 4.4).