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Further details on meeting the requirements of : "Work with ionising radiation" Ionising Radiations Regulations 1999: Approved Code of Practice (ACOP) and guidance.


Hierarchy of control measures

Safety related interlock control systems for X-ray sets

74 Regulation 8(2) establishes a hierarchy of control measures for restricting exposure. First and foremost, in any work with ionising radiation, radiation employers should take action to control the doses received by their employees and other people by engineered means.

Lasermet has many years of experience in safety control engineering

75 Usually, radiation employers will achieve the most effective restriction of exposure by taking control measures at an early stage, for example when the facility or device is being planned and designed.

Lasermet's expertise is in developing failsafe safety control systems which are ideally planned in at the facility design stage

Types of physical control measures

76 Engineering controls and design features are normally those physical controls built into the facility or device; they include all aspects of the design and construction which restrict exposure.

77 Safety features are intended both to help ensure the safe use of the equipment in normal operation and to prevent unintended exposure in the event of a failure of control devices or systems of work. Examples include locks on exposure controls, search and lock-up systems, door interlocks for enclosures and emergency exposure controls ('off' buttons).

Lasermet's safety control systems, which are failsafe, permit equipment to be operated only when all of the relevant safety interlocks are in the safe mode. Emergency buttons are also included as part of the interlock control system.

78 Warning devices indicate the status of the equipment in normal operation and alert operators to faults or failures which have occurred and which reduce the safety integrity of the installation.

Warning devices which include Lasermet's LED signs and audible warning system indicate the status of the equipment. The ICS-6 dual channel, interlock control system has indicators on the front panel which shows if a fault is present preventing the system from arming.

ACOP Exposure controls

87 Where control systems permit, interlocks or trapped key systems should be provided and properly used where they can prevent access to high dose rate enclosures (for example in which employed persons could receive an effective dose greater than 20 millisieverts or an equivalent dose in excess of a dose limit within several minutes when radiation emission is under way).

They should be fitted so that the control system will ensure an exposure:

(a) cannot commence while the access door, access hatch, cover or appropriate barrier to the enclosure is open;

(b) is interrupted if the access door, access hatch, cover or barrier is opened; and

(c) does not recommence on the mere act of closing a door, access hatch, cover or barrier.

The Lasermet interlock controller is keyswitch enabled.

(a) Dual channel switches and maglocks are fitted to doors, hatches and windows. The circuit feeds back to the interlock controller which prevents equipment operation unless all of the contacts are closed and /or magnetically locked.

(b) If any of the doors or interlock switches are opened while the equipment is being operated, the equipment is disabled within 50ms.

(c) To re-enable the system, the interlock must be manually reset.

92 The ACOP advice in paragraph 87 means that effective interlock devices should normally be designed and installed in such a manner that if they fail to operate correctly no exposure of people can occur. Although it should be reasonably practicable to install these devices where enclosures or cabinets are provided around X-ray generators, it may sometimes be more difficult to provide them for sealed source equipment because of the method of controlling the source. However, the installation of such devices with this type of equipment is often reasonably practicable.

Lasermet's interlock controller is a start-to-end, cross-checked, dual channel control system designed to operate (with the relevant wiring systems) at ISO 13849-1 Performance Level 'e'. (Safety of machinery: Safety-related parts of control systems). This is the highest performance level. (A complete list of compliance with all of the relevant directives and standards is provided in the ICS-6 specifications).

Key-operated safety devices

96 Where there is a risk of significant exposure arising from unauthorised or malicious operation of X-ray generators or radioactive source containers, radiation employers should make use of equipment which has been fitted with locking-off arrangements to prevent its uncontrolled use.

97 The initiation of exposures should be under key control, or by some equally effective means, so as to prevent unintended or accidental emission of a radiation beam or exposure of a source. This is particularly important where the control point is remote from the equipment which will be activated or there is general access to equipment by members of the public or personnel who are not undertaking the work with ionising radiation.

The ICS-6 must be switched on with a key.

Warning devices

99 Sources of ionising radiation which can give rise to significant exposure in a very short time should be fitted with suitable warning devices which:

(a) indicate for a radioactive source whether it is in or out of its shielding (or the exposure shutter is open or closed);

(b) indicate for an X-ray generator when the tube is in a state of readiness to emit radiation and, except for diagnostic radiology, give a signal when the useful beam is about to be emitted and a distinguishable signal when the emission is under way unless this is impracticable;

(c) for X-ray generators other than those used for diagnostic radiology, are designed to be automatic and fail-safe, ie if the warning device itself fails the exposure will not proceed.

100 The radiation employer should make sure that warning signals can be seen or heard by all those people who need to know the status of the radiation equipment for protection purposes.

Lasermet manufactures a range of low voltage, dual colour, dual message LED signs and audible warning devices that connect to the interlock control system. The controller can also be monitored remotely (e.g via ethernet network).

101 Automatic warning devices should be reasonably practicable for most X-ray generators and some sealed sources. Therefore, radiation employers using large sealed sources will need to consider how signals could be provided. In particular, automatic generation of the pre-exposure and exposure warning signals is possible where there is a fully automated mechanism for the exposure and retraction of the source. If it is not reasonably practicable to follow the ACOP advice in sub-paragraph 99(c) that warning devices should normally be fail-safe, daily checks that such devices are working might suffice in the short term, at least. Where a visual device relies on a single bulb, it may be sufficient to modify the device to use two bulbs.

Lasermet manufacture and supply both mains and low voltage LED illuminated signs. Mains types feature two low energy lamps.
Low voltage types use LED's for long life and high reliability. 'Ultra' signs can be ordered with dual redundant illuminators, lamp fail signalling and auto dimming function.

102 In some cases, warning signals will need to be seen or heard by people who may be outside the immediate area. Therefore, the radiation employer might provide explanatory notices for people not directly involved in the work, pointing out any action they should take in response to a warning signal. These notices will be of little use if they fail to explain clearly the significance of the different signals and the action to be taken. The radiation employer might need to consult the appointed safety representative(s) for the area about such notices.

Lasermet's LED signs and audible warning devices can be added to remote locations away from the immediate area.

Manual warning signals, radiation monitors and warning

103 Where equipment containing a radioactive source is not fitted with automatic warning signals, it may be appropriate for the operator to make use of a manual system to generate clear and distinguishable pre-exposure and exposure warning signals. Signals are particularly important when people in or around the designated area need to be aware of the status of the source. Notices and signs can explain the significance of these signals and the action to be taken.

107 Where appropriate, any signs used to indicate high dose rate areas should conform to the Health and Safety (Safety Signs and Signals) Regulations 1996.13
Where the area concerned has been designated as a controlled area or a supervised area, the requirements of regulation 18 may also be relevant.

Regulation 10

Maintenance and examination of engineering controls etc and personal protective equipment

(1) A radiation employer who provides any engineering control, design feature, safety feature or warning device to meet the requirements of regulation 8(2)(a) shall ensure

(a) that any such control, feature or device is properly maintained; and

(b) where appropriate, that thorough examinations and tests of such controls, features or devices are carried out at suitable intervals.

165 All active engineering controls and design features (eg local exhaust ventilation systems), safety features (eg electromechanical interlocks) and warning devices should be subjected to a regime of examination and test at suitable intervals.

General advice on maintenance of controls

166 'Maintained' is defined under regulation 2 in relation to plant, apparatus, equipment and facilities. 'Maintenance' means 'maintained in an efficient state, in efficient working order and good repair'.

167 The objective of this regulation is to ensure that all physical control measures such as shielding, enclosure, ventilation, safety features and warning devices provided in accordance with regulation 8(2), perform as originally intended. It may not be reasonably practicable to ensure at all times that complex enclosures or safety devices are in an efficient state and in efficient working order.

173 The ACOP at paragraph 165 advises that, in addition to the visual checks already mentioned, active control measures such as exhaust ventilation systems, electromechanical interlocks and warning devices will usually need to be examined and tested at suitable intervals. Typically, a suitable interval might be about once a year, depending on the circumstances of the work.

Consultation on procedures for maintenance

174 Regulation 13 and Schedule 5 require a radiation employer to consult a suitable RPA on the periodic examination and testing of engineering controls etc appropriate to the equipment they use (see paragraphs 226-227). RPA advice should help the employer to develop a programme of examination and test for appropriate control measures. The appointed safety representative(s) or established safety committee might also be consulted. The employer should also consider the recommendations of the manufacturer or supplier on the programme for the inspection and test of the different control measures.

Ordering information and quotations

To obtain a quote and to specify your order please contact the sales department at Lasermet on 01202-770740 or email requesting a Required Information form. This is to specify the system required. Once this is completed we can provide a quotation.

If you would like to discuss the interlock system or have any related questions, we would be pleased to discuss this with you.