Requirements for the Safe Use of Baggage X-Ray Inspection Systems - Safety Code 29

4. Standards, Surveillance and Monitoring

Within the scope of the ICRP system of radiological protection including the As Low As Reasonably Achievable (ALARA) principle, the collective equivalent dose(1) associated with the use of baggage x-ray inspection systems must be minimized. This use involves a large number of individuals and, therefore, the x-ray inspection systems and human factors must be considered.

4.1 X-ray systems

4.1.1 Regulatory standards

All baggage x-ray inspection systems sold in Canada must conform to the Radiation Emitting Devices (RED) Regulations (Schedule II, Part IV), at the time of sale. These regulations are promulgated under the RED Act, and it is the responsibility of the manufacturer or distributor to ensure that the x-ray system conforms to the regulatory requirements. Since the regulations are subject to amendments in order to reflect changes in technology, information on their current applicability may be obtained by contacting the X-Ray Section, Bureau of Radiation and Medical Devices, Health Protection Branch, National Health and Welfare, Ottawa, K1A 1C1. Any violation of the RED Act is a criminal offence.

When selecting or procuring a baggage x-ray inspection system, the owner (or designated representative) is advised to obtain a copy of the most recent regulations to become familiar with those requirements, and to enquire of the intended manufacturer or importer if the product complies with those current regulations. (These actions may eliminate or minimize the need for modifications to the system. Such modifications may be costly and cause considerable inconvenience because of disruption in service.)

4.1.2 Installation requirements and commissioning tests

Baggage x-ray inspection systems must be used in a manner that will minimize the number of people in close proximity, so as to lower the possibility of external x-ray exposure. The following requirements apply to all facilities:

1. Every baggage x-ray inspection system must be located in such a way that under conditions of use:
   
   
   1. individuals whose baggage (or other belongings) is to be screened with the x-ray inspection system must be more than 0.50 meters away from the access openings of the irradiation chamber while the x-ray beam is on; and
   2. members of the general public, excluding staff authorized to work with or near the systems and those individuals whose baggage (or belongings) is to be screened, must be more than 2 meters away from the x-ray inspection system.
      
      
2. Every baggage x-ray inspection system must be thoroughly tested and verified by trained maintenance personnel, as per section 3.3, to ensure that all radiation shielding components and safety devices, including warning lights are installed and functioning, before the x-ray system is commissioned for use.

4.1.3 In-house surveillance and maintenance

The reliability and safety of any physical system decreases with age and use because of component wear. Consequently, to ensure safe and reliable operation after baggage x-ray inspection systems are installed, the system owner or designee must establish and enforce a suitable maintenance program that accounts for the age and frequency of use of that system.

4.1.3.1 In-house surveillance

Subsequent to the commissioning tests indicated in section 4.1.2(2) and before any baggage x-ray inspection system is used, trained personnel (maintenance worker or senior operator) must undertake the following procedures:

1. test and ensure that all safety devices (interlocks, switches, warning lights, indicators, etc.) are functioning, as intended;
2. examine and ensure that all radiation shields (panels, lead drapes, etc.) are free from structural damage that could compromise barrier protection;
3. verify that the x-ray inspection system is not exposed to snow or rain, that liquid-filled containers are not placed on top of the x-ray system, and that warning signs at the access openings of the irradiation chamber, including the x-ray "ON" lights, are in clear view; and
4. ensure that the requirements to limit public access, as specified in section 4.1.2(1), are satisfied.

4.1.3.2 Maintenance guidelines

It is not possible to provide guidance in this Safety Code for all scenarios that could cause unsafe events. When such events occur, the procedures indicated in paragraphs 3.1.8 and 3.3.6 apply.

1. Moving and/or relocating an x-ray inspection system Moving and/or relocating x-ray systems can affect components critical to safety. If a baggage x-ray inspection system is moved and/ or relocated, maintenance personnel and/or other suitably qualified person(s) (e.g., senior operator(s)) on site, appointed by the system owner or designee, must observe the following procedures:
   
   
   1. test and ensure that all safety interlocks are functioning properly as intended by design;
   2. examine and ensure that all radiation shields are free from structural damage (i.e., puncture, hole, dent, missing part);
   3. examine and ensure that the lead clamps that hold the anode and cathode terminals onto the chassis of the x-ray tube housing assembly are positioned correctly;
   4. conduct the normal in-beam quality imaging-tests and, if discrepancies exist, investigate the x-ray tube assembly, the collimator setting, and the radiation exposure parameters (tube current, high voltage, filters, etc.) for possible causes; and
   5. ensure that all problems are resolved satisfactorily before the x-ray inspection system is used.
      
      Note: Moves of a few centimeters may not warrant all these procedures. If an ionization-chamber survey meter is used for performing in-beam quality imaging-tests, the average meter readings must be compared with those taken before the x-ray inspection system was moved, and differences of more than 10% must be investigated as to root cause. The proper functioning of the survey meter should be checked first, followed by the items indicated in paragraph 4.1.3.2(1)(iv).

2. X-ray tube or its shielded housing Whenever an x-ray tube or its shielded housing is to be replaced,strict adherence to the manufacturer's instructions in the maintenance manual must be followed. In addition, the following procedures must be undertaken:
   

   1. identify and clearly mark 5 or 6 positions (where radiation measurements will be made) at the top and at the sides of the x-ray tube-head assembly cover, before proceeding with the intended replacement task;
   2. make and record radiation measurements (using the "rate mode" option on the ionization-chamber surve y meter provided) at each position while the x-ray system is emitting x-rays in the continuous mode under normal operating conditions;
   3. remove the x-ray tube-head assembly cover and follow the appropriate manufacturer's procedures to complete the intended replacement task;
   4. replace the x-ray tube-head assembly cover, and repeat procedure 4.1.3.2(2)(ii);
   5. compare the average meter (rate) readings obtained in procedures 4.1.3.2(2)(ii) and 4.1.3.2(2 )(iv) and, if differences greater than 10% occur, identify and correct the problem;
   6. examine and ensure that the lead clamps that hold the anode and cathode terminals onto the chassis of the x-ray tube housing assembly are positioned correctly; and
   7. ensure all problems are resolved satisfactorily before the x-ray system is released for use.

Note: If problems arise during the field situations indicated in (1) and (2) above or in other circumstances, maintenance personnel must maintain detailed and complete records, inform the system owner or designee of such problems, and take appropriate corrective actions. If problems persist, contact the appropriate radiation protection regulatory authority. (Facilities under federal jurisdiction may contact the X-Ray Section of the Bureau of Radiation and Medical Devices. Other facilities should contact their provincial regulatory authority as per Appendix.) If there are no problems, the x-ray inspection systems may be returned into operation.

4.1.4 Radiation protection surveys

A radiation protection survey is intended to establish that the x-ray inspection system functions according to applicable performance standards, and that it is used and maintained to provide maximum x-ray safety to all individuals. To achieve this objective, the following requirements apply:

1. Baggage x-ray inspection systems must be surveyed regularly. While the frequency of surveys depends on the conditions of use, performance history and type of x-ray system, the appropriate radiation protection regulatory authority should determine the required survey frequency. (For facilities under federal jurisdiction, inspections may occur once every two to three years.)
2. A radiation protection survey must be requested from the appropriate radiation protection regulatory authority when:
   
   
   1. x-ray systems of uncommon or new designs are installed (permission may be granted in special cases for restricted use after consultation with the regulatory authority);
   2. in-house surveillance tests have failed to identify and correct any radiation emissions that exceed the regulatory limit and/or the operational values needed to establish image quality assurance criteria during normal use or following modifications or maintenance operations; or
   3. a radiation accident has occurred.
      
      
3. Surveys must be performed by the appropriate radiation protection regulatory authority. Authorized equivalents may be permitted provided that prior approval has been obtained from the appropriate regulatory authority.
4. Surveys must include:
   
   
   1. an inspection of all safety devices and radiation shields;
   2. radiation measurements over the entire x-ray inspection system that are carried out under simulated worst-case conditions, to ensure compliance with the regulatory limit (0.5 mR h^-1 (0.13 µC kg^-1 h^-1) at 5.0 cm from any external surface of the x-ray inspection system);
   3. an assessment of occupational and public exposures when stray radiation has exceeded the regulatory limit; and
   4. a safety and performance assessment of the x-ray inspection system between survey periods by reviewing:
      
      
      1. the most recent survey report specific to the system being surveyed, together with any corrective measures recommended and/or instituted on that system or at the facility since the last survey,
      2. maintenance records that identify which components critical to safety were replaced or repaired, and the tests carried out and their results, and
      3. reports of radiation exposure incidents or unsafe events or accidents, including the corrective actions implemented; and
         
         
   5. appropriate audits to ensure compliance with section 3.1 of this Safety Code.
      
      
5. Survey reports must include the following:
   
   
   1. an identification of the baggage x-ray inspection system revealing the system manufacturer, brand name, model number, and year of manufacture;
   2. an assessment of the safety devices, radiation shields and the occupational exposure levels to personnel and the general public; and
   3. specific corrective actions, if any, that are required for compliance with this Safety Code, including the completion date.
      
      
6. After a baggage x-ray inspection system has been decommis-sioned, all reports of surveys, accidents, radiation exposure incidents and x-ray system misuse, must be retained for a period of at least three years by the system owner or designee at the facility at which the x-ray inspection system was last operated.

4.2 Human considerations

4.2.1 Safe operating guidelines

Even though operational baggage x-ray inspection systems may conform to the requirements set out in the RED Regulations (Schedule II, Part IV) and preventive maintenance programs ensure safety and reliability, improper use may lead to unnecessary external x-ray exposures and accidents. To reduce this possibility, the following minimum guidelines apply to all facilities utilizing baggage x-ray inspection systems:

1. No person must commit any acts that cause unsafe events on an x-ray system when it is in operation. Lifting the lead drapes for any reason when the x-ray beam is on, or exposing any part of the body to the x-ray beam, or covering the x-ray ON lights or x-ray warning signs are examples of unsafe events.
   Note: Although an x-ray inspection system may be specifically installed or arranged to prevent lifting the lead drapes as indicated above, or to prevent access to the entrance and exit openings of the irradiation chamber, appropriate safety warnings (written statements coupled with suitable light indicators) must be legible and in clear view at the point where items are initially presented for x-ray screening.
2. No person must create physical or mechanical conditions that ultimately make the x-ray inspection system unsafe to operate. Defeating safety devices, placing liquid-filled containers on an x-ray inspection system, positioning x-ray inspection systems in confined spaces for carrying out routine maintenance and operational test functions, and positioning x-ray inspection systems for use in areas exposed to rain or snow are examples of hazardous conditions.
3. Operators and maintenance personnel must forbid unauthorized individuals from remaining near an x-ray inspection system longer than is warranted.

4.2.2 Personal exposure monitoring

Personal dosimeters are intended to monitor occupational doses, thereby, providing a mechanism for restricting future radiation exposures to an individual so that the recommended maximum permissible limits are not exceeded. The results o f extensive radiation surveys performed by the Bureau of Radiation and Medical Devices have shown that when baggage x-ray systems comply with the RED Regulations (Schedule II, Part IV) and are maintained and operated by competent personnel, there is no detectable radiation exposure above natural background to the operator. In addition, an analysis of stray radiation survey data that spanned an 8-year period (1978-1985) revealed that the estimated exposure at the positions occupied by baggage x-ray system operators were indistinguishable from background radiation levels⁽⁵⁾. There is no evidence of increased cancer risk at natural background levels^{(6 )}. Hence, personal monitors are neither required nor recommended.

In 1990, the ICRP recommended average annual whole-body dose equivalent limits of 20 mSv y^-1 (2 rem y^-1) and 1 mSv y^-1 (100 mrem y^-1) for a radiation worker and a member of the public, respectively (ICRP 1990⁽¹⁾). These limits do not include medical and natural background radiation exposure contributions since they are judged to be beneficial and unavoidable, respectively. The surveys and analysis results mentioned above are not inconsistent with the recently ICRP revised maximum permissible dose equivalent limits for members of the public.