Safety Code 34. Radiation Protection and Safety for Industrial X-Ray Equipment

4. Additional Guidance

This section provides information for guidance purposes.

4.1 Industrial Radiography Accelerators

Accelerators used for industrial radiography produce photons in the MeV range at high dose rates. For example, a 3 MV-Linatron accelerator can produce a dose rate of 3 Gy per minute at 1 metre and a similar device operating at 9 MV can yield a dose rate of 30 Gy per minute at the same distance ⁽¹⁶⁾.

High-energy (MeV) photons can interact with atomic nuclei, causing nuclei transformation and release of energy in the form of photons or energetic particles or a combination of both. One such particle can be a neutron. The interaction process is called photodisintegration. This reaction is energetically feasible whenever the photon energy exceeds the binding energy of a proton or neutron in the atom nucleus. For materials heavier than hydrogen, except beryllium, the photon threshold energy for such reactions is generally >5 MeV ⁽¹⁷⁾ . For accelerators operating at <6 MV, the neutron yield from photodisintegration reactions would be extremely low and therefore would not be a concern as a radiation hazard ⁽¹⁸⁾.

4.2 Industrial Radiography Underwater

This procedure normally employs radioactive-based sources. The procedure, practice or radiation source is beyond the scope of this Safety Code.

4.3 Non- Radiography Uses of Industrial X- ray Equipment

Industrial x-ray equipment may occasionally be used for purposes other than industrial radiography. In a facility in which this is the case, it is the responsibility of the industrial x-ray machine owner in that facility to (a) ensure that individuals using the x-ray equipment for non-radiography purposes have the appropriate education, training and competence; and (b) determine the individuals' suitability for the particular job intended.

Radiation safety education should be consistent with that of a Radiation Safety Course, such as the one administered by the NDE Institute of Canada ⁽¹⁹⁾ or equivalent. The training and education should include:

1. basic atomic and radiation physics;
2. a knowledge of x-ray production and interaction of ionizing radiation with matter;
3. radiation detection and measurement methods, including survey meters;
4. basic understanding of biological effects of ionizing radiation;
5. personnel monitoring devices;
6. fundamentals of radiation protection: time, distance, shielding;
7. ICRP principles and applicable radiation dose limits to workers and the public;
8. applicable regulations and operational standards for the specific industrial x-ray machine;
9. instructions on the operation, radiation hazards and safety specific to the industrial x-ray machine to be used;
10. discussion of the relevant radiation surveys and results specific to the industrial x-ray machine(s); and
11. emergency procedures.

The RSO shall identify the subset of industrial x-ray equipment users who are engaged in non-radiography work, and ensure that they have the necessary education and training and have demonstrated competence before undertaking the job in question. Except for the certification criterion, the requirements of Section 2.3 of this Safety Code shall apply to that subset of industrial x-ray machine users.

4.4 Personnel Monitoring

Personnel monitoring devices are needed to record and control whole-body exposures to ensure occupational limits are not exceeded in accordance with the ICRP recommendations (Appendix II of this Safety Code). For external dose monitoring purposes, devices should be worn on the clothing closest to the body either at the waist or chest level. Patented and state-of-the-art personnel monitoring systems, capable of registering and reporting dose levels as low as 0.01 mSv, are readily available ⁽¹²⁾ ; older technology also exists ⁽¹³⁾. As a general guide to users of ionizing radiation sources, it is extremely important to notify your dosimetry service provider of the radiation sources you are using or likely to use, seek the appropriate passive dosimeters, and ensure that your occupational doses reported, correctly reflect the contribution from the various radiation sources you are using.

Industrial radiographers and other users must wear photon-sensitive passive dosimeters as well as instantaneous reading electronic alarm dosimeters. Each passive personal dosimeter must be worn by only one individual. It is advised that passive detectors be stored in a secure, properly shielded location between periods of use to avoid registering exposures from extraneous sources. Personnel monitoring data need to be retained as a permanent record and be made readily available for review by industrial radiography personnel, other users of the equipment and the regulatory authority.

Computation of occupational doses for purposes of assessment against worker dose limits recommended by the ICRP (refer to Appendix II in this Safety Code) must be based on the summation of all exposures incurred by the individual from the ionizing radiation sources used in industrial radiography. Photon-sensitive passive detectors collectively record x-ray and gamma-ray components. Natural background radiation or medical radiation contributions are not computed as occupational exposures.

An electronic personnel dosimeter not only provides direct dose reading capability, but also is designed to emit an audible signal intended to provide instantaneous feedback to its wearer about the radiation conditions prevailing in an area. The alarm set point may be for a dose rate or an integrated dose. Electronic alarm dosimeters shall (i) be checked to ensure proper functioning before use; (ii) be set to give an alarm at a preset dose equivalent rate of 5 mSv/h or an integrated dose of 2 mSv⁽¹⁴⁾ , with an accuracy of ± 20 %of the true radiation dose; (iii) be calibrated at periods not exceeding 12 months; and (iv) require special means to change the preset alarm function. Following activation of the alarm, the dosimeter wearer is obligated to exercise appropriate radiation control measures to reduce his or her occupational dose. Such dosimeters work reasonably well for conventional x-ray (and gamma-ray) sources. However, there are radiation sources that produce very high x-ray levels in a time frame in the order of microseconds (e.g., flash x-ray sources ⁽²⁰⁾ ) and the electronic personnel dosimeter may not have sufficient time to respond within that time frame; this sub-optimal dosimeter response could be falsely interpreted to mean the absence of x rays. Thus, an alternative dosimeter that provides direct dose reading display capability should be used, provided that it has been tested to provide reliable results and the wearer must be aware of any inherent limitations thereof. Direct dose-reading dosimeter results shall be recorded for individual wearers.

4.5 Survey Meter

4.5.1 Information relevant to x-ray tube based systems and electron beam welders

To avoid underestimation of the exposure rate from industrial x-ray equipment, the cross-sectional area of the radiation beam must be larger than the sensitive area of the survey meter detector. For routine survey work the meter should yield readings that are accurate to ± 20%.The energy response should be flat to within ± 20% over the desired photon energy range to be encountered. Survey meters that utilize an ionization chamber must be calibrated over the energy range for which they are to be used; calibration factors shall be used to convert the meter readings to appropriate dose values. A meter having several measurement ranges provides greater flexibility. A meter that provides maximum scale readings in the range of 10 µSv/h to 10 mSv/h (or the equivalent in exposure or dose units) is suggested. The detector response time must be short enough for an accurate radiation measurement. The meter must not exhibit "fold-back" under any circumstances. Fold-back is said to occur when an instrument is exposed to an exposure (or dose) rate or cumulative exposure (or absorbed dose) in excess of its display range and shows a lower or zero reading. Ideally, a meter that is designed against fold-back should show an off-scale deflection or, in the case of a digital display, show an overload condition when it is exposed to ionizing radiation fields that exceed the measurement range. In work areas where radio frequency (RF) fields might be present ensure that the survey meter is not sensitive to the ambient RF fields (by wrapping the meter in metallic gauze).

Several web sites may be consulted regarding radiation protection instrumentation ⁽²¹⁾ .

4.6 Emergency Response for Unintentional Radiation Exposures

Unintentional exposure to radiation may be caused by equipment failure or human error or a combination of both. Radiation accident victims must receive prompt medical attention by a physician. In addition, the root cause of the incident must be investigated and remedial measures taken to prevent recurrence at the facility. To address such situations, the facility is responsible for developing an emergency response plan and having the capabilities to implement the plan. Personnel must be trained to handle emergency equipment and to follow written procedures. The plan shall be tested and validated, and deficiencies shall be identified and corrected. The facility needs to liaise with the various personnel identified in the emergency procedures.

As a guide, the generic emergency response plan should include:

1. Response initiator - a person who initiates the response and performs actions to mitigate the accident at the scene. Usually this is the attendant radiographer or the first responder on the scene.
2. Emergency response manager - a person who is in charge of the overall plan, manages the priorities and ensures protection of other workers, emergency workers and the public. This person could be a safety officer or manager or senior staff member in the facility.
3. Radiological assessor - a person who is responsible for conducting radiation surveys and dose assessment, and for providing radiation protection support to emergency workers and advice to the facility. This person is usually the RSO or a hired consultant with relevant expertise.
   Emergency procedures should incorporate the following criteria:
   
   
   1. be concise and easy to follow;
   2. include what situations are indicative of requiring emergency action;
   3. specify the immediate action to be taken to deliver prompt medical attention to radiation accident victims or those suspect; it is advised that the attendant physician be a radiation oncologist or be knowledgeable in the biological effects of ionizing radiation on humans;
   4. specify the immediate action to be taken to minimize radiation exposure to persons in the vicinity of the radiation source;
   5. specify the names and telephone numbers of the RSO, the physician or relevant medical institution, the equipment manufacturer, the qualified expert, emergency services and the regulatory authority, and ensure that such information is up to date;
   6. notify the regulatory authority of the incident as soon as possible, and provide accurate and complete information.

The facility shall prepare a written report that contains: a description of the accident; methods used to protect other workers and the public; assessments of exposures to the accident victims, workers, emergency services personnel and members of the public; cause of the accident and corrective actions. That report shall be submitted (by the RSO) to the regulatory authority for review and follow up within 5 calendar days after the incident (see Section 2.2.1.23. of this Safety Code).

4.7 Resale of X- ray Equipment

X-ray equipment intended for resale shall also comply with the REDAct and regulations at time of sale. The seller is responsible for

1. ensuring regulatory compliance of the product and for bearing the associated costs, and
2. notifying the purchaser that it is the purchaser's responsibility to make certain that the following requirements are met before the x-ray machine can be used:
   
   
   1. the x-ray machine must be installed by trained and authorized maintenance personnel;
   2. the x-ray machine must be inspected by a radiation safety inspector authorized by the federal regulatory authority, Health Canada, and a corresponding report prepared;
   3. all operators must receive radiation safety training specific to the x-ray machine, prior to its use; and
   4. the x-ray machine shall conform to the operating rules commensurate with those of the appropriate regulatory authority that has jurisdiction of the facility in which the x-ray machine will be in use.

If the purchaser's facility is under federal jurisdiction, the Nonmedical X-Ray Unit, Consumer and Clinical Radiation Protection Bureau, Health Canada shall be contacted and the facility shall adopt this Safety Code. Otherwise, the appropriate provincial or territorial radiation protection authority shall be contacted to determine the applicable operational requirements for the x-ray machine.

4.8 Disposal of X- ray Equipment

For the disposal of an x-ray machine, the RSO shall observe the instructions provided by the manufacturer in the product manual or contact the manufacturer for information and guidance. In a case where a manufacturer is no longer in the business of manufacturing, selling or servicing industrial x-ray equipment, the following procedures shall be followed:

1. the vacuum in the x-ray tube must be breached;
2. the x-ray tube windowshould be investigated to determine whether or not it contains beryllium, and if it does, special disposal procedures must apply since beryllium presents a toxic ingestion or inhalation hazard;
3. the transformer oil, if this exists, must be disposed of in accordance with pertinent environmental legislation; and
4. the lead must be recycled accordingly.