Answer to Question #8626 Submitted to "Ask the Experts"

Q

What protocols or guidance is appropriate for operational checks of safety equipment (e.g., interlock testing, warning lights, etc.) for electronic devices that produce ionizing radiation? The question arises because of bench-top units that could be damaged by improper ramping up or shutting off the high voltage or from devices that generate soft x rays that are difficult to detect with standard radiation detection equipment.

A

Depending on the institution where you are working, you may be under a Department of Energy or Nuclear Regulatory Commission regulation, and the state regulations if you are not in an agreement state. The following standards and reports provide information on the protocol that should be followed for testing radiation generating safety devices.

Please note that if you are producing x rays with energies higher than 10 keV, there are radiation detectors on the market that can give you a dose rate reading, which would be needed for the level of safety program that you may need to implement.

For the safety interlocks that cannot be tested every time before use, for example at large accelerators or the device that you are concerned with, the general consensus is that your radiation safety interlocks have to be tested biannually. Of course you will need to come up with a test procedure that will test the interlock safety devices without damaging the devices they are trying to protect. The procedure has to be review and approved by a system expert to demonstrate that you are adequately testing all the aspects of the radiation safety interlock system. The testing procedure should be acceptable by whatever regulatory agency that your institution/laboratory/company is required to comply with.

The following standards can provide guidance for the table top nonmedical devices:

• ANSI N43.3-2008, American National Standard For General Radiation Safety - Installations Using Non-Medical X-Ray and Sealed Gamma-Ray Sources, Energies Up to 10 MeV  (available for free from the Health Physics Society.
• Radiation Alarm and Access Control Systems, NCRP Report 88, National Council on Radiation Protection and Measurement, Washington, DC; 1986
• The DOE guidance DOE G 441.1-5  gives details of program/protocol to control such devices.

The following references are also useful for the radiation safety interlocks:

• Application of Safety Instrumented Systems for the Process Industries, ANSI/ISA - 84.00.01 - 2004.
  
• Health Physics Manual of Good Practices for Accelerator Facilities, US DOE Report SLAC-327, April 1988. (free from SLAC).

Best regards,

John E. Anderson, Fermilab AD Safety Department Head

Kamran Vaziri, PhD