Answer to Question #8583 Submitted to "Ask the Experts"

Category: Industrial Radiation — Industrial Exposures

The following question was answered by an expert in the appropriate field:


What is the recommended safe distance for someone to stay away from a site where radiography is being done in the examination of steel pipes or other welding processes? In particular, how far away from the source of radiation must a person, who is not wearing a radiation dosimeter (a member of the public), be when x-ray imaging is taking place in an open area? These types of x rays would be covered by ANSI Z54.1-1963, "Safety Standard for Non-Medical X-Ray and Sealed Gamma Ray Sources," which is referred to in the OSHA regulations, like 1910.252(d)(1)(vii) and (2)(ii).


The guidance document ANSI Z54.1-1963 will tell you to set (adjust) the distance (boundary) away from an x-ray source so that a member of the public (nonbadged person) will not get more that 2 millirem (mrem) in an hour, and not more than 100 mrem in a year. A mrem is a dose of radiation; and in SI units would be 0.02 milllisieverts (mSv) in an hour, and not more than 1 mSv in a year. Each person in the United States gets an average of 7 to 8 mSv every year from medical and natural radiation exposure. The safe separation (boundary) distance depends on (1) the intensity of the x ray or gamma radiation source, (2) how long the source must be used to get a proper image (how long the x-ray machine must be turned on, or how long a gamma radiation source must out of its camera [portable-shield]), and (3) any added shielding used to reduce the radiation dose rate around the source of x rays or gamma radiation. Regulations require that a qualified radiographer must use a radiation survey meter to measure the radiation dose rate around the item being x rayed and then sets up a boundary to keep people (members of the public) away from the area so the limits (given above) are not exceeded. You can purchase the document, ANSI Z54.1-1963, from the American National Standards Institute (ANSI) at its website or from the IHS Standards Store.   

John P. Hageman, MS, CHP

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