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

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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