Answer to Question #12989 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment and Shielding — Shielding

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

Q

What is the correct way to penetrate a lead-lined x-ray room wall to install Cat6 data cabling without decreasing the lead-lined walls integrity. The wall must remain fire rated.

A

After a close reading of the question, I think I see where it comes from. While the gold standard for shielding that I would advise is National Council on Radiation Protection and Measurements (NCRP) Report No. 147, the document gets rather vague when it comes to demonstrating how to do shielding of penetrations through the lead walls. Honestly, I would recommend the old NCRP Report No. 49 that, I believe, is better at providing diagrams about how to handle penetrations.

However, reading "Cat6," I am sure you are really saying, "I cannot make sharp corners" so how do I deal with that? My experience when I am posed with these types of shielding issues in a wall is that I back off to the other side of the wall and put the shielding there. NCRP Report No. 49 actually shows you how to do this in one of the diagrams. The issue is you shield the other side of the wall with a width/height from the center of the penetration equal to twice the largest gap. In a wall built with typical 5 cm × 10 cm stud construction, that largest gap is the depth of the stud (actually 8.9 cm). So in the wall behind the room, you shield an area 18 cm from the center of the penetration and it will block the penetration hole.

So, here is the difficult one—penetrations in the floor. If the wiring is within a conduit and you can wrap the conduit through the curved portion so that there is no direct "line of sight" through the lead. (The trick is to speak with the construction people about building something that you can actually keep in place.) This is not always feasible, and you may end up needing to build a shielded box around your conduit line with an open end for the conduit to pass through. I have had to use this approach a few times in my career, but I really try to avoid it because it is difficult to build.

The one take-away message that I think will help in a "text only" response is to find a copy of the NCRP Report No. 49 diagrams. I think they will help you the most.

Jeff Brunette, CHP

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Answer posted on 13 August 2019. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.