The Search for a Safe Radiation Level for a Granite Countertop
What level of radiation is safe for a granite countertop? Using existing laws in the US, we were able to come up with some levels that might apply.
First off is a paper outlining what various states use for NORM, Normally Occurring Radioactive Material, found in the oil and gas industry. The industry seems to have an exemption allowing higher levels of radiation. From 5 pCi/g to 30 pCi/g is the range, with almost all states using the lower figure of 5 pCi/gram.
Oil and Gas equipment is allowed to be used if under 50 to 25 uR/hr above background. Gamma measurements are used because they are simple to take and inexpensive. Dose limits are taken from the IRCP and the NCRP recommended levels of 1 milliseivert per year (100 millirem per year), but both organizations recommend that the upper level should never be met, expected doses should be much less than the limit.
On yearly limits, NCRP says that anything over 5 times the yearly normal background radiation (100 millirems) needs to be mitigated, but they warn that ALARA principles should always be followed, that the goal should be significantly lower radiation than the allowed levels.
The paper concludes by recommending that levels be set at the ICRP levels of 50 pCi/g (47.5 uR/hr) for contaminated pipe and equipment, and waste and 15 pCi/g (14.25 uR/hr) for sludge and waste particles such as stone cuttings from the drilling of wells.
For remediation work such as salvaging or cleaning equipment to lower the radiation levels, the committee set a level of 30 pCi/g (28.5 uR/hr) exposure at which permission from the authorities must be obtained. They insist that some public good must come by the exposure, such as cleaning up a contaminated site, to justify the risk to the workers during cleanup.
You can view the original document here
http://www.osti.gov/bridge/servlets/purl/750593-B3YgBx/webviewable/750593.pdf
——————————————————————————————-
Another source is the EPA Project Summary that was written for the state of Florida on allowed levels of radiation in concrete for use in homes.
This study recommended the concrete was lower than 5 pCi/g (4.75 uR/hr) and that no material over 10 pCi/g (9.5 uR/hr) is used as a material.
This level may well be unobtainable by many of the granite types available. The lowest radiation level granite we have found is Absolute Black, with around 5 uR/hr after background levels are removed.
You can view the original document here
http://www.p2pays.org/ref%5C07/06324.pdf
—————————————————————————
This document details a survey of an area contaminated by Gamma radiation. Measured at a level of three feet off the ground, averaged levels of 13.8 uR/hr, with hot spots up to 27.5 uR/hr.
The study said this,
“radioactive contamination is defined as exceding the normal ambient gamma radioactivity level at one meter height by more than 5uR/hr — the criteria limit for this project.”
The original document is here
http://www.etec.energy.gov/library/D&D_page/N704SRR990034_FSDF_Baseline_Survey.pdf
Leave a Reply
You must be logged in to post a comment.
