Radiation is Everywhere! by William O’Connell

The Radiation Safety Program is often asked to explain radiation risk to members of the public or to patients who are having medical procedures involving the application of ionizing radiation.  Expressing radiation risk in lay terms can prove challenging.  A common tool is correlating the radiation exposure required in a specific medical procedure with a similar everyday radiation exposure.  For example, a New York City resident can expect to receive 3 millisieverts from natural background radiation every year.  Therefore, if a patient is having a CT scan of the abdomen (6 millisieverts) we could say the effective radiation dose from the scan is the equivalent to the background radiation received from living in New York City for two years.  This is referred to as BERT (Background Equivalent Radiation Time).

So where does this background radiation come from?  The table below offers insight into the various sources of natural background radiation:

Source Average Annual Effective Dose
Radon Gas 2.29 millisieverts
Other Internally Deposited Radionuclides 0.31 millisieverts
Terrestrial Radiation 0.29 millisieverts
Cosmic Radiation 0.27 millisieverts
Total 3.16 millisieverts

The values cited above are average values.  Residents of Denver have higher annual doses from cosmic radiation compared to New Yorkers since the “The Mile High City” has a thinner layer of atmosphere overhead to protect it from cosmic rays.  Even the food we eat has naturally occurring radiation.  Bananas, potatoes, kidney beans, sunflower seeds and Brazil nuts all contain trace amounts of radioactivity.

Should we be worried about low-level background radiation?  The National Research Council’s Committee on Biological Effects of Ionizing Radiation (BEIR) has prepared an exhaustive study of the health effects of low levels of ionizing radiation.  In their publication, Health Risks from Exposure to Low Levels of Ionizing Radiation, the BEIR committee reviewed current research on the health effects of low-level radiation (doses less than 100 millisieverts.)  They concluded that the evaluation of radiation-induced cancer risk at doses below 100 millisieverts is difficult.  Furthermore, BEIR concluded there is no evidence of non-cancer diseases at doses below 100 millisieverts.

Individuals working with ionizing radiation are obliged by law to keep their annual dose from radiation below 50 millisieverts.  The average annual occupational radiation exposure at Columbia University is more than 10 times less and well below 5 millisieverts.  Does 5 millisieverts represent a risk-free dose?  The official answer is No – but the probability of an adverse health effect at an annual dose of 5 millisieverts is extremely small.    

After hour calls for RAM emergencies
In an effort to properly triage emergency calls received after business hours by the Radiation Safety Program (212-305-0303), EH&S will launch a voice messaging system on Friday, December 2nd that will allow callers to be routed to NYPH Security Office, CUMC Public Safety Office or NYSPI Security Office, respectively, once he/she has chosen the corresponding option within the voice messaging system. After hours the respective Public Safety and Security officers will contact applicable Radiation Safety personnel.


Editorial Staff: Kathleen Crowley, Chris Pitoscia, Paul Rubock
Graphics, Design, Lay-out: Jean Lee
Do you have a suggestion for a future  Safety Matters article? Do you have a comment on something you just read?  Please share it with us at , newsfeedback@columbia.edu

page 6 Page 6

Page 1 | Page 2 | Page 3 | Page 4 | Page 5 | Page 6

Go to Top
Go to EH&S Home Page