damage than the same radiation dose delivered at lower rates. This raises further questions about comparisons to background radiation. The FDA report states: Since general-use x-ray systems emit ionizing radiation, the societal benefit of reliably detecting threats must be sufficient to outweigh the potential radiation risk, if any, to the individual screened. The dose from one screening with a general-use x-ray security screening system is so low that it presents an extremely small risk to any individual. To put the radiation dose received into perspective: Naturally occurring ionizing radiation is all around us. We are continuously exposed to this background radiation during ordinary living. In 42 minutes of ordinary living, a person receives more radiation from naturally occurring sources than from screening with any general-use x-ray security system. The national radiation safety standard (see below) sets a dose per screening limit for the general-use category. To meet the requirements of the general-use category a full-body x-ray security system must deliver less than the dose a person receives during 4 minutes of airline flight. TSA has set their dose limit to ensure a person receives less radiation from one scan with a TSA general-use x-ray security system than from 2 minutes of airline flight. A person would have to be screened more than a thousand times in one year in order to exceed the annual radiation dose limit for people screening that has been set by expert radiation safety organizations (see below). Millimeter wave security systems which comply with the limits set in the applicable national non-ionizing radiation safety standard (see below) cause no known adverse health effects. The U.S. TSA has also made public various independent safety assessments of the Secure 1000 Backscatter X-ray Scanner. Dr. David Brenner, head of Columbia University's center for radiological research, said although the danger posed to the individual passenger is "very low", he is urging researchers to carry out more tests on the device to look at the way it affects specific groups who could be more sensitive to radiation. Dr. Andrew J. Einstein, director of cardiac CT research at Columbia University, has made the following statements in support of the safety of body scanners: "A passenger would need to be scanned using a backscatter scanner, from both the front and the back, about 200,000 times to receive the amount of radiation equal to one typical CT scan ... Another way to look at