People screening is the practice of searching people before allowing access to a secure area, for example at airports, court houses, prisons, or museums. People screening electronic products are used to detect concealed weapons, explosives or other contraband without requiring physical contact between the security screener and the person being screened.
Until recently, metal detectors were the only electronic products commonly used for people screening. However, advanced imaging technologies are also available for people screening, using either millimeter waves or x-rays.
These products are also referred to as:
- Full-body Security Scanners
- Advanced Imaging Technology
- Personnel Security Screening Systems
- People Scanners
There are two types of full-body security screening systems currently (September 2010) used by the U.S. Transportation Security Administration (TSA) at airports: general-use x-ray and millimeter wave. With each of these products, a person enters an inspection zone and remains still while the images are created. The use of these products for airport security is described on the TSA’s web site, which also addresses privacy concerns regarding the TSA’s use of these products.
General-use x-ray security screening systems deliver an extremely low dose of ionizing radiation to the person being screened. The radiation dose is so low that there is no need to limit the number of individuals screened or, in most cases, the number of screenings an individual can have in a year.
The general-use x-ray systems used by TSA are also called “backscatter” systems because they create an image from very small amounts of x-ray that have "bounced" off the person being screened. The reflected x-rays are received by an array of sensitive detectors and then processed by a computer to form an image.
Millimeter wave security screening systems use non-ionizing electromagnetic radiation. There are two types of millimeter wave security systems: active systems that expose the person being screened to small amounts of millimeter wave energy and passive systems that sense naturally occurring millimeter wave emissions from warm bodies.
General-Use X-Ray Security Systems
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
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.
- Radiation Safety Standard (x-ray)
The American National Standards Institute (ANSI) - Accredited Standards Committee N43, Equipment for Non-Medical Radiation Applications, administered by the Health Physics Society (HPS), published the current version of the American national consensus radiation safety standard for x-ray people screening products in 2009. ANSI/HPS N43.17-2009 Radiation Safety for Personnel Security Screening Systems Using X-Ray or Gamma Radiationsets limits on dose to an individual being screened; sets limits on dose to bystanders, operators, and other employees; requires a variety of safety features; and establishes operational requirements for organizations using these products. It was written, reviewed, and approved by a consensus group that included government regulators, product manufacturers, and product users.
The safety standard limits the dose per screening to 0.25 µSv (25 µrem) reference effective dose for general-use full-body security screening systems. The annual dose limit is 250 µSv (25,000 µrem) over a 12Ã¢??month period. To exceed this annual limit an individual would have to be screened more than 1,000 times in one year. This annual dose limit is in accordance with the recommendations of the National Council on Radiation Protection and Measurements (NCRP) for the annual effective dose limit for individual members of the general public (NCRP report no. 116 Limitation of Exposure to Ionizing Radiation (1993)). NCRP’s dose limitation recommendations for the general public were made with the understanding that the general public includes special populations that are more sensitive to radiation, such as children.
- U.S. Government Guidance (x-ray)
An inter-agency guidance was developed to assist Federal agencies in making consistent determinations of when the use of these products is justified. Guidance for Security Screening of Humans Using Ionizing Radiation (GSSHUIR) was published in July 2008 by the Interagency Steering Committee on Radiation Standards (ISCORS). GSSHUIR also includes basic information on how to set up an appropriate radiation safety program.
- Non-ionizing Radiation Safety Standard (millimeter wave)
The American national consensus radiation safety standard that applies to millimeter wave security systems is the Institute of Electrical and Electronics Engineers (IEEE) C95.1-2005 IEEE Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields,3 kHz to 300 GHz.
Manufacturers of any electronic product that emits radiation - including millimeter wave and general-use x-ray security systems - are required to notify FDA immediately upon discovery of any accidental radiation occurrence or radiation safety defect.
In addition, manufacturers of any electronic products that emit x-rays, including these security systems, are required to:
- submit a radiation safety report to FDA before entering products into commerce and
- file annual radiation safety reports.
Note: Manufactures that claim conformance with the ANSI/HPS N43.17-2009 Radiation Safety for Personnel Security Screening Systems Using X-Ray or Gamma Radiation safety standard should include as part of their radiation safety report:
- how the product conforms to the standard;
- category and class of their product; and
- how the manufacturer’s quality control and testing program assures that all products sold will meet the requirements of the safety standard.
For specific information on laws and regulations applicable to manufacturers of x-ray products for security screening of people, see X-Ray & Particulate Products other than Medical Diagnostic or Cabinet.
- FDA Consumer Update: Very Low Health Risks From Full-Body X-ray Scanners
- Response to University of California - San Francisco Regarding Their Letter of Concern, October 12, 2010
- NCRP Statement 10, Recent Applications of the NCRP Public Dose Limit Recommendation for Ionizing Radiation (2004)
- NCRP Commentary No. 16 - Screening of Humans for Security Purposes Using Ionizing Radiation Scanning Systems (2003)
- NCRP released a press release May 2010 regarding Commentary No. 16
- NCRP report no. 116 Limitation of Exposure to Ionizing Radiation (1993) recommends annual limits on radiation dose for the general public. Report 116 also introduces the concept of a negligible individual dose.
- NCRP report no. 160, Ionizing Radiation Exposure of the Population of the United States (2009)
- HPS Position Statement Use of Ionizing Radiation for Security Screening Individuals (2009)
- American College of Radiology (ACR) Statement on Airport Full-body Scanners and Radiation (2010)
- People screening with x-rays was discussed at several Technical Electronic Product Radiation Safety Standards Committee (TEPRSSC) meetings. The last discussion took place during the October 1, 2003 meeting.
- Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 (2006)
- Assessment of the Rapiscan Secure 1000® Body Scanner for Conformance with Radiological Safety Standards. July 21, 2006, produced for TSA, measurements made at FDA, report completed at NIST
- Radiation Safety Engineering Assessment Report for the Rapiscan Secure 1000 in Single Pose Configuration, Johns Hopkins University Applied Physics Laboratory, Assessment for TSA, October 2009 and revised August 2010