Flight-time equivalent dose (FED) is an informal unit of measurement of ionizing radiation exposure. Expressed in units of flight-time (i.e., flight-seconds, flight-minutes, flight-hours), one unit of flight-time is approximately equivalent to the radiological dose received during the same unit of time spent in an airliner at cruising altitude. FED is intended as a general educational unit to enable a better understanding of radiological dose by converting dose typically presented in sieverts into units of time. FED is only meant as an educational exercise and is not a formally adopted dose measurement.
History
The flight-time equivalent dose concept is the creation of Ulf Stahmer, a Canadian professional engineer working in the field of radioactive materials transport. It was first presented in the poster session[1] at the 18th International Symposium of the Packaging and Transport of Radioactive Materials (PATRAM) held in Kobe, Hyogo, Japan where the poster received an Aoki Award for distinguished poster presentation.[2] In 2018, an article on FED[3] appeared in the peer-reviewed journal The Physics Teacher.
Usage
Flight-time equivalent dose is an informal measurement, so any equivalences are necessarily approximate. It has been found useful to provide context between radiological doses received from various every-day activities and medical procedures.
Dose calculation
FED corresponds to the time spent in an airliner flying at altitude required to receive a corresponding radiological dose. FED is calculated by taking a known dose (typically in millisieverts) and dividing it by the average dose rate (typically in millisieverts per hour) at an altitude of 10,000 m, a typical cruising altitude for a commercial airliner.
While radiological dose at cruising altitudes varies with latitude, for FED calculations, the radiological dose rate at an altitude of 10,000 m has been standardized to be 0.004 mSv/h,[4] about 15 times greater than the average dose rate at the Earth's surface. Using this technique, the FED received from a 0.01 mSv panoramic dental x-ray is approximately equivalent to 2.5 flight-hours; the FED received from eating one banana is approximately equal to 1.5 flight-minutes; and the FED received each year from naturally occurring background radiation (2.4 mSv/year[5]) is approximately equivalent to 600 flight-hours.
Radiological exposures and limits
For comparison, a list of activities (including common medical procedures) and their estimated radiological exposures are tabulated below. Regulatory occupational dose limits for the public and radiation workers are also included. Items on this list are represented pictorially in the accompanying illustrations.
| Activity | Event Type | Dose | FED |
|---|---|---|---|
| Airport x-ray full body scan | singular | 0.00001 mSv[6] | 9 flight-seconds |
| One hour of sun exposure | singular | 0.00004 mSv[5] | 36 flight-seconds |
| Household smoke detector | annual | 0.00008 mSv[7] | 1.2 flight-minutes |
| Living near a nuclear generating station | annual | 0.00009 mSv[7] | 1.3 flight-minutes |
| Eating one banana | singular | 0.0001 mSv[8] | 1.5 flight-minutes |
| Living near a coal generating station | annual | 0.0003 mSv[7] | 4.5 flight-minutes |
| Crowns or false teeth | annual | 0.0007 mSv[7] | 10.5 flight-minutes |
| Bone scan or extremity (arm) x-ray | singular | 0.001 mSv[9] | 15 flight-minutes |
| One hour of air travel | singular | 0.004 mSv[4][10][11][12] | 1 flight-hour |
| Dental (intraoral) or knee x-ray | singular | 0.005 mSv[9] | 1.2 flight-hours |
| Dental (panoramic) or shoulder x-ray | singular | 0.01 mSv[9] | 2.5 flight-hours |
| Sleeping next to someone | annual | 0.02 mSv[13] | 5 flight-hours |
| Bone scan with CT | singular | 0.04 mSv[9] | 10 flight-hours |
| Living in a stone or brick building | annual | 0.07 mSv[7] | 17.5 flight-hours |
| Chest or skull x-ray | singular | 0.1 mSv[9] | 25 flight-hours |
| Smoking cigarettes (1/2 pack per day) | annual | 0.18 mSv[14] | 45 flight-hours |
| Cervical spine x-ray | singular | 0.2 mSv[9] | 50 flight-hours |
| Mammogram | singular | 0.4 mSv[9] | 100 flight-hours |
| Pelvic x-ray | singular | 0.6 mSv[9] | 150 flight-hours |
| Abdomen or hip x-ray | singular | 0.7 mSv[9] | 175 flight-hours |
| Public dose limit | limit | 1 mSv[15] | 250 flight-hours |
| Lumbar spine x-ray | singular | 1.5 mSv[9] | 375 flight-hours |
| Background radiation in Toronto, CA | annual | 1.6 mSv[5] | 400 flight-hours |
| Brain CT scan | singular | 2 mSv[9] | 500 flight-hours |
| Background radiation - worldwide average | annual | 2.4 mSv[5] | 600 flight-hours |
| Flight crew | annual | 3 mSv[4][10][11][12][16] | 750 flight-hours |
| Neck CT or calcium scoring CT | singular | 3 mSv[9] | 750 flight-hours |
| Background radiation in Winnipeg, CA | annual | 4 mSv[5] | 1000 flight-hours |
| Thoracic angiography of heart | singular | 5 mSv[9] | 1250 flight-hours |
| Pelvic or chest CT scan | singular | 6 mSv[9] | 1500 flight-hours |
| Barium enema | singular | 8 mSv[9] | 2000 flight-hours |
| Average Fukishima recovery worker | singular | 12 mSv[17] | 3000 flight-hours |
| Abdominal angiography or aortography | singular | 12 mSv[9] | 3000 flight-hours |
| Coronary angioplasty or stent placement | singular | 15 mSv[9] | 3750 flight-hours |
| Coronary angiography | singular | 16 mSv[9] | 4000 flight-hours |
| Average annual radiation worker dose limit | limit | 20 mSv[18] | 5000 flight-hours |
| Maximum annual radiation worker dose limit | limit | 50 mSv[15] | 12,500 flight-hours |
| Pelvic vein embolization | singular | 60 mSv[9] | 15,000 flight-hours |
| Transjugular intrahepatic portosystemic shunt placement | singular | 70 mSv[9] | 17,500 flight-hours |
| Astronaut on 6 month ISS mission | singular | 72 mSv[19] | 18,000 flight-hours |
| Lowest acute dose known to cause cancer | singular | 100 mSv[20][21] | 25,000 flight-hours |