Answer to Question #1979 Submitted to "Ask the Experts"

Q

My company recently installed a baggage/package x-ray device. The state inspection requires I post for my employees what the symptoms of acute x-ray exposure are. Although this device is classified as a minimal threat, can you provide me what symptoms would appear if acute or long-term exposure occur?

A

Acute effects of radiation require large doses delivered in short times. The minimum threshold dose for such effects is 250 mSv, for transient depression of blood white cell and platelet counts. The likelihood of your machine delivering this dose in a brief period ranges between slim and none. Other acute effects require still larger doses: radiation sickness, skin erythema and dermatitis, hair loss, sterility, acute radiation sickness, etc. All of these doses apply to uniform doses to the whole body. The concern for occupational exposures in situations such as yours is for long-term or delayed effects: cancer and mutation. These effects are stochastic in nature; the probability of occurrence is approximately proportional to dose. The current whole-body occupational dose limit in the United States is 50 mSv per year, with a recommended accumulated limit of the individual's age in years multiplied by 10, with the product expressed in mSv. Only adults are permitted any occupational dose. This dose is well below the threshold for acute effects and places the resulting probability of delayed effects at levels well below which insurance companies rate occupational risks as hazardous. In other words, radiation work is regarded as a safe occupation. There are also higher occupational dose limits to certain body parts (skin, hands, eyes) that are much greater. These further limit resulting acute effects. Pregnant radiation workers are limited to occupational doses of 0.5 mSv per month during pregnancy. The fetus is far more sensitive than adults. Most state laws and regulations require that persons occupationally exposed to radiation wear personal radiation monitors while working, with a few exceptions. You may be well advised to provide these monitors for your workers. The resulting peace of mind is well worth the nominal cost. S. Julian Gibbs, DDS, PhD