A.11. Radiation

In the course of operation, most system will emit—and be subject to—various forms of radiation, especially electromagnetic radiation in the radio spectrum due to the frequencies in clocks that control bus speeds, CPU speeds, screen refresh rates, and so forth. Emitted radiation must be limited to avoid interference with other devices, and incoming radiation that is within normal limits should not interfere with the operation of this device.

Some radiation can be more magnetic than electromagnetic. Computer-controlled magnetic resonance imaging (MPJ) medical systems have been involved in fatalities when their powerful magnetic fields caused ferrous (iron-based) metal objects to abruptly fly through the air and strike occupants and bystanders with tremendous force. One patient was killed by a flying oxygen tank, and a police officer's gun was involved in another incident.

Some systems are designed to emit radiation, such as nuclear medicine devices like the Therac-25. You might recall the horrifying anecdote I related about this device's failures in Chapter 1, "Defining What's on Your Plate: The Foundation of a Test Project," where software bugs interacted to result in fatal dosages delivered to some patients. The United States Department of Defense in now considering the construction of extremely high-powered lasers mounted on aircraft for the purposes of shooting down ballistic missiles, and the United States Department of Energy is replacing the nuclear testing ...

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