An investigation of the therac 25 accidents

An Investigation of the Therac-25 Accidents -- Part II

The second is the importance of providing fail-safe designs: The operator can later edit the mode and energy separately.

The computer would keep track of the machine setup and shut things down if it detected a dangerous situation. The number of pulses delivered in the 0. Abstract by Philip D.

An Investigation of the Therac-25 Accidents -- Part V

She had suffered a serious radiation burn, but the manufacturer and operators of the machine refused to believe that it could have been caused by the Therac The Therac's field-light feature permits very precise positioning of the patient for treatment.

If the operator sent a command at the exact moment the counter overflowed, the machine would skip setting up some of the beam accessories — including moving the stainless steel aiming mirror.

An Investigation of the Therac-25 Accidents

About two weeks later, the physicist at Kennestone noticed that the patient had a matching reddening on her back as though a burn had gone through her body, and the swollen area had begun to slough off layers of skin.

The actual interlock checking is performed by a concurrent Housekeeper task Hkeper.

An Investigation of the Therac-25 Accidents

Related problems were found in the Therac software. If AECL could not provide information that would guarantee safe operation of the equipment, AECL was requested to inform the users that they cannot operate the equipment safely.

Changes to tape-load error messages and check sums on the load data would wait until after the CAP was done.

Manufacturers might find that providing such information actually increases customer loyalty and confidence. They changed the CAP to have dose malfunctions suspend treatment and included a plan for meaningful error messages and highlighted dose error messages. This problem is supposedly being addressed in proposed interim revision 7A, although we are unaware of the details.

The description leaves some unanswered questions, but it is the best we can do with the information we have.

She could quickly enter prescription data and change it conveniently with the Therac's editing features. Through experimentation, he found that certain editing sequences correlated with blown fuses and determined that the same computer bug as in the Therac software was responsible.

It contained a few additions to the Revision 2 modifications, notably changes to the software to eliminate the behavior leading to the latest Yakima accident, four additional software functional modifications to improve safety, and a turntable position interlock in the software.

The electron beam would never switch on while the mirror was in place. The software set a flag variable by incrementing it, rather than by setting it to a fixed non-zero value.

Investigation After each incident, the local hospital physicist would call AECL and the medical regulation bureau in their respective countries.Description of Therac The Therac is a medical linear accelerator.

Killed by a Machine: The Therac-25

Accelerates high-energy beams that can destroy tumors with minimal impact on surrounding tissue Beam can. An Investigation of the Therac Accidents Nancy G. Leveson, University of Washington Clark S. Turner, University of California, Irvine. The Therac accidents were fairly unique in having software coding errors involved -- most computer-related accidents have not involved coding errors but rather errors in the software requirements such as omissions and mishandled environmental conditions and.

An Investigation of the Therac Accidents Nancy Leveson, University of Washington Clark S. Turner, University of California, Irvine Reprinted with permission, IEEE Computer, Vol. 26, No. 7, Julypp. Therac Accidents: An Updated Version of the Original Accident Investigation Paper (by Nancy Leveson) I have updated and changed slightly the original accident report.

An investigation of the Therac accidents Abstract: Between June and Januarythe Therac medical electron accelerator was involved in six massive radiation overdoses.

Killed by a Machine: The Therac-25

As a result, several people died and others were seriously injured.

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An investigation of the therac 25 accidents
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