Re: How do you know it is right?
- From: "Clay S. Turner" <Physics@xxxxxxxxxxxxx>
- Date: Wed, 24 Aug 2005 21:40:35 -0400
"Jerry Avins" <jya@xxxxxxxx> wrote in message
news:c8idnWOwoJpLHJHeRVn-1Q@xxxxxxxxxx
> robert bristow-johnson wrote:
>> in article Q3NOe.49462$rp.41853@xxxxxxxxxxxxxxxxxxxxxx, Clay S. Turner at
>> Physics@xxxxxxxxxxxxx wrote on 08/23/2005 18:06:
>>
>>
>>>If you want to read about something really scary about using only
>>>software.
>>>Read the following account
>>>
>>>http://courses.cs.vt.edu/~cs3604/lib/Therac_25/Therac_1.html
>>
>>
>> i remember when that happened. i remember reading something about it at
>> the
>> time (i sure thought it was in some IEEE mag) and i think the article was
>> entitled:
>>
>> "Death by Shared Variable"
>>
>> very memorable title, IMO.
>
> I'm too lazy to read the whole article now. I too remember when it
> happened, and I learned from it. The problem boiled down to losing sync
> between the displayed dose and the internally programmed dose because the
> buggy keypad editing routine changed the first without changing the
> second. I learned from that
The other important thing was no hardware interlock was used. One was later
retrofitted, and no more accidents happened. In one of the failure modes,
the dosimeter would actually saturate and indicate low exposure, so the tech
would zap the patient again. Some patients were reported to have screamed.
Not a good sign. By the way Kennestone Hospital is only 15 miles from my
house.
Clay
.
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