The Risks Digest

The RISKS Digest

Forum on Risks to the Public in Computers and Related Systems

ACM Committee on Computers and Public Policy, Peter G. Neumann, moderator

Volume 3 Issue 5

Tuesday, 10 June 1986


o A powerful metal detector and magnetic personalities with bank cards
Matthew P. Wiener
o Shuttle Launch Decisions
Don Wegeng
o Re: Estell's defense of SDI
Martin Purvis
o Sgt. York's Latrine, and other stories
Mike McLaughlin
o Info on RISKS (comp.risks)

A powerful metal detector and magnetic personalities with bank cards

Matthew P. Wiener <>
Sat, 7 Jun 86 02:27:54 pdt
    [This item illustrates the need for awareness of the technology by people
     in the environment.  The interference problem is also relevant to RISKS.]

In the Thursday 5 June 1986 issue of The New York Times, there is an article
about an accident that occurred with a magnetic resonance imager--the first
serious accident of this type.

The device uses a huge magnet with a hollow cylinder for the patient to lie
inside.  The accident occurred in a converted semitrailer used for mobile
diagnosis.  A technician was in the hollow when two steel tines, weighing
more than 80 pounds each, were ripped off by the magnet from an
(intentionally) approaching forklift, and ended up knocking the man 15 feet
away, and breaking many bones.

The magnet complicated rescue work.  A doctor could not approach until he
removed his stethoscope.  A paramedic's scissors flew off when he tried to
cut the injured man's pants.  A policeman nearly had his gun pulled from his
holster.  Rescuers were slow to grasp just how strong the magnetic field
was, and to realize that all metal objects had to be removed in order to
approach the injured.  And finally--here's where the computer connection
comes in!--the magnetic bank cards of the rescuers were erased.

The magnet's emergency shutdown could not be used, as it hadn't been fully
installed yet.  So it took 20 minutes instead.

The article pointed out that in normal usage these difficulties are not
present, as normally special equipment is used and all nearby personnel are
familiar with its power.  But as revealed by the accident, emergency workers
do not have such training.  (They also do not have training for lots of
special and exotic situations.  There is a certain iatrogenic irony
in this situation — which is not uncommon in medical practice.)

          ["Iatrogenic" implies that a problem is caused or made worse
            inadvertently by doctors and/or medicine in what might 
            otherwise be perceived as an attempted cure or improvement.
            [[As a result, one suffers from inadvertigo?]]  The use of
            "irony" seems like an attractive pun in this context.  
            Thanks.  PGN]

Note--some details are slightly unclear from the article I read.  If anyone
wants more details, you are referred to a recent letter in The New England
Journal of Medicine, by(?) Drs. Syverud and Fowler.   -Matthew

ucbvax!brahms!weemba    Matthew P Wiener/UCB Math Dept/Berkeley CA 94720

Shuttle Launch Decisions

dw <Wegeng.Henr@Xerox.COM>
10 Jun 86 09:00:41 EDT (Tuesday)
After watching the reports on TV giving the conclusions of the Rogers
Commission, a question occurred to me that may be relevant to Risks. A lot
of attention has been given to the fact that some of the rocket engineers
recommended against launching the Challenger. What I haven't heard anyone
talk about is whether such recommendations before a launch were common. The
media coverage has always implied that the engineer's protests were an
unusual event, but is this really the case? I can easily imagine a scenario
where before every launch a different engineer recommends against launching,
but management decides that their reasons are not adequate (after all, one
of management's jobs is to evaluate such recommendations) and goes ahead and
launches as scheduled. After awhile the situation might become similar to
the little boy who cried wolf.

I'm not trying to defend NASA, or implying that the above scenario
describes the situation. I'm just trying to understand the context of
their decision to launch Challenger. Can anyone shed any light on this?

       [I hope one of our readers can respond.  With regard to the software
        problems, there have been complaints that the new mission software
        was frequently delivered only at the very last minute, and that no
        extensive simulation testing could be done.  The impression is given
        that whatever the state of the software was at the final scheduled
        delivery date, that is what was delivered — irrespective of how
        buggy it might be.  I think it would be very helpful to understand
        the circumstances better.  Tasteful reports on this subject — as
        well as the more general question raised by Don — would be welcome.

Re: Estell's defense of SDI

Tue 10 Jun 86 21:57:50-CDT
Estell makes the following comment:

  The "complexity" and "historical" arguments even interact.  
  Peter Denning observed years ago that the difficulty of understanding a 
  program is a function of size (among other things).  He speculated that 
  difficulty is proportional to the SQUARE of the number of "units of under-
  standing" (about 100 lines of code).  Old tactical software, in assembly 
  language, tends to run into the hundreds of thousands of lines of code; 
  e.g., a 500,000 line program has 5000 units of understanding, with a diffi-
  culty  index of 25 million.  That same program, written in FORTRAN, might 
  shrink to 100,000 lines thus only 1000 units of understanding, thence a 
  difficulty index of one million.  That's worth doing!

I believe that the same program written in a "high level" language,
like Fortran, would probably have about the same number "units of
understanding" ~ 5000, in this case.  Assuming that the "units of
understanding" are understood to be higher level concepts, Fortran
would enable one to write those units with fewer lines of code.  But I
wouldn't expect the number of those units to decline with nearly the
same scale factor.

Of course the likelihood of a typographical error would be reduced by
such a scale factor, but that's not the major concern here.

--Martin Purvis

Re: Sgt. York's Latrine, and other stories

Mike McLaughlin <mikemcl@nrl-csr>
Tue, 10 Jun 86 12:36:24 edt
I believe there were several retractions - enough for me to believe, at any
rate.  If I hadn't been so tired when I sent that bit to Peter I would have
expounded further on the delightful topic of various matters hitting the
fan, etc.

I *hope* that whoever designed the helicopter-rotor-selection algorithm did
more than simply search for cyclic doppler.  There are too many things out
in the real world that rotate but aren't helicopters.  
    - Wind turbines on a barn
    - The rotating beacon at some airports
    - Windmills
    - Cooling fans on the roof of a large building
    - Cooling fans on top of a diesel/electric locomotive 

By the way, I have patronized a fair number of outhouses down in the Shenandoah
Valley - While almost all needed (desperately!) ventilating fans, only one or
two had them - and they sounded like squirrel cage blowers within a ventilating
pipe, not likely to be picked up by Sgt. York's radar.  Nose yes, radar no.

    - Mike McLaughlin   <mikemcl@nrl-csr>

                 [I understand that, inspired by these reports, particle
                  physicists are now working on a new approach: Latrinos.  
                  Note: I expect that future submissions to RISKS on this 
                  subject will get flushed.  (Please replace all DIVADs.)

Please report problems with the web pages to the maintainer