Hello Curt:
IEC 61508 series covers "functional safety." This
standard may be of use to you in your research. I've
attached a working draft of IEC TR 61508-0 which
describes the concepts of "functional safety."
(Attachments are stripped from the message by the
IEEE listserver, so listserver subscribers will not
get a copy.)
As mentioned in the case history, fault tree analysis
was used to identify causes (faults) that might lead
to a specific overexposure event. As mentioned in
the description, identifying each individual and
specific overexposure event is difficult. This is
the weakness of FTA. However, once the top event is
clearly identified, FTA is a very powerful tool to
identify the events that could cause the top event.
Relying on a single safety analysis is risky. No
safety analysis scheme such as FTA or FMEA is going
to find all the safety "problems" in the equipment.
In hardware safety, we don't rely on a single
safeguard, but on two. My advice is to not rely on
a single safety analysis, but employ at least two,
that use quite different analytic techniques. This
is the principle behind double insulation.
I much prefer the hazard-based safety engineering
processes. Identify the energy source and the means
by which energy is or can be transferred to a body
part. Then, insert safeguards to prevent either
the generation of hazardous energy, or to prevent
transfer of hazardous energy.
Software safety is used extensively in control of
airplanes. Airbus is fully fly-by-wire. They
know something about safety by means of software.
The recent 777 crash at Heathrow may have been
related to a weakness in software and might be
useful to follow the investigation.
Newer cars use software to control stability,
which is a safeguard.
Obviously, thorough follow-up of each and every
field incident report is essential to safety.
Manufacturers often have no plan for such
follow-up, and, as in the case history, marketing
(and other) folks tend to sweep such incidents
under the rug.
A colleague once remarked that a safety standard
is the inverse of bad experiences. We rarely have
safety incidents for situations covered by our
safety standards. I would guess that many
safety incidents represent problems not covered
by the standards. Other safety incidents are
due to lax follow-up in manufacturing as
exemplified by the recent recalls on toys.
Product safety is not yet an engineering
discipline.
Best regards,
Richard Nute
Product Safety Consultant
San Diego
-----Original Message-----
From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Bender,
Curtis
Sent: Wednesday, May 07, 2008 7:57 PM
To: emc-p...@ieee.org
Subject: Ethics grad work Therac-25
Greetings fellow IEEE PS forum members. I am a Grad student writing an
ethics
paper on the Therac-25 radiation machine.
http://www.computingcases.org/case_materials/therac/therac_case_intro.html
<http://www.computingcases.org/case_materials/therac/therac_case_intro.html>
My paper is focusing on the ethical situation from the manufacturer's
point
of view and hypothetically what they should or could have done differently to
solve the issue if I was their "consultant."
Primarily I am interested in the ISO/IEC or international safety
standards
for software programming of industrial equipment or medical devices. Not
necessarily to reference them but to understand the scope and to realize what
the manufacturer needed/needs to do. This would also hypothetically be
presented to the business management team that "contracted" me.
I am a little curious too as to what extent this event has taken the
existing
industry. I have read that the standards have "added unnecessary time to an
already laborious process."
I look forward, as always, to your comments.
Best regards,
Curt Bender
Curtis Bender
Tennant Company
curtis.ben...@tennantco.com <mailto:curtis.ben...@tennantco.com>
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