Re: [SystemSafety] WG: words you cannot use at GM

From: C. Michael Holloway < >
Date: Thu, 22 May 2014 10:30:05 -0400

On 5/22/14 8:31 AM, Nancy Leveson wrote:
> I think saying that "acceptably safe" is safe is a ridiculous definition.
On one hand, I concur. Reusing a word in its 'definition' leads to infinite regress (as Dewi pointed out earlier concerning GM), and violates generally accepted principles of lexicography.

On the other hand, I completely disagree. "Safe" in the absolute sense (no chance whatsoever of harm) does not exist in reality. Well, except in baseball, where it is usually possible to determine conclusively whether someone is "safe" or "out." In practice, "safe" is always relative never absolute. So, it seems much more intellectually honest to admit that all discussions about safety are really discussions about an acceptable level of safety, than to pretend otherwise.

Often when I talk about safety, I show the following definition of what I mean by the word "safe": not resulting in losses to life or health (except to the extent that the number and frequency of such losses is deemed by the public to be small enough so as to be outweighed by the benefit provided). I also note that this public deeming is almost always done implicitly and may change over time. As an example, the public generally perceived commercial air travel as safe many decades ago, when the accident rate was significantly higher than it is today. Were we to return to the accident rate of several decades past today, the public would no longer consider air travel to be safe.


*C. Michael Holloway*, Senior Research Engineer
Safety Critical Avionics Systems Branch, Research Directorate
NASA Langley Research Center / MS 130 Hampton VA 23681-2199 USA
office phone: +1.757.864.1701 /often forwarded to/ +1.757.598.1707

The words in this message are mine alone; neither blame nor credit NASA 
for them.

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Received on Thu May 22 2014 - 16:30:36 CEST

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