[SystemSafety] WG: words you cannot use at GM

[C. Michael Holloway]

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.
-- 
/*cMh*/

*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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