Re: [SystemSafety] FW: How safe is safe?

From: Rob Alexander < >
Date: Wed, 08 May 2013 10:22:41 +0100

Hi Andy, all,

I've paged Drew Rae about this - not sure if he's on this list but validity of QRA/PRA is one of his main interests.

Drew, John McDermid about this recently published a paper on the validity of PRA --- --- in summary, there are a lot of big claims made about the value of PRA and precious little evidence to support them.


On 07/05/2013 16:24, Loebl, Andy wrote:
> I ran across this article today and while it discusses generalities, I
> thought it might be useful to some of us. I am particularly interested
> on the statement about probabilistic risk assessment. I do not much
> believe in the method because, to me, it seem like it merely reaffirms
> qualitative judgment and masks that with some assignment of numbers so
> it can look like mathematics or statistics. In any case, the article
> below is on the web today if you want to comment directly there in
> addition to here. Again, I post this not for deep debate but for
> interest and to get feedback, perhaps again, on alternatives to a PRA
> approach. The various agencies of the U.S. government seem to have
> faith in PRA and have methods for its employment. I think it has gotten
> such recognition because it seems a rather simple method and because it
> is not expensive to undertake. Further, it appears to institutionalize
> expert opinion and despite our various approaches, expert judgment is
> our bottom line, right? If there is anyone on this blog who has worked
> closely with the York people, I would like to know how they feel about
> PRA and their confidence in the numbers derived therefrom.
> Thanx
> andy
> *How Safe Is Safe Enough?*
> *Charles Murray, Senior Technical Editor, Electronics & Test*
> <>
> 5/6/2013
> One of the ugly truths of engineering is that life has a price. Cars,
> buildings, power plants, and industrial machinery can always be made
> safer for a cost, but manufacturers are at the mercy of the market.
> ”If you ask people how much money you should spend to save a human life,
> they’ll always say, ‘Whatever it takes,’” Richard A. Muller, a professor
> of physics at the University of California-Berkeley and author of the
> book /Energy for Future Presidents/, told us. “That’s not really
> rational behavior, but there’s something dry and inhuman about thinking
> through the actual numbers.”
> Indeed, there’s something cold about it. When we pointed out that the
> Fukushima Daiichi nuclear powerplant was originally designed for an
> 8.2-level earthquake a couple of weeks ago
> <>,
> some readers were incensed. Japan, they said, has a long history of
> earthquakes and its utilities should have been prepared for a 9.0. “Any
> designer who fails to look at the 100-year environment is failing to
> meet the canon of ethics,” noted one commenter on our website.
> On the flip side, the professors of nuclear engineering and physics we
> interviewed saw it differently. Considering the mammoth nature of the
> earthquake (which reportedly shifted the earth’s axis between 4 inches
> and 10 inches and took 15,000 lives), and considering the fact that the
> World Health Organization recently declared
> <>
> radiation exposure levels in the region to be low, they saw it as a
> victory for the plant’s design. “The reactor was 40-years-old and it
> stood up well,” Ahmad Hassanein, head of the nuclear engineering
> department at Purdue University, told us. “Given the situation, it did
> better than expected.”
> The disparity between those responses can be partially explained by the
> wildly differing reports emanating from the Internet. Cancer deaths in
> Japan have been projected to reach anywhere between 40 and 40 million
> <>.
> But that’s not the entire reason for the differences in belief. Much of
> the debate still comes back to those old issues of design and risk.
> Najmedin Meshkati, a professor of civil/environmental and industrial
> engineering at the University of Southern California, told us that most
> engineers simply design within the boundaries they’re given. “Engineers
> try to do a good job based on their training,” said Meshkati, who has
> studied the Bophal gas disaster, Chernobyl nuclear accident, and the
> Deepwater Horizon oil spill. “But there are issues of safety and risk
> that are beyond their level. In many cases, they’re too low on the food
> chain.” (Meshkati is currently studying Fukushima, but declined to
> comment on it.)
> Still, decisions are made. Often, the numbers depend on a process called
> Probabilistic Risk Assessment, which looks at what can go wrong, how
> likely it is, and what its consequences are, Meshkati said. In the end,
> the numbers are linked to resources, which are never unlimited on any
> project.
> In essence, that’s the nature of engineering. It’s why we don’t have $2
> million uncrashable cars that are built like tanks. It’s why houses
> succumb to earthquakes, table saws lop off fingers, and 30,000 people
> annually die on our roads. It all comes back to the question of how safe
> is safe enough? And it’s why engineers see the issues of safety
> differently than the rest of the world.
> It’s also why the professors we interviewed thought the Fukushima plant
> performed well, despite the ongoing clean-up, groundwater problems, and
> long-term evacuation. Coal
> <>,
> they said, would have killed thousands more. And the collapse of 120,000
> buildings in Japan /did/ kill thousands more. Additional resources might
> have been better directed toward the design of sturdier buildings, they
> said.
> ”Maybe you’re asking the wrong question,” Muller told us, when we asked
> how much utilities should have been willing to spend to beef up the
> Fukushima plant for a 9.0 earthquake. “Instead of asking how much you’re
> willing to spend, maybe you should ask what to spend it on.”
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Dr Rob Alexander
Lecturer in High Integrity Systems Engineering
Department of Computer Science
The University of York, Deramore Lane, York, YO10 5GH, UK
Tel: 01904 325474  Fax: 01904 325599

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Received on Wed May 08 2013 - 14:58:28 CEST

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