[SystemSafety] FW: How safe is safe?

[Loebl, Andy]

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<http://www.designnews.com/profile.asp?piddl_userid=384322>
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<http://www.designnews.com/%20http:/www.designnews.com/author.asp?section_id=1395&doc_id=262577>, 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<http://apps.who.int/iris/bitstream/10665/78218/1/9789241505130_eng.pdf> 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<http://www.designnews.com/%20http:/www.examiner.com/article/fukushima-dire-warning-over-4-million-japanese-cancer-deaths%20>. 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<http://www.designnews.com/%20http:/www.nytimes.com/2013/04/02/world/asia/air-pollution-linked-to-1-2-million-deaths-in-china.html?_r=0%20>, 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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