Re: [SystemSafety] NYTimes: The Next Accident Awaits

From: Nancy Leveson < >
Date: Sun, 2 Feb 2014 07:01:15 -0500

Drew, as usual, makes much sense.

I would like to point out, however, that it seems like rail does not have an exceptionally low accident rate. At least in the past year, I have heard about a lot of very serious rail accidents in North America, Europe, and Asia.


On Sun, Feb 2, 2014 at 6:52 AM, Andrew Rae <andrew.rae_at_xxxxxx

> This may be an appropriate time to mention a paper John McDermid and I
> wrote in 2012,
> "Goal Based Safety Standards: Promises and Pitfalls". The title was
> written and promised before the paper, so it
> doesn't quite capture the fact that it is mainly about the question of
> whether it is possible, even in principle, to empirically determine
> which form of regulation works best.
> Whilst the authors are from the "other side" of the goal-based debate, it
> makes the same epistemological point as Nancy was making. We shouldn't be
> making sweeping claims about what works unless we have evidence to back
> them up. At the level of national (or even industry-by-industry) regulation
> the
> complexity of confounding factors is ridiculous. It's a hard enough
> empirical problem to determine who is actually safer let alone why.
> I think the confirmation bias issue (and review in general) is an area
> where we could do some effective experimental work.
> What types of errors are reviewers good or bad at identifying?
> Does making the safety argument explicit help or hinder a reviewer in
> finding weaknesses?
> To what extent can you "prime" a reviewer to believe a system is
> probably safe, and how does this change review performance?
> Which types of evidence actually help us tell the difference between a
> safe and unsafe system?
> There's a management science paper "Resolving scientific disputes by the
> joint design of crucial experiments by the antagonists: Application to the
> Erez-Latham dispute regarding participation in goal setting" which suggests
> that where you have entrenched scientific disputes one way forward is to
> design an experiment together.
> Whilst some of the really big questions like "which form of regulation
> works best, when" are beyond our resources to answer, it is probably worth
> thinking about what experiments (or more likely non-experiment empirical
> studies) would reveal the answers to disputes in system safety. If nothing
> else it might help find smaller questions (e.g. those I listed above) where
> we could realistically reach agreement based on evidence.
> [My own provisional view on safety cases - If they are done properly,
> there is no reason to think that they shouldn't be better than prescriptive
> regulation, because even when using prescription you still have to address
> the problem of suitability and applicability of the regulation, and there
> is no mechanism to capture this. HOWEVER, I am not at all convinced that
> any industry is consistently using safety cases properly (rail is the one
> possible exception, but there is a very heavy historical and regulatory
> background to the type of argument and evidence used inside the safety case
> framework). If my car is super-safe when driven under 40mph, but everyone
> always drives at 50mph, there's a point where I have to stop insisting it
> is a safe car.]
> My system safety podcast:
> My phone number: +44 (0) 7783 446 814
> University of York disclaimer:
> My system safety podcast:
> My phone number: +44 (0) 7783 446 814
> University of York disclaimer:
> On 2 February 2014 11:30, Nancy Leveson <leveson.nancy8_at_xxxxxx >
>> I served as an expert consultant to the Presidential Oil Spill Commission
>> after Deepwater Horizon and helped write the report. Many people at that
>> time were suggesting that all our troubles would be solved by adopting
>> safety cases. As a result, I started studying this topic in depth, read
>> everything I could find written on it, and in the end wrote a paper against
>> the use of a safety case regulatory regime in the U.S. Here are some of my
>> arguments (see the entire paper for details):
>> 1. Confirmation Bias: Confirmation bias (a well established psychological
>> principle) leads to incorrect safety cases (as have been most of the safety
>> cases that I have seen published). And reviewers suffer from the same type
>> of confirmation bias as those making up the cases. Without some way of
>> combating confirmation bias, letting people make up arguments for safety or
>> requiring certifiers to evaluate each argument individually is not going to
>> be as effective as prescriptive regulation based on historical precedent.
>> 2. Impractical Expertise Requirements on the part of Regulators: It is
>> impossible for regulators to be an expert on every type of argument and
>> analysis method that could possibly be used by an applicant. It is much
>> more difficult and more error prone to have to evaluate any possible
>> argument given. Where will such experts come from? If they exist, will they
>> really want to work for government wages (at least in the US)? I don't know
>> many people who could do this job well, including myself. So are arguments
>> simply accepted because they sound good?
>> At a meeting last year, I spoke informally with a European regulator who
>> argued that he could not regulate without the use of PRA. His argument was
>> that the systems in his industry were becoming so complex that the
>> regulators could not possibly understand the details of the systems they
>> were certifying. So they accepted probabilistic arguments by applicants
>> that performance targets would be met. I asked him how the regulators could
>> possibly know if the PRA results were correct or even reasonable if they
>> did not understand the designs that were being analyzed? He had no answer
>> for this question. In aviation, for example, it would be impossible for any
>> regulator to understand the details of the design of the entire plane in
>> order to follow an argument for why that design is safe. In addition, most
>> of these details are proprietary and therefore safety cases would not be
>> able to be open to the public or to any independent evaluation.
>> 3. Impractical Resource Requirements: The safety case approach requires
>> not only more expertise on the part of regulators, but more resources. The
>> number of government resources required to apply such a regulatory regime
>> adequately are much more than would be practical in many countries,
>> including the U.S. For example in off-shore oil drilling, the UK and Norway
>> employ a large number of highly educated personnel and technical
>> specialists to perform audits, inspections and review required documents.
>> The UK has about an equal number of off-shore oil rig inspectors as they
>> have off-shore oil rigs. In Norway, the PSA has approximately 160
>> employees, of which approximately 100 perform compliance and audit-related
>> tasks regulating 105 offshore installations. Each of these 100 employees
>> has a postgraduate (Master's degree) or equivalent level of training, in
>> one of more areas of expertise, including drilling, petroleum engineering,
>> structural engineering, and reliability engineering. In contrast, in the
>> U.S., the Bureau of Safety and Environmental Enforcement (BSEE) and the
>> U.S. Coast Guard share approximately 60 billeted offshore inspectors over
>> 3,500 offshore installations. We would never be able to hire the number of
>> people or put in the resources that the British and Norwegians do. It would
>> simply devolve into lack of any adequate regulatory oversight by U.S.
>> agencies due to lack of adequate personnel. Personnel requirements are less
>> for prescriptive regulation.
>> 4. Does it work? Is it better? There have been few objective studies
>> conducted on the impact of the safety case regulatory approach on safety
>> performance vs. other approaches. It would be nice before we engage in
>> "proof by vigorous handwaving and strong advocacy" if people would collect
>> scientific evidence of the superiority of the safety case approach over
>> others. Proponents have not done so. Note, however, that the industries
>> with the best accident statistics (such as civil aviation) do not use
>> safety cases but rather use prescriptive regulation. So a scientific,
>> comparative evaluation should be made by those advocating this approach as
>> well as ways to overcome the three practical difficulties listed above.
>> Just because it sounds good or is different than what we do now is not
>> enough.
>> Nancy
>> On Sun, Feb 2, 2014 at 4:53 AM, Tracy White <tracyinoz_at_xxxxxx >>
>>> I have found through personal experience that people with a
>>> 'certification' pedigree struggle with the concept if a safety case ...
>>> this is particularly true in defence. Where people have come from the
>>> prescriptive world which calls for completion if tasks x,y, z; their safety
>>> case is then: it's safe because we did x,y,z. This approach completely
>>> fails to justify or explain why x,y,z is appropriate or sufficient for
>>> their particular project.
>>> I do not believe that 'safety cases' provides a free for all as, in the
>>> absence of a suitable alternative, the same prescriptive sources will
>>> feature as technical safety measures. But what the safety case should bring
>>> to the table is a requirement to satisfy a claim as to why these measures
>>> (or any others) are sufficient, appropriate, applicable, relevant etc.
>>> something that prescription fails to do.
>>> Regards, Tracy
>>> On 2 Feb 2014, at 19:05, Nancy Leveson <leveson.nancy8_at_xxxxxx >>>
>>> I don't think that anyone is implying that the safety case "replaces
>>> some form of regulation". But it implies a particular form of regulation,
>>> usually performance-based rather than prescriptive. Thus ARP 4751 in
>>> aviation and MIL-STD-882 in defense, are not safety case regimes because
>>> there are specific procedures that must be followed to be certified. The
>>> applicant does not get to determine what type of argument they make.
>>> Nancy
>>> On Sat, Feb 1, 2014 at 7:43 PM, Tracy White <tracyinoz_at_xxxxxx >>>
>>>> I am slightly confused and a little perturbed by an argument that a
>>>> 'safety case' in someway replaces any regulatory control (or government
>>>> interference). Even more that a safety case would not include a subclaim to
>>>> have conducted a 'rigorous hazard analysis' program ... or to have applied
>>>> appropriate 'procedures and standards'.
>>>> Anybody who thinks that 'safety cases' in anyway replaces some form of
>>>> regulation is ignorant of its purpose. I work in a regulatory environment
>>>> and the 'safety case' is the primary communications medium with that
>>>> regulator, elements of which will talk to hazard identification and
>>>> compliance with standards and codes considered representative of
>>>> engineering 'good practice'. I would agree that there are good and bad
>>>> safety cases and I think that 'industries that do not 'have a good
>>>> historical culture in terms of safety' are as ignorant of purpose of the
>>>> safety cases as they of the need for safety in general.
>>>> Regards, Tracy
>>>> On Feb 01, 2014, at 12:48 AM, Nancy Leveson <leveson.nancy8_at_xxxxxx >>>> wrote:
>>>> It is very difficult to characterize the U.S. In general, the country
>>>> is so physically large that there are extreme differences in culture and
>>>> politics (generally but not always physically bounded). Much of the central
>>>> government in the US and European worlds seem to be moving toward
>>>> libertarianism, but I am probably mischaracterizing Europe based on biased
>>>> news reports. The individual U.S. states show extreme differences. At the
>>>> extremes, Texas and California may as well be in different worlds, let
>>>> alone countries when it comes to safety regulations (and lots of other
>>>> things irrelevant to this list). There are also such different cultures in
>>>> different industries that it is difficult to make general statements.
>>>> Mining and civil aviation are examples of such extremes.
>>>> But I will make one general statement that is only my personal
>>>> experience. Because of my paper arguing against safety cases, I am getting
>>>> many calls from government employees and company lawyers as well as
>>>> individual engineers. Some of the companies pushing the "safety case" in
>>>> the U.S. are those who don't want any government interference and see the
>>>> safety case as a way to get around the rigorous procedural standards that
>>>> now exist here in many industries. They seem to feel that they will be able
>>>> to get rid of the procedures and standards that exist now and can write
>>>> anything they want in a safety case and therefore save money and time in
>>>> the rigorous hazard analysis now widely required while using any design
>>>> features they want. These are primarily in industries that do not have a
>>>> good historical culture in terms of safety.
>>>> Nancy.
>>>> On Fri, Jan 31, 2014 at 4:08 AM, RICQUE Bertrand (SAGEM DEFENSE
>>>> SECURITE) <bertrand.ricque_at_xxxxxx >>>>
>>>>> Hi Nancy,
>>>>> Concerning France you are right, and in that case I think that the
>>>>> cultural aspect dominates. There is no safety culture in the population as
>>>>> in UK, as acknowledged after AZF accident. The risk stops at the fence of
>>>>> the plant and you can safely build your house on the other side ... The
>>>>> regulations have changed since but not the cultures. The safety engineers
>>>>> concerned by the new regulations live a nightmare as the choices are more
>>>>> or less, dismantle the plant versus dismantle the town ... I think that the
>>>>> safety cultures have more impact on the final result than the competence of
>>>>> the safety community.
>>>>> Bertrand Ricque
>>>>> Program Manager
>>>>> Optronics and Defence Division
>>>>> Sights Program
>>>>> Mob : +33 6 87 47 84 64
>>>>> Tel : +33 1 59 11 96 82
>>>>> Bertrand.ricque_at_xxxxxx >>>>>
>>>>> *From:* systemsafety-bounces_at_xxxxxx >>>>> systemsafety-bounces_at_xxxxxx >>>>> Leveson
>>>>> *Sent:* Thursday, January 30, 2014 8:59 PM
>>>>> *To:* systemsafety_at_xxxxxx >>>>> *Subject:* Re: [SystemSafety] NYTimes: The Next Accident Awaits
>>>>> It would be nice to actually introduce some data into the discussions
>>>>> on this list. First, although it is very true that the U.K. has excellent
>>>>> comparative occupational safety statistics, this exceptional performance
>>>>> predated safety cases by at least 100 years and is as much a cultural
>>>>> artifact of the U.K. as any current practices. While the rest of the world
>>>>> was suffering the results of steam engine explosions in the late 1800s, for
>>>>> example, Great Britain was the first to implement measures to reduce them.
>>>>> (I wrote a paper on this once if anyone is interested.) Although the
>>>>> British citizens on this list know more about the history of the UK HSE, I
>>>>> believe they were the first country to require companies to have safety
>>>>> policies, etc., after the Flixborough explosion. Safety cases, I believe,
>>>>> came into being only after the more recent Piper Alpha explosion.
>>>>> Trying to tie accident rates in different countries to particular ways
>>>>> of regulating safety is dicey at best. First, there are significant
>>>>> differences between the engineering, agricultural, industry, and service
>>>>> rates of accidents in countries, often related to technical differences.
>>>>> Some have high agricultural accident rates but low service accident rates.
>>>>> For example, accident rates are going to be very different in a country
>>>>> with high tech agricultural techniques compared to those still plowing
>>>>> fields with a pair of oxen. Politics plays an even more important role. For
>>>>> example, western countries often put very dangerous processes and plants in
>>>>> third world countries or governments in these countries do not have laws
>>>>> that require manufacturers to use even minimal safety practices in
>>>>> manufacturing, for example, and they will not as long as they need the
>>>>> revenue and jobs. The safety culture in these countries will not change
>>>>> magically by using one type of regulatory regime.
>>>>> Note also, that there are vast differences in industries. Those with
>>>>> the very safest records, such as the U.S. SUBSAFE program, do not use
>>>>> safety cases. (And they have managed to have an incredible safety record
>>>>> despite being in the U.S. :-)). If we want to compare the effectiveness of
>>>>> different regulatory regimes, then we need to provide scientific
>>>>> evaluations and not just misuse statistics (which may involve factors that
>>>>> have nothing to do with the actual regulatory regime used).
>>>>> Also, as Michael Holloway noted, culture differences will make
>>>>> different types of regulation more or less different in different countries
>>>>> and industries.
>>>>> Finally, I would like to point out to those who are making some
>>>>> national comparisons and putting down the U.S. in comparison with France,
>>>>> for example, that the fatal occupational accident rate in the U.S. is less
>>>>> than that of France. Perhaps we can avoid mixing politics and chauvinism
>>>>> with science on this list.
>>>>> Nancy
>>>>> On Thu, Jan 30, 2014 at 8:50 AM, Martyn Thomas <
>>>>> martyn_at_xxxxxx >>>>>
>>>>> I'm a non-exec Director at the UK's Health and Safety Laboratory (
>>>>> We carry out the basic research that underpins the
>>>>> UK's regulation of occupational health and safety, ranging from reducing
>>>>> accidents on construction sites and improving the tethering of loads on
>>>>> lorries, through to reproducing and analysing major explosions (such as
>>>>> Buncefield - and
>>>>> destruction-testing the physical integrity of tankers and rolling-stock.
>>>>> We also undertake commercial work that uses our unusual experimental
>>>>> and analysis capabilities and very strong science base.
>>>>> The UK is unusual in having a goal-based, safety-case regulatory
>>>>> regime and a regulator (HSE) with its own expert research establishment
>>>>> (HSL). We are getting an increasing number of approaches from Governments
>>>>> in the Far and Middle East who see the UK's good performance in
>>>>> occupational Health and Safety and who want to investigate setting up
>>>>> similar goal-based regulation.
>>>>> Maybe there is something in the HSE/HSL approach that the US chemical
>>>>> industry could benefit from.
>>>>> Regards
>>>>> Martyn
>>>>> Martyn Thomas CBE FREng
>>>>> On 29/01/2014 22:05, Peter Bernard Ladkin wrote:
>>>>> A worthy opinion piece from the Chair of the US Chemical Safety Board. Note his suggestion that identifying hazards and mitigation is just well-established best practice. I can say from experience that it is not yet in Europe in all industries with safety aspects, even though he holds Europe up as having a factor of three fewer chemical accidents as the US.
>>>>> _______________________________________________
>>>>> The System Safety Mailing List
>>>>> systemsafety_at_xxxxxx >>>>>
>>>>> --
>>>>> Prof. Nancy Leveson
>>>>> Aeronautics and Astronautics and Engineering Systems
>>>>> MIT, Room 33-334
>>>>> 77 Massachusetts Ave.
>>>>> Cambridge, MA 02142
>>>>> Telephone: 617-258-0505
>>>>> Email: leveson_at_xxxxxx >>>>> URL:
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>>>> --
>>>> Prof. Nancy Leveson
>>>> Aeronautics and Astronautics and Engineering Systems
>>>> MIT, Room 33-334
>>>> 77 Massachusetts Ave.
>>>> Cambridge, MA 02142
>>>> Telephone: 617-258-0505
>>>> Email: leveson_at_xxxxxx >>>> URL:
>>>> _______________________________________________
>>>> The System Safety Mailing List
>>>> systemsafety_at_xxxxxx >>>>
>>>> _______________________________________________
>>>> The System Safety Mailing List
>>>> systemsafety_at_xxxxxx >>>>
>>> --
>>> Prof. Nancy Leveson
>>> Aeronautics and Astronautics and Engineering Systems
>>> MIT, Room 33-334
>>> 77 Massachusetts Ave.
>>> Cambridge, MA 02142
>>> Telephone: 617-258-0505
>>> Email: leveson_at_xxxxxx >>> URL:
>>> _______________________________________________
>>> The System Safety Mailing List
>>> systemsafety_at_xxxxxx >>>
>> --
>> Prof. Nancy Leveson
>> Aeronautics and Astronautics and Engineering Systems
>> MIT, Room 33-334
>> 77 Massachusetts Ave.
>> Cambridge, MA 02142
>> Telephone: 617-258-0505
>> Email: leveson_at_xxxxxx >> URL:
>> _______________________________________________
>> The System Safety Mailing List
>> systemsafety_at_xxxxxx >>

Prof. Nancy Leveson
Aeronautics and Astronautics and Engineering Systems
MIT, Room 33-334
77 Massachusetts Ave.
Cambridge, MA 02142

Telephone: 617-258-0505
Email: leveson_at_xxxxxx

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