Hi Doug:
See:
https://www.tandfonline.com/doi/pdf/10.1080/01446193.2016.1274418?needAccess=true
Best regards,
Rich
From: Douglas Nix <d...@mac.com>
Sent: Wednesday, February 23, 2022 8:57 AM
To: Richard Nute <ri...@ieee.org>
Cc: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Risk assessment versus HBSE
Hi Rich,
Your points are well taken.
There are some good ISO standards that relate to exposure to hot and cold
temperatures. These standards take the type of material, and therefore the
transfer rate, of heat into account and are quite useful IMO.
You are right about the HBSE model, and I think that we need both approaches,
that is HBSE and “conventional” risk assessment. The issue is always this: what
do you do when you don’t have any data? Practitioners must start with what they
know, and that usually means starting with qualitative risk assessments. This
is especially true in the broader OHS sector where these types of assessments
are used for workplace inspections. The problem is that when we attach
arbitrary numeric values to qualitative scales people start to believe that the
math is somehow “right” regardless of how arbitrary in the input data. Even if
the math is correct, GIGO. This is what plagues the application of conventional
risk assessment techniques and why Cox, Quintino and others have been raising
the alarm for so many years.
We’re now in a place where the EU has a semi-quantitative (yes I hate that term
too, but it’s descriptive) risk assessment tool built into the RAPEX directive
for use on consumer products and white goods. This same tool has been adopted
by the US CPSC, although they are not making this widely known. Health Canada
has their own methodology for the same purpose, and I’m quite sure that if we
were to examine the methods used by the national health and safety agencies in
any country that has such an entity, we would find that they too have some
method like the RAPEX/CPSC or Health Canada methods. So, for now we are stuck
with what we have. At least we are getting manufacturers to think about risk,
rather than “just” hazards.
Progress comes slowly…
--
Doug Nix
d...@mac.com <mailto:d...@mac.com>
(519) 729-5704
"Opportunity is missed by most people because it is dressed in overalls and
looks like work." - Thomas A. Edison
On 22-Feb-22, at 19:03, Richard Nute <ri...@ieee.org <mailto:ri...@ieee.org> >
wrote:
Hi Doug:
Thanks for your comments.
What bothers me about risk assessment is that the committees that have written
the standards requiring risk assessment have not critically evaluated the risk
assessment process. If they had done so, we would not have the process as we
know it today.
Actually, I do not fully agree with the Gibson finding that energy causes
injury. I can show that the injury parameter is energy per unit time, e.g.,
joules/second. The body can absorb energy slowly without injury, but not
quickly. Consider that a car with people in it can brake or stop without
causing injury to the passengers, but cannot “crash” to a stop where injury is
likely. In both cases, the kinetic energy to stop is the same, but the kinetic
energy per time to stop is low in braking, but high in crashing.
The attached picture is that of catching three objects and assumes the
deceleration time is the same for each object. Note that when we catch an
object, we can catch it “slowly” and distribute the energy over a longer time
than catching it “directly.” I submit this as proof that energy per unit time
is the parameter that causes injury.
HBSE does indeed have (or can have) energy criteria for each form of energy.
However, I agree that some energy data is not readily available and must be
researched. And, using the energy model can be quite complex. For example,
injury from thermal energy is often simply taken as accessible temperature,
sometimes including a time of contact. Using a single parameter, temperature,
or including time of contact parameter, does not address the difference between
an aluminum block and aluminum foil (which is the issue some members of IEC
TC108/HBSDT are addressing). Or the difference between an aluminum block and
a plastic block.
Best regards,
Rich
From: Douglas Nix <d...@mac.com <mailto:d...@mac.com> >
Sent: Monday, February 14, 2022 12:46 PM
To: Richard Nute <ri...@ieee.org <mailto:ri...@ieee.org> >
Cc: EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG>
Subject: Re: [PSES] Risk assessment versus HBSE
Hi Rich,
I have to admit that I’ve been thinking about your reply all weekend.
As you know, I teach machinery risk assessment and consult in this area
regularly. I want to stipulate that there are some significant issues with risk
assessment the way it is most commonly applied in industry, see my list of
references on this topic at the end of my message.
The inherent subjectivity of risk assessments that are performed without
empirical data is unquestioned. The difficulty is that for many areas of human
endeavour we have no empirical data, and try as we might we cannot calculate
without numeric data. Nevertheless, we must be able to make risk-based
decisions when designing products and equipment, and so we muddle along with
the best tools that we have, hopefully while recognizing their flaws.
The HBSE model is a good one, and it fits machinery applications as readily as
does risk assessment, however, the risk assessment methods that are used today
have a history that stretches back to the 1960s, while the HBSE model is much
younger. This doesn’t take away from HBSE in any way for me, but it does have
an impact on the broader acceptance of the method since it is not yet as widely
known as “conventional” risk assessment. None of the the standards in the
machinery safety sector recognize the method as yet, so getting regulators and
users to consider the method is a challenge.
HBSE also suffers from issues with lack of data when it comes to characterizing
some hazards, leaving the user to estimate the characteristics. This brings in
the biases of the person(s) doing the estimating just as surely as conventional
risk assessment methods.
The absence of a probability parameter in the HBSE model is an interesting one,
since the probability aspect is the one most subject to error in conventional
risk assessment. Humans are notoriously bad at estimating probability. It
appears to me that the absence of that parameter implies that the presence of a
hazard will inevitably lead to harm, which I don’t disagree with. CSA Z1002,
OHS risk assessment, actually states that this is the case, and recommends that
hazards are eliminated on this basis whenever possible.
So we’re left with this situation, I think:
1) Risk assessment, when done quantitatively using sound statistical techniques
and valid data is a useful and relatively objective method to provide data to
decision makers,
2) Conventional risk assessment using subjective opinions and risk matrices or
decision trees are unrepeatable and therefore unscientific, however. despite
their flaws, they provide a means to help guide decision makers,
3) HBSE improves on some aspects of conventional risk assessment by eliminating
the probability parameters, but is still subject to some subjectivity, and is
still not widely accepted enough for some decision makers.
I wish there was a more utopian perspective to take on the topic, but I have
yet to find my way to it.
References
[1] E. S. Levine, “Improving risk matrices: The advantages of logarithmically
scaled axes,” J. Risk Res., vol. 15, no. 2, pp. 209–222, 2012.
[2] R. Long, “Calculators , Matrices and Mumbo Jumbo Risk Assessment,”
<http://safetyrisk.net/> Safetyrisk.net, 2016. [Online]. Available:
http://www.safetyrisk.net/calculators-matrices-and-mumbo-jumbo-risk-assessment/.
[Accessed: 03-Feb-2016].
[3] D. J. Ball and J. Watt, “Further Thoughts on the Utility of Risk Matrices,”
Risk Anal., vol. 33, no. 11, pp. 2068–2078, 2013.
[4] C. Bao, D. Wu, J. Wan, J. Li, and J. Chen, “Comparison of Different Methods
to Design Risk Matrices from the Perspective of Applicability,” Procedia
Comput. Sci., vol. 122, pp. 455–462, 2017.
[5] C. Peace, “The risk matrix : uncertain results?,” Policy Pract. Heal. Saf.,
vol. 0, no. 0, pp. 1–14, 2017.
[6] B. Ale and D. Slater, “Risk Matrix Basics,” 2012.
[7] P. Gardoni and C. Murphy, “A Scale of Risk,” Risk Anal., vol. 34, no. 7,
pp. 1208–1227, 2014.
[8] P. Baybutt, “Guidelines for Designing Risk Matrices,” Process Saf. Prog.,
vol. 00, no. 0, p. 7, 2017.
[9] H. J. Pasman, W. J. Rogers, and M. S. Mannan, “Risk assessment: What is it
worth? Shall we just do away with it, or can it do a better job?,” Saf. Sci.,
vol. 99, pp. 140–155, 2017.
[10] X. Ruan, Z. Yin, and D. M. Frangopol, “Risk Matrix Integrating Risk
Attitudes Based on Utility Theory,” Risk Anal., vol. 35, no. 8, pp. 1437–1447,
2015.
[11] S. Albery, D. Borys, and S. Tepe, “Advantages for risk assessment:
Evaluating learnings from question sets inspired by the FRAM and the risk
matrix in a manufacturing environment,” Saf. Sci., vol. 89, pp. 180–189, 2016.
[12] P. Thomas, R. B. Bratvold, and J. E. Bickel, “The Risk of Using Risk
Matrices,” SPE Annu. Tech. Conf. Exhib., no. April 2015, 2013.
[13] F. Gauthier, Y. Chinniah, D. Burlet-Vienney, B. Aucourt, and S. Larouche,
“Risk assessment in safety of machinery: Impact of construction flaws in risk
estimation parameters,” Saf. Sci., vol. 109, no. June, pp. 421–433, 2018.
[14] O. Amundrud and T. Aven, “On how to understand and acknowledge risk,”
Reliab. Eng. Syst. Saf., vol. 142, pp. 42–47, 2015.
[15] S. O. Hansson and T. Aven, “Is Risk Analysis Scientific?,” Risk Anal.,
vol. 34, no. 7, pp. 1173–1183, 2014.
[16] J. Li, C. Bao, and D. Wu, “How to Design Rating Schemes of Risk Matrices:
A Sequential Updating Approach,” Risk Anal., 2018.
[17] L. A. Cox, D. Babayev, and W. Huber, “Some limitations of qualitative risk
rating systems,” Risk Analysis, vol. 25. pp. 651–662, 2005.
[18] L. A. Cox, “What’s wrong with risk matrices?,” Risk Anal., vol. 28, no. 2,
pp. 497–512, Apr. 2008.
[19] A. Quintino, “What’s Wrong with Risk Matrices? Decoding a Louis Anthony
Cox paper Reshaping dowsntream configuration View project An integrated risk
management model for an oil and gas company View project,” no. March 2011, 2016.
--
Doug Nix
<mailto:d...@mac.com> d...@mac.com
“If there are no dogs in Heaven, then when I die I want to go where they went.”
-Will Rogers
On 12-Feb-22, at 16:59, Richard Nute <ri...@ieee.org <mailto:ri...@ieee.org> >
wrote:
I don’t like the Risk Assessment process because it is highly subjective and
not very repeatable.
When I was with Hewlett Packard, three of us developed “Hazard Based Safety
Engineering,” HBSE. The basis for HBSE was James J. Gibson’s (Cornell
University) research into child injury from auto accidents. Gibson said:
“Injuries to a living organism can be produced only by some energy interchange.
Consequently, a most effective way of classifying sources of injury is
according to the forms of physical energy involved. The analysis can thus be
exhaustive and conceptually clear. Physical energy is either mechanical,
thermal, radiant, chemical, or electrical.”
In a moving automobile, the automobile and its passengers have kinetic
(mechanical) energy. In an accident, the kinetic energy of the automobile is
dissipated in crumpling parts. The kinetic energy of the passengers is
dissipated in injuries to the body. Seat belts transfer the passenger kinetic
energy to the automobile. Air bags slow the rate of kinetic energy transfer to
the automobile.
HBSE identified the magnitudes each kind of physical energy necessary to cause
injury. We called this “hazardous” energy. Then, HBSE went on to specify
safeguards that would attenuate or prohibit hazardous energy interchange.
When I evaluate a product, I look for the physical energy sources, and then
determine if the energy sources are hazardous or not. Unlike Risk Assessment,
this is easy and repeatable and not subjective. For example, all primary
circuits are hazardous energy circuits that can cause injury (electric shock,
thermal, fire, and maybe more) and safeguards must be provided.
Best regards,
Rich
From: Douglas E Powell <doug...@gmail.com <mailto:doug...@gmail.com> >
Sent: Friday, February 11, 2022 11:37 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG>
Subject: Re: [PSES] EN 62368-1 : 2020 Ed 3
In my view, the Risk Assessment should never be treated as a 'get out of jail'
card or panacea. Instead, it is only a starting point for a safe design and
should be done near the beginning of a project, not the end. I agree with what
Rich says, I've seen a lot of subjective assessments by cross-functional teams,
with variability based on personal risk tolerance or risk aversion. There are
any number of articles pointing to why humans are not very good at assessing
risk (
<https://www.google.com/search?q=humans+are+not+very+good+at+assessing+risk>
Google search).
When using FMEA for risk assessment, I always stress that the RPN factors of
probability of occurrence, severity, and detection be quantified separately
without regard to the other factors, not an easy task. There is also the
problem of RPN vs Criticality (severity x occurrence). If using the RPN, there
is the possibility that Detection can dilute the RPN number to a point below
the threshold for action. So in my view, Criticality alone should be used to
trigger action.
Kenneth Ross wrote a very good article last month on Navigating the Safety
Hierarchy; for me, it was an excellent refresher on how I should use risk
assessment more effectively (
<https://incompliancemag.com/article/navigating-the-safety-hierarchy/>
https://incompliancemag.com/article/navigating-the-safety-hierarchy/).
-Doug
Douglas E Powell
Laporte, Colorado USA
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