Looks very interesting, I'll have to fit it into my reading list
Doug
On Wed, Feb 23, 2022 at 5:42 PM Richard Nute <ri...@ieee.org> wrote:
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
(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> 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>
*Sent:*Monday, February 14, 2022 12:46 PM
*To:*Richard Nute <ri...@ieee.org>
*Cc:*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,”/Safetyrisk.net/ <http://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
d...@mac.com <mailto: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> 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>
*Sent:*Friday, February 11, 2022 11:37 AM
*To:*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 (Google search
<https://www.google.com/search?q=humans+are+not+very+good+at+assessing+risk>).
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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