Mark, I did something along those lines back in 2012 when a question came up about the need for a finger guard on a low power fan. In order to better understand the possibility of injury, I estimated the surface contact area of the blade edge against a finger, rotational speed and mass of the fan impeller in terms of mechanical energy. I think I converted to J/mm^2. In any case, the result was quite low and in my opinion "safe". To prove it out, I was willing to first try jamming a #2 pencil, and then my finger into the fan while running at full speed. So far, 10 years later, I still have my fully intact finger, but sadly the pencil was eventually used or otherwise lost.
-Doug Douglas E Powell Laporte, Colorado USA doug...@gmail.com LinkedIn <https://www.linkedin.com/in/coloradocomplianceguy/> (UTC -07:00) Mountain Time (US-MST) On Wed, Feb 23, 2022 at 4:04 PM Mark Ortlieb <mark.ortl...@braincorp.com> wrote: > Hello all, > > I am keenly interested in this discussion on energy vs energy/time with > respect to causing injury, especially from a physical contact perspective. > A couple of other considerations that are worthy to be included in such a > discussion, which would add another layer of complexity would be: > > - The geometry of the object that comes into contact with the body. > Take a needle as an example, or a knife edge. Let's say the needle is very > light (a gram or two) and moving very slowly (1 mm/hour), at some point > severe injury could take place through piercing of skin. Real world > scenario aside, this illustrates a different kind of potential harm that > can be inflicted. I don't know if there is a practical way to incorporate > such a factor into an equation (such as the Energy Transfer equation), but > certainly it needs to be included as part of a thorough analysis. > - The kind of "victim" person being considered, for example a child vs > an adult. A child may not be able to withstand the same level of energy > transfer as an adult, or may be subject to a different kind of injury as > the result of an energy transfer, that is, a secondary injury, such as > being more easily pushed down and hitting their head on the floor. In fact, > I am interested to know if there are others out there who are aware of any > data or studies regarding impact with children. > > Thanks, > > Mark > > > > > > > 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> <d...@mac.com> > *Sent:* Monday, February 14, 2022 12:46 PM > *To:* Richard Nute <ri...@ieee.org> <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 > > “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/). > > > > -Doug > > > > Douglas E Powell > > Laporte, Colorado USA > > - > ---------------------------------------------------------------- > > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to < > emc-p...@ieee.org> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) <http://www.ieee-pses.org/list.html> > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org> > David Heald <dhe...@gmail.com> > > > - > ---------------------------------------------------------------- > > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to < > emc-p...@ieee.org> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) <http://www.ieee-pses.org/list.html> > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org> > David Heald <dhe...@gmail.com> > > -- > [image: Brain Corp] <https://www.braincorp.com> > Mark Ortlieb > > Senior Engineer, Regulatory > Brain Corp > > 858-207-7591 > braincorp.com <https://www.braincorp.com> > > 10182 Telesis Ct, Suite 100 > San Diego, CA 92121 > [image: Brain Corp LinkedIn] > <https://www.linkedin.com/company/brain-corporation> [image: Brain Corp > Twitter] <https://twitter.com/braincorp> [image: Brain Corp YouTube] > <https://www.youtube.com/user/thebraincor/> > - > ---------------------------------------------------------------- > > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to < > emc-p...@ieee.org> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) <http://www.ieee-pses.org/list.html> > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org> > David Heald <dhe...@gmail.com> > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
