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 Post subject: Types of Risk
PostPosted: Mon Jan 26, 2015 7:03 am 
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In the recent posting on risk assessment that I did, I used the term "acceptable risk". In a private E-mail, we got off on the subject of this term. I've been using and seeing the term "acceptable risk" for over a decade amongst different companies. It was pointed out that the term "acceptable" is repugnant, and an alternative, "residual risk" was proposed.

The term "residual risk" is used in ANSI/RIA R15.06, "For Industral Robots and Robot Systems -- Safety Requirements". This is the risk analysis procedure maintained by the Robot Industries Association (RIA). Frankly for mechanical/moving equipment hazards, it is the best in class. In this system one first calculates the initial "risk" which in 70E terminology would be "hazard/risk" since both the injury magnitude and likelihood are converted into a combined score such as "R2a", assuming that there are no safeguards in place. Then after applying safeguards the risk is analyzed again on a slightly different table to determine a new "residual risk". The second table is slightly more relaxed. The process is repeated until the residual risk score meets the passing criteria for, and here I have to say it, acceptable risk.

The terms "tolerable risk" and either "negigible risk" or "acceptable risk" are used in the UK Health and Safety Executive standard. Many other companies also use these same terms. "Tolerable risk" is defined as the maximum allowable risk even after efforts have been taken to lower it. The UK Health and Safety Directive took the level from injury rates in "high risk" industries (fishing, logging, etc.). Negligible risk is somewhat more nebulous in its definition but is essentially the total opposite...the risk inherent to the public from all sources. The term "acceptable risk" is also used in that the "negligible risk" level is defined as acceptable under any circumstance. In other words, we should first analyze the risk with no protection in place. Then if it is higher than "negligible risk" (which is effectively automatically accepted), we then apply various protections following ALARP (as low as reasonably practicable) until the residual risk is below the negligible risk level. If all reasonable/practical protections are exhausted so long as the remaining residual risk is below the tolerable risk level then this is also acceptable.

This EU safety is focussed on prevention rather than getting overly concerned with protection (PPE).

Outside of say UK HSE territory, my recommendation would be to look at a third term, comparable risk. For instance accoridng to CCPS high risk industry rates are at 0.0001/year while low risk (engineering, clerical) injury rates are 0.00001.. So setting an acceptance criteria (avoiding that "acceptable risk" term here) of somewhere in that range would mean in this case that we are adopting a comparable risk criteria as an acceptable rate.

If we go down the path of using the word "acceptable risk" then we are on the slippery slope argument and the "zero risk" crowd shows up and drives the acceptance criteria down to silly levels. to where what is acceptable for electrical work is vastly safer than what is acceptable for all other work going on around the area. Using the term "comparable risk" drives home this point, avoids terms that have already been defined elsewhere, and emphasizes the point that the goal is to make electrical work no more and no less safe than any other work. In practice we don't have enough data so that we will be implmenting a criteria that is looking at worst case and setting the standard based on this so the average case is far better and it's still safer than other activities.


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 Post subject: Re: Types of Risk
PostPosted: Thu Jan 29, 2015 5:14 am 
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Joined: Sun Sep 23, 2007 5:00 pm
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Location: Calgary, Alberta, Canada
Great post, lots of detail.

We need to keep the Risk Assessment Procedure (RAP) as simple as possible for a Qualified Electrical Worker to implement against an approved, authorized and justified energized electrical work task.

And yes it can be done.

I agree with the detailed explanation, but the minimum requirement when using CSA Z462-15 as the referenced Standard is developing a process consistent with Annex F.


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 Post subject: Re: Types of Risk
PostPosted: Thu Jan 29, 2015 10:47 am 
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Annex F is informative, not required. And you can't implement it. In the last Code cycle it was so bad that I even submitted a request to simply delete it and replace it with a list of references to other risk assessment standards in lieu of defining one. It was rejected but no explanation was given. Frankly I can think of one. I didn't really submit a true alternative which was a workable solution but essentially substituted one vague answer for another one.

Annex F fails on several major counts. First, timeliness. Annex F doesn't document it but near as I can tell, it is derived from ANSI B11.TR3. This is a risk assessment procedure for mechanical, moving equipment. It is intended for use in analyzing events like assembly lines, hydraulic presses, and automated tools. The event that we are trying to analyze has "exposure" rates measured sometimes in years (between maintenance activities) and where likelihood of failure is measured in 10's of thousands of years.

Second, vagueness. Please explain what "likely", "remote", etc., means in concrete terms? As humans we can generally do a fairly good job of analyzing events with frequencies such as hourly, daily, weekly, etc. But research has shown that we fail to do an adequate analysis of events that occur only every century or every eon without resorting to some kind of mathematical framework. We need concrete definitions here or my definition of "likely" and yours may differ by a wide margin, several orders of magnitude. Similar problems exist with therms like "mild" and "severe" for injuries. This is one of the reasons that I can tell it's just a restatement of ANSI B11.TR3...because the same vague, useless, undefined terms exist in both standards.

Third, it has 4 factors that are assigned values but does not detail what to do with the four factors (add? subtratc? Multiply?). The actual risk assessment is missing here.

Fourth, there is no definition of acceptance criteria. It ends with a simple statement that this is site specific. This is also true of most other standards. Exceptions are CCPS LOPA, PMMI, and ANSI RIA.

Thus we have a "standard" that is not appropriate in terms of time for analysis of electrical hazards, is so vague that we can't define any of the values required, doesn't tell us what to do with those values, and doesn't define what a "good" result is. It is totally ambiguous.


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 Post subject: Re: Types of Risk
PostPosted: Tue Mar 17, 2015 11:51 am 

Joined: Tue Mar 17, 2015 11:22 am
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I even submitted a request to simply delete it and replace it with a list of references to other risk assessment standards in lieu of defining one. It was rejected but no explanation was given. Frankly I can think of one. I didn't really submit a true alternative which was a workable solution but essentially substituted one vague answer for another one?


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