Tree Risk Assessment Qualification (TRAQ) – ISA Best Management Practices

[Acer ventura]

Another question if I may?

 

Are there equivalents in the USA and Australia of the ToR framework? And if not, do you consider it universal enough to be applicable there?

 

Hi Jules

 

There’s plenty. Google Tolerability of Risk Framework, and/or Tolerable risk 1/10 000, with the respective country of interest and take your pick.

 

I often use this in presentations, which some of you might remember from a UKTC thread some years back.

 

 

I followed up the story and found a guy called Nicholas L Johnson, NASA Chief Scientist for Orbital Debris, who I emailed to ask about how they calculated the risk, and what level they managed their risk to. Here’s part of his reply.

 

 

What’s really neat about this is that those agencies who have signed up to the agreement now engineer satellites so that upon re-entry no bit survives is large enough to have a risk greater than 1/10 000. QTRA users are able to apply exactly the same principle when doing walkover surveys when they have the Target Range because by back calculating they can work out which Size and Probability of Failure is required to get a risk higher than 1/10 000, and restrict the assessment to those parts.

 

Something else I found interesting about the news story is it looks like the press release prefixed the 1/3 200 with the word ‘just’ and no one batted an eye-lid because it ‘anchored’ them to the word. Whereas, had it been as ‘high’ as 1/3 200 there may have been more concern because of where it sits in ToR. It's an insight into risk communication.

 

BTW the UARS was launched before the inter-agency agreement. I followed this up awhile back and China and India have also signed up to the 1/10 000 threshold. North Korea, on the other hand...

 

Cheers

 

Acer ventura

[Acer ventura]

Yes, I can, but as someone who's not a registered QTRA user, what's in it for me?

 

Hi James

 

Oh, I don’t know. Sharing your wisdom and insight on the Arbtalk discussion forum for the greater good?

 

Given the subject matter, how many trees could be affected, how much money could be spent on tree risk management, potential loss of tree benefits, and the duty of care issues on the part of the risk assessor and risk manager, I’d of thought the content of this thread would have a much wider audience than QTRA Registered Users. If I thought it was just of interest to them then I’d have posted on the QTRA Discussion List. I did invite contributions to the thread from the QTRA Discussion list, UKTC, and the Linkedin American Society of Consulting Arborists (ASCA) Group.

 

I don't want to be unhelpful when it's a matter of interest to wide range of arbs' date=' or where questions are of a not for profit nature, but I get the impression that what you are trying to achieve here is solely for the monetary benefit of QTRA Ltd.[/quote']

 

Really? I’m aware of your longstanding antipathy towards QTRA, and quantifying risk in general, and I'm sure there’s not a lot I can do about your impression of my alleged lack of integrity.

 

I think I've already covered part of this in my reply to Jules. However, let’s play out your contention. Even if I were paid by my weight in gold for each and every post on this thread by QTRA, what factual difference does that make to the content of the posts in the thread? Are any of the points I’ve raised somehow less valid? Can we try to keep on topic and drop the attempts at defamation?

 

BTW' date=' and as an aside, has this new Monte Carlo method of tree risk assessment been peer reviewed?[/quote']

 

Version 5 of QTRA isn’t a new tree risk assessment method, and it’s not a Monte Carlo method of tree risk assessment, whatever one of those might be. Monte Carlo simulations are now used when calculating the Risk of Harm probabilities. This means the most likely outcome is calculated from a distribution when the Target, Size, and Probability of Failure ranges are inputted. With previous versions of QTRA the highest value of the inputted ranges was the Risk of Harm. Mike hired a mathematician to run the Monte Carlo simulations. If you want more detail about it then contact him direct.

 

You might find it useful to have a look at the Practice Note.

 

Quantified Tree Risk Assessment

 

Cheers

 

Acer ventura

[daltontrees]

Hi Jules

 

I was looking to express what the upper value of a risk ranking of less than <1/2 per annum for a fatality would mean in language outside of probabilities. Another way. Consider there are 30 trees in the school with a Risk BMP ranking of Low risk <1/2 for a fatality per annum. What’s the worst that could happen and the risk ranking still be correct?

 

Does that clarify it?

 

Cheers

 

Acer ventura

 

Yes that clarifies that there is more than one tree. However, isn't the risk of 14 of the trees failing and killing a child each is 1/2 to the power of 14 or 0.000061, following the multiplication theorem of probability?

[daltontrees]

 

I’d be interested to read what you’ve got to say. Any idea of where and when it might be available?

Peer review can take a while, and it's out of my control. It'll come along in due course in one of the Journals.

[daltontrees]

The hazard rating system added ordinal numbers, and the Risk BMP, quite correctly, specifically points out this shouldn’t be done.

 

Well, I,m afraid that I disagree with this, I think Matheny & Clark were way way ahead of the game on this, for reasons that I will be exploring in my article. The latest ISA manifestation seems to misundertsand them, and the outcome is the proabilistic mayhem that you have flagged up in this thread.

[daltontrees]

Thanks. Unfortunately the NASA threshold is 'harm' and th HSE one is 'death', so they are not quite compatible. But I shall have a look elsewhere to establish the reliability.

[daltontrees]

Version 5 of QTRA isn’t a new tree risk assessment method, and it’s not a Monte Carlo method of tree risk assessment, whatever one of those might be. Monte Carlo simulations are now used when calculating the Risk of Harm probabilities. This means the most likely outcome is calculated from a distribution when the Target, Size, and Probability of Failure ranges are inputted. With previous versions of QTRA the highest value of the inputted ranges was the Risk of Harm. Mike hired a mathematician to run the Monte Carlo simulations. If you want more detail about it then contact him direct.

 

 

I have my concerns about the use of Monte Carlo simulations only for QTRA, it is the single biggest turn-off for me of the whole QTRA model.

 

I told Mike what I thought about it at the Conference dinner, but after quite a few drinks maybe I didn't put the point as clearly as I thought I did. Come to think of it, he called me (with a grin) a cheeky b..... but took my point. Or so I thought.

[Acer ventura]

Yes that clarifies that there is more than one tree. However, isn't the risk of 14 of the trees failing and killing a child each is 1/2 to the power of 14 or 0.000061, following the multiplication theorem of probability?

 

Hi Jules

 

Pendant’s hat on - it would be less than <0.000061 for a Low risk rating of less than <1/2 for a fatality. But that would only be the case if you pick the 14 out of the 30 trees that all have an equal Low risk rating of less than <1/2 of failing and causing a fatality, AND then identify the correct sequence in which each one of them fail and cause a fatality over the year. What you’ve done is calculate the odds of picking the correct sequence of heads or tails with 14 consecutive tosses from an unbiased coin.

 

Cheers

 

Acer ventura

[Acer ventura]

Well, I,m afraid that I disagree with this, I think Matheny & Clark were way way ahead of the game on this, for reasons that I will be exploring in my article. The latest ISA manifestation seems to misundertsand them, and the outcome is the proabilistic mayhem that you have flagged up in this thread.

 

Hi Jules

 

Perhaps worthy of another thread?

 

Given Nelda Matheny is one third of the principal authors of the Risk BMP, I think she might disagree with you that’s she’s misunderstood her previous work with Jim Clark.

 

I agree Matheny & Clark were pioneers with their approach in 1994. But that’s 20 years ago and things move on and develop. Moreover, there are some really important caveats in their publication about how their hazard ranking system should be applied which are still frequently ignored. One of the interesting things I’ve found researching tree risk, and running training workshops, is just how many versions of Matheny & Clark’s hazard ranking system are knocking around out there as methods of assessing risk, instead of ranking hazard. Often with additional numbers bolted on to try and massage the end result to reflect a level of risk that the designer thinks the tree should have.

 

Cheers

 

Acer ventura

Edited May 20, 2014 by Acer ventura

[Acer ventura]

Thanks. Unfortunately the NASA threshold is 'harm' and th HSE one is 'death', so they are not quite compatible. But I shall have a look elsewhere to establish the reliability.

 

Hi Jules

 

The 'Risk of Harm' at the top of the slide are my words, not NASA’s which are in quotation marks, because the slide is in the context of a QTRA presentation and that’s how QTRA refers to the risk probability. Nicholas Johnson referred to a ‘human casualty’, which is a euphemism for a fatality. I suspect part of NASA's model is that if someone is unfortunate enough to be hit by a bit of falling satellite they're likely to die. If you look online, at their website and articles about what the Orbital Debris researchers have been looking to achieve, it seems clear the consequences are a fatality.

 

Cheers

 

Acer ventura