Quantified Tree Risk Assessment (QTRA) - Questions & Answers

[Acer ventura]

I like to think of Kenwood gate on the heath for a great example, a funnel for millions of people per annum.

 

Hi Tony

 

Where is this? How many people/hour funnel through there when you have wind gusts hitting gale force 8 (39–46 mph 34–40 knot)? Say you have Gale force 7 - "Effort needed to walk against the wind", and gusts hitting Gale force 8, "Progress on foot is seriously impeded". 40 knots is when you start to get branch failure. That's the pedestrain occupency you would put into the Target.

 

I do think this inherently low risk generally from trees is always going to be a thorny issue.

 

It's not thorny' date=' it's really important because it informs 'proportionality'.

 

I would be very interested in your views on "the limitations of strength loss formula"

 

A subject for another thread. Perhaps when this one has run its course.

 

Cheers

 

Acer ventura

[Tony Croft aka hamadryad]

Hi Tony

 

Where is this? How many people/hour funnel through there when you have wind gusts hitting gale force 8 (39–46 mph 34–40 knot)? Say you have Gale force 7 - "Effort needed to walk against the wind", and gusts hitting Gale force 8, "Progress on foot is seriously impeded". 40 knots is when you start to get branch failure. That's the pedestrain occupency you would put into the Target.

 

 

Cheers

 

Acer ventura

 

Its the gate between the grounds of kenwood House and Hampstead heath, its on David Humphries watch so maybe he will jump in with a discussion on his take of risk managment as a non QTRA practitioner?

 

I think its said to have 7 million through its gates annualy. I just like it as a measure because it has one of the highest throughput's of uman footfalls that I know off and has many large and old trees on route

[Gary Prentice]

As RobArb said, this is quite difficult to get your head around at times, but thanks for expanding on some of the issues. Like anything else, regular usuage, would expand the understanding.

[Tony Croft aka hamadryad]

As RobArb said, this is quite difficult to get your head around at times, but thanks for expanding on some of the issues. Like anything else, regular usuage, would expand the understanding.

 

Agreed, planning on getting this under my belt as soon as poss, dont know till you know if you know what I mean!

[Acer ventura]

I do understand the points you are putting across, my learning pathway though tends to question anything i don't fully understand until i do fully understand it. I have been told that this is both a good and bad way to learn:biggrin:

 

I fully appreciate the time and effort you are putting into the replies here and your explanations are clear enough to me and please don't take my argumentative questionings any other way than a desire and curiosity to learn:thumbup1:

 

Hi Rob

 

Thanks for the appreciation and I’ve been happy to try and answer your and Tony’s questions. I take the position there’s no such thing as dumb or bad question, and one of the things I think is really important when running both the QTRA and VTA workshops is ensuring that everyone is comfortable so they don’t hold back. I wanted to do that on here as well.

 

I’m very mindful QTRA can initially mess with arborists heads because it may seem contrary to what they have been brought up with and what they learned in college. An arborist called Dom Scanlon phrased it very nicely after he did the training and said he had to ‘unlearn’ what he had learned at college in order to get his head around it. Something I can sympathise with because I was at the same college with him.

 

I think one of the main reasons for this ‘cognitive dissonance’ is because QTRA is founded on the principles of ‘risk’ and ‘probability’, which apply to any field, rather than having a look at defects or hazards in a tree. Hence the opening post on this thread was about what risk is, and what a tolerable or acceptable level of risk was. It’s interesting that on training seminars and during presentations non-arborists can often ‘get’ QTRA before arborists do. Dom also told me a tale about when he was explaining to a potential client, who was an engineer, how he assessed tree risk with QTRA and showed him the manual calculator (the wheel). Whereupon the engineer got something very similar out that he used in his profession. Needless to say, there was little effort required in persuading them in the merits of quantifying risk.

 

The maths and probability side of risk is also new to many, but a lot of that is by way of understanding why QTRA does what it does. All the assessor has to do is work out the Target value in a broad range first, which is the bit they know the least about and may require a bit of work asking their client or talking to highways, and then the arborist can get onto their favourite bit of looking at trees.

 

I'm sure QTRA has its place otherwise it wouldn't exist in the way that it does now' date=' but until it is possibly part of my day to day work life there's just something that "doesn't fit" and i can't thoroughly explain why?

 

I have been known to turn though:biggrin:[/quote']

 

Understanding QTRA can take a while when you first read about it, or hear about it second-hand and get inaccurate information or misconceptions, and you don’t have the benefit of the interaction and application you get on a training workshop. Next time you’re pruning a tree within falling distance of a road have a think about how you would work out the risk. Think about what an acceptable level of risk is, and with a road Target ponder how much more valuable it is knowing the likelihood of occupation as a probability, then it is to try and make sense of ‘a lot of cars’, ‘some cars’, ‘is it different during rush hour’, ‘blimey that Lamborghini was a horrible colour’.

 

Jim Quaife passed on a great quote he heard on a programme from Professor Sir Roger Penrose. “To have one’s mind changed is exhilarating!”

 

Cheers

 

Acer ventura

[Acer ventura]

On the RobArb QTRA thread that gave birth to this one, a gentleman by the name of showoffsummer raised Julian Forbes-Laird’s (Claimant's expert witness) - 'Supplementary Report on QTRA' from the Bowen & Others v National Trust court case (8).

 

http://arbtalk.co.uk/forum/general-chat/50770-qtra-im-sorry-i-dont-agree-2.html#post771579

 

You might be interested in David Lonsdale’s response to the ‘Supplementary Report on QTRA’ (9), and how David used QTRA and the Health and Safety Executive's (HSE) Tolerability of Risk (ToR) framework in his expert report (6) when determining whether the risk posed by the tree was tolerable.

 

There’s a whole bunch of files relating to the case which are numbered in chronological order, after the Judgment, which are available through the QTRA website:

 

Quantified Tree Risk Assessment

 

1) The Judgment

2) The Particulars of Claim

3) The Defence

4) The Claimants' arboriculturist expert witness (Julian Forbes-Laird) report

5) Appendices to Julian Forbes-Laird's expert witness report

6) The Defendant's arboriculturist expert witness (Dr David Lonsdale) report

7) The arboriculturist experts' joint statement

8) Julian Forbes-Laird (Claimant's expert witness) - 'Supplementary Report on QTRA'

9) Dr David Lonsdale (Defendant's expert witness) - response to the 'Supplementary Report on QTRA'

10) Dr David Lonsdale’s Commentary on the case

 

Cheers

 

Acer ventura

[RobArb]

I tried to read these (from when they where posted in the earlier thread and i was looking for a counter-argument:blush:) and to be honest, i got lost in all the information

 

Its a big read and Uni work got in the way, will have to come back to it when i have more time:biggrin:

 

It seemed worth a read though:thumbup:

[Acer ventura]

Hi Rob

 

In the context of this thread, just have a read of David Lonsdale's 'Supplementary' at (9). It's not very long but a marvellously detailed forensic dissection and dismissal of the attempted criticism levelled at QTRA, but also addresses some of the questions you have raised on here.

 

Cheers

 

Acer ventura

[RobArb]

Thanks David/Acer, will have a look when I get in:thumbup:

 

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[David Humphries]

Its the gate between the grounds of kenwood House and Hampstead heath, its on David Humphries watch so maybe he will jump in with a discussion on his take of risk managment as a non QTRA practitioner?

 

I think its said to have 7 million through its gates annualy. I just like it as a measure because it has one of the highest throughput's of uman footfalls that I know off and has many large and old trees on route

 

 

 

Appologies Rob/Acer I have nothing to input here regarding the thread, would just like to clarify something.

Tony, ftr it is the entire site of the City of London run Hampstead Heath (approxixmately 600 acres) that has an estimated 7 million annual footfall (based on electronic counters at strategic entrance points), not just the one gate between the two sites of HH & the Kenwood Estate at the Kenwood gate.

 

There are at least 6 shared gates between the two sites and numerous entrance points onto the heath, which is largely open to the public 24/7 unlike Kenwood which gets locked at dusk.

 

 

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