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Hi Robin and others Still nothing from Highways, so in the meantime here's how I marked my T values. The vehicular ones are estimates from what I would expect, but I am mindful that things might be different on the ground. QTRA Ruff Wood Walkover.doc Treating this exercise like it was a proper instruction, I contacted West Lancashire Borough Council (WLBC) Countryside Rangers to find out whether they might have some insight into how the wood is managed. Also to find out whether they are given any basic tree hazard recognition training. And out of courtesy to let them know what we’re up to on here, in case they hear about it, stray across it, or have a member of the public express concern. However, I couldn’t get to the person I needed to talk to. It also appears that WLBC don’t have a Tree Risk Management Plan or Policy, like this; http://www.n-somerset.gov.uk/NR/rdonlyres/CCA983EC-0291-4B9B-B2E7-8891E0042D02/0/Mar2012reviewNSCTreeRiskManagementPlanADOPTEDFebruary2011.pdf So, those of you who are having a go with this, how close were you? Any questions about the T values? Based on the T values, any thoughts about where you might expect the highest potential risk to be? Cheers Acer ventura

Hi Simon Almost everyone who plays the lottery loses it nearly all time. The risk of wining it is so low, it's even less than being killed by a tree, at around at 1/14,000,000. David Lonsdale used QTRA, as the defendant’s expert in Harry Bowen and Others v National Trust, in a failed claim for negligence brought against the National Trust, where one child was killed and three others badly injured. I believe he also used elements of QTRA in relation to Target valuation and tolerable risk in an unreported case, before QTRA was published and registered users were trained. If the risk is unacceptable then there are a number of options. It might be possible to manage the target to reduce the risk. Or some pruning may also reduce the risk. Or if the tree is particularly valuable' date=' a case might be made to manage the risk to within a higher band of tolerability 1/1,000 – 1/10,000. Finally, the most suitable form of risk mitigation might be to fell the tree. What is especially useful with QTRA is that you can work out which component to manage, and by how much, in order to achieve a tolerable level of risk. Moreover, because risk is quantified, if a survey reveals a bunch of trees with an unacceptable level of risk, and the tree owner has a limited budget, it’s really clear which tree has the highest risk and needs dealing with first; and so on. QTRA was controversially used in the ‘Poll’ case, where both experts ended up misleading the court as to the level of risk from the tree. They put the wrong inputs into QTRA and came out with a much higher level of risk. Unfortunately, as both experts made the mistake together in a joint statement that said the risk from the tree was high, rather than medium, the court was none the wiser. An additional advantage of using QTRA is that you can see whether a component of the risk might have been 'massaged' to get the result the client wants, and challenge it. Cheers Acer ventura

Hi Rob, and anyone else who wants to have go (whether you want to do it in privacy behind drawn curtains, or chip in) As you’ve probably already seen, I ended up running a worked QTRA example this weekend, which might have helped, but here’s your Ruff Wood one from scratch. How about approaching this as though we were instructed by West Lancashire Borough Council to assess tree risk in Ruff Wood? For educational purposes I’ve snipped a bit off google maps showing Ruff Wood and pasted it into a word document, which I've attached, because I figured this would be the easiest to add text boxes to and annotate. QTRA Ruff Wood Walkover.doc The site can be virtually assessed for Target values from google maps, including street view, and what you might be able to tell us knowing how the site is used. Ruff Lane, Ormskirk - Google Maps With QTRA, the most cost-effective way of approaching this instruction would be to undertake a ‘Walkover Survey’. I’ll explain more about the details of this process as we go through it, but firstly we would treat the woodland as one compartment (in this case W1). The next part of the tree risk assessment is the most important and that is assessing the Target values. So, have a look at table 1 on page 5 of the QTRA PN and have a go at ranking the Targets in relation to the woodland within one of the six ranges. What you’ll end up with is a painting by numbers picture of the Targets adjacent to the wood, and within it. In relation to traffic counts, you might find this site useful. Traffic counts - Transport statistics - Department for Transport If it does occur to anyone to do so, please don’t ring up Lancashire County Council Highways Department to find out whether they have a traffic count for Ruff Lane. I've already done this and they are going to get back to me. I'll let you know when I find out. Have a look, give it a go, and fire away with any questions you have. Cheers Acer ventura

Hi Jonny Wow! I mean really, Wow! Cheers Acer ventura

Hi Jonny Just so I’ve got this right. What you’re saying here is you’ve been wasting my time, and anyone else’s who is following this thread, by feigning ignorance and asking questions to which you already know the answer, and then pretending you don't understand my replies? Cheers Acer ventura

Hi Jonny We seem to be posting at exactly the same time today. It's not just the chances of a tree/branch hitting the car though, it's also the chances of the car hitting the tree/branch if it falls into their path as well. It's both. That's what would be the contact area. I linked this in an earlier post as a pdf, but have converted it to a picture.

Hi btggaz Here’s the worked example I promised earlier. Target (T) - We always start with the T because it’s the most important part of the risk calculation. If we allow for at least one car journey there and back for each of the 20 odd houses every day of the year, and some more to allow for visitors and additional trips and suggest 65 car journeys/day, which is corroborated as reasonable by those who now the site better, we end up with the highest value in T, Range 4. Impact Potential (IP) - Let’s go to the upper end of your estimate of branch diameter 400-500mm, so IP is in Range 1. Probability of Failure (PoF) - Now we have T and IP, we can move the inner PoF component around to see how ‘fecked’ the branch has to be before we get an unacceptable level of risk. If the PoF is in Range 3, 1/100 – 1/900, which is a high PoF, the RoH = 1/70,000 (Risk Index 70). The current manual calculator doesn’t have PoF Range 2, 1/10 – 1/90 on it because we didn’t have the space, but it’s easy to work out. A PoF Range 2, 1/10 – 1/90 is x10 higher than Range 3 because it’s the highest value in the range that we input. 10 is a x10 higher PoF than 100. Therefore, because the PoF is x 10 higher the RoH is x10 higher. Back to the calculation. If the PoF Range is 2 then RoH = 1/7,000 (70,000/10), which would be regarded as an unacceptable level of risk. What all this means is that from knowing the T and IP we can work out the branch has to have a PoF in Range 2 before the risk becomes unacceptable. For a branch of 400-500mm to have such a high PoF it would have to remarkably defective and be displaying incipient indications of failure with no significant adaptive growth. This is a very straight forward skill after training because all you’re doing it aligning the components on the manual calculator. It’s much easier to talk through in the workshop, and do in the field than write out on here. All it takes is a bit of detective work to put in credible T values based on those who know the site. Now if these are posh houses with two cars and we expect more than 65 car journeys/day, with the manual calculator we would move up to the next T range. With the software calculator we’re not constrained by the size of the manual calculator and have more space, and we could look to refine with say 100 vehicles/day, and see the RoH for the same branch with a PoF Range 3 is 1/50,000. Cheers Acer ventura

Hi Jonny How very dare you. I am trying to answer the questions, time permitting, in the order in which I get them. I'll queue jump you because it's an easier answer than getting onto WorcsWuss's calculation of bending moments. However, though it's great that you're interested and are asking questions, I really recommend you take the time to have a look at the PN because it may contain the answers to your questions, and if it does it would help with the backlog on here. 30mph is not half the time of 60mph because of stopping distances. We don’t try to reduce the likelihood of a fatality based on speed. A car driving at 100kph has an occupancy time of 3.95 seconds. A car driving at 50kph has an occupancy time of 1.85. If there is 1/1 Impact Potential within these time frames then the consequences are calculated as a fatality for both speeds. Even if the failure is in the 50kph zone and the branch/stem falls onto the road at the outermost extent of the stopping distance, so by the time the car hits it it’s almost stopped. In other words there’s a considerable safety margin built in because we’re calculating on the worst outcome. Is that what you were getting at? Cheers Acer ventura

Hi btggaz Glad to hear you’ve found the thread interesting, and you’ve raised some really profound stuff with your posting. So please bear with me whilst I explore the issues with you. I think a particularly important benefit of quantifying tree risk, so we can relate it to a published level of tolerable or acceptable risk, is that the ‘moral’ side of societal risk, at 1/10,000 and 1/1,000,000, has been decided by higher authorities and experts whose specialist field is risk management. If you think about it, if we don’t’ quantify risk relative to a published threshold we are taking a ‘moral’ decision into our own hands. We’re playing god, and deciding a level of risk from a tree which could kill someone, and worse still we’re not sure what that level of risk is. I think this is one of the reasons why arboriculturists are understandably hard-wired to be risk averse rather than risk aware, because the last thing we want to happen is that someone could possibly die from the failure of a tree we’ve assessed or worked on, irrespective of the level of risk. So naturally, we habitually look at what could happen, rather than what is likely to happen.

Hi Jonny I'm just sorting out a worked example for btggaz, but popped into answer you becasue it's an easier question. I would recommend starting at the beginning of the thread. Break it up into small sessions. You may even find the PN, which answers your questions. In short 1 occupied car = 1 life. Whether the car cannot stop in time before hitting the tree/branch and/or if the tree/branch hits the car. If you can't find the PN, you could always try this. Let me google that for you Cheers Acer ventura

I couldn't agree more Jonny. No one want's to see premature quantification. Cheers Acer ventura

Hi Jules Sorry to hear you had a bad day. I’m very happy to keep the thread on topic with QTRA Q&A and for you to keep your methods covered up. However, if you’re going to expose your methods, like you did earlier, and as you are again above, and I would like some clarification on them, think there’s a shortcoming in them, or even that they’re a good idea, then I think it only reasonable and fair that I comment on them. So, on this occasion I'll not seek further clarification on what looks an unusual take on ALARP principles. I beg to differ. I think the PN clearly shows the nuts and bolts. It’s 8 pages long and shows what’s in QTRA and how it’s put together. Its purpose is to inform the client of what the QTRA assessor is doing and why' date=' and we recommend the PN is included in the appendix of any QTRA reports. What it doesn’t do, and isn’t supposed to, is tell the reader how to use QTRA. If we go back to the car analogy, the PN is a very detailed but extremely dull brochure. The 34 page User Manual, supporting PowerPoint presentation, private Registered User’s Discussion Forum, the day’s training, along with the recommended but optional VTA day to expand further on the PoF element, are what will help the assessor drive QTRA. Just to clarify, you can’t get a 1/5 and 1/50 PoF using QTRA. Cheers Acer ventura

Is that near Mordor? Congratulations with your assignment score, you square. I think it would be best to go for your woodland. There’s a potential can of worms in your assignment that it would be better not open and have wriggle all over this thread. As an aside, was it your lecturer who suggested using the Matheny & Clark Hazard Evaluation Form and Rating? Shall we start here Ruff Lane, Ormskirk - Google Maps Bing Maps - Ruff Lane, Ormskirk Cheers Acer ventura

Goode Judgment I've had a quite a few comments about this off-forum since coming on to Arbtalk, others have raised it with me in the past, and Robin led with it in his QTRA thread before Christmas. It seems that some are claiming the Goode Judgment is a legal silver bullet to the big bad QTRA werewolf. In my first post in this thread I attached a reply from Mike Ellison that covers some serious concerns about the reasoning behind the judgment, and raised the remarkable contradiction with the Commissioner criticising the implied precision in the QTRA calculation, and then adapting and misusing the QTRA calculation to claim the risk was unacceptable. I would urge anyone who's had the Goode Judgment waived at them to have a look at Mike's comments. What I want to briefly do here is dispel what appear to be some common misconceptions around it that have been brought to my attention, and make a quick additional point about subjectivity in the judgment. Though the words 'court' and 'judgment' are used, it's worth noting it's the judgment of a 'Commissioner'. This is an important clue to its status because Goode is not a High Court case. The best analogy is that it's an Australian equivalent of a 'planning appeal' resulting from a refusal to fell a protected tree. It does not set any legal precedent. I have already dealt with the implied precision issue, and expanded on subjectivity v objectivity early in this thread. The comment about the 'subjectivity' in QTRA is a theme that I'm told recurs when Goode is raised. If you read the judgment you'll see appellant's expert's (Mr Nicolle) risk assessment is that he looked at the trees, their branches, and garden beneath it and concluded the risk is 'moderate', and that a 'moderate' risk is an unacceptable risk. In terms of a risk assessment, and a determination of whether a risk is tolerable or acceptable, I'm not sure it's possible to be any more subjective. Nonetheless, this is the evidence Commissioner Hodgson preferred. Notwithstanding the entirely subjective nature of Mr Nicolle’s risk assessment that he was able to convince the Commissioner a moderate risk is an unacceptable risk is rather concerning. Cheers Acer ventura

As there’s suddenly been an increase in traffic on this thread and questions raised, I thought I should point out that I could take some time to reply, and I may soon have to abandon it for a month if it’s not run its course by then. Like you all, I have proper work to do but with some particularly pressing deadlines because at the end of the month I’m running a QTRA workshop in London, and then heading off to Australia to run QTRA, VTA, and QTRA Update workshops over there over 3 consecutive weeks. Besides that, once over there I’m led to believe those ice cold beers won’t drink themselves. In the meantime, I’m going to try and reply to messages in the chronology they were posted. So if you’ve asked something and you’re wondering why I haven’t replied yet, I’m not ignoring you. Cheers Acer ventura

Hi WorcsWuss Interested bystander's points of view are very welcome. Unfortunately, trees aren’t like floor beams though. In terms of risk assessment it would be brilliant, because they could actually be far more accurately ‘quantified’ in the same way that buildings are structurally designed. The trees might not be quite so interesting though. Trees are both anisotropic and generating systems growing a new layer of wood every year. They have the capacity to self-optimise and preferentially lay down more of the new wood, with improved structural quality, where there is increased mechanical loading, and lay down less wood where there is reduced mechanical loading. It’s their ability to do this that can give them a body language we can begin to interpret with Visual Tree Assessment. Additionally, their ability to resist decay is partially down to their vitality, which not only determines how quickly they can lay down new wood in response to increased movement from decay, but affects their capacity to maintain functional wood, which is generally an inhospitable environment to many decay fungi. All of which are some of the reasons why PoF is a judgement call within a broad range, and a reason why strength-loss formulae are so limited. It's the component we are most uncertain about with present knowledge.

Hi Jonny It’s a good preference, and QTRA works in broad ranges. I don’t know whether you’ve had the stamina to go through all the thread but it’s a key element to what we were discussing starting from around post 24. Sometimes we can refine the Target if better and credible information is available from an authorative source because some of those ranges are so broad, but only if otherwise the risk might be unacceptable because we’re using broader ranges and calculating from the highest value. BTW David Lonsdale is happy to refine elements of QTRA beyond the broad ranges. He did this in his ‘Felbrigg’ expert witness report. Cheers Acer ventura

Hi Robin Your first question goes back to the first couple of posts in the thread. Did we really manage it well enough before? I don’t think we did, and I don't think we do now – though things are changing. If we don’t quantify risk then there is a natural and hard-wired tendency to be risk averse, which results in wasted resources where more money and time is spent assessing trees for risk than is necessary. And trees, branches, and associated habitat can be unnecessarily removed because they are regarded as having too high a risk. I think this is mainly down to the difficulty risk managers and risk assessor's have without a tolerable or acceptable level of risk to measure against. Otherwise, how do you work out whether the the tree/branch is safe or not? - Particularly if it could be regarded as defective. A common theme that is apparent amongst those that come out of the other end of QTRA training is they spend less time assessing tree risk than they used to before. They can assess more trees within the same period of time than before. Their assessments also generate a less tree work, and they feel more comfortable about their position if a risk were to be realised. However, those that benefit most from quantifying tree risk are the managers and tree owners. Hopefully, I will be co-presenting a paper with John Flannigan at the AA conference this year that covers part of this. North Somerset Council were one of the first Local Government Agencies to adopt the principles behind QTRA as policy in their Tree Risk Management Plan. The beneficial consequences of this are many fold. Not least because they now spend less money assessing tree risk, less money felling trees, and therefore retain more tree-related benefits. Saved money they can now spend on the likes of establishment and formative pruning. An important and additional spin off is in the event of a risk being realised. If that risk was less than 1/10,000 they are in a very robust position to defend a claim against them, and fend off the HSE possibly serving an Improvement Notice, which could leave them vulnerable to civil claims. Part of what I hope to be covering is a case where this happened in the car park in one of their woodlands. Because the risk was 1/400,000 they were able to politely refuse to pay out on claims from the car insurance companies for the four cars that were written off because the risk was tolerable.

Hi Jules I’m very sorry you hear you feel that way. This is a discussion forum, and you did ask me what I thought about DIY tree risk quantification, and then embellished the notion with an example of how you go about it when assessing human targets. You also indicated you would be willing to discuss the risk assessment of this scenario but with a hypothetical tree using your method, which I still know little about. I have tried to answer you and discuss the issues you’ve raised in a polite and neutral manner and keep the subject matter about the facts. On this thread I have been happy to respond to any criticism levelled at how QTRA goes about risk assessment. Dissection is a good thing. The way I figure it, if QTRA has merit then it will stand up to open scrutiny. If the wisdom of the crowds highlight areas where it could be improved, and their point is well founded, then it would be unwise not to take these on-board and improve the system. One of the driving forces to how QTRA has evolved is the feedback and opinions from the hundreds of registered users from around the world both during the training and when they start to apply it. And yes, even from discussions on forums. Cheers Acer ventura

Hi Jules I think there’s two fundamental issues here. Firstly. In pursuit of the published 1/10,000 and 1/1,000,000 thresholds, sure, you can have a SWAG (Scientific Wild Ass Guess) at pedestrian Targets knowing there are 86,400 seconds in a day and 8,760 hours in a year with some basic maths, which is great. But how would you go about quantifying the road use, or putting a value on a structure like a parked car relative to human occupancy? And what about the other components of a quantified risk. How are you quantifying the Impact Potential (Size of Part), and the Probability of Failure? Notwithstanding the ALARP calculation. The second one being. As well-intentioned as your efforts to quantify risk are, how do you think your personal take on quantification would stand up in court to the forensic scrutiny and cross-examination from a barrister in the unfortunate event of a risk being realised? One considerable advantage of buying into a system is not just the pedigree and credibility of the system, but if you follow the guidelines of a tried and tested system, then as a risk assessor you enjoy a substantial amount of protection, as does the tree owner. The tree owner, more importantly, is generally the duty holder who holds the liability that would be especially vulnerable to any claim for compensation in such an event; not least because their pockets are likely to be deeper. Cheers Acer ventura

Hi Jules Okay then but it’s a shame. I was rather hoping by breaking this particular tree risk assessment down into easy to digest bite size nibbles, we might be able to address some of the points from your messages and apply other ones that have been raised in the thread. Nonetheless, there’s a couple of rich seams I think we could selectively mine without going all open cast on it. These nuggets regularly crops up in the QTRA workshops as well.

Hi Jules How are you working out whether a tolerable risk is ALARP? You are the black box with this system.

Hi Jules Thanks for chipping in, and good to hear you get the value of quantifying tree risk. You may particularly enjoy the quote at the head of the QTRA Practice Note. "When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind” William Thomson, Lord Kelvin, Popular Lectures and Addresses [1891-1894] On the contrary' date=' there’s nothing at all [b']‘black box’ [/b]about QTRA. Just the opposite is the case. Absolutely everything about how each component is derived, and how the risk is calculated, is transparently laid out in great detail in the Practice Note (you don’t need to be a registered user to see this) and User Manual. There’s a link to it in my reply to Robin. Of the free systems that are available, I don’t know of any that aren’t built on ‘black boxes’ and 'mysterious processes' in that the hows and whys of the components of the risk are not disclosed. They just are. Or where a level of acceptable risk is suggested, the basis for it is not disclosed; ie it’s little more than the opinion of the person that put it together.

Hi Robin I think you meant 'risk' rather than 'hazard', but for anyone who might be following this and isn't sure of the distinction, and so we're singing from the same hymn sheet. Hazard “A hazard is the disposition of a thing, a condition or a situation to produce injury.” (HSE) Risk The probability of something adverse happening. Every tree is hazardous to some extent, and extremely hazardous trees can have tolerable or acceptable levels of risk. As an aside, hazards can have substantial ecological value. Something that’s really promoted on this site from those interested in veteran trees. I think it was David Lonsdale who was telling me that the Forestry Commission’s ‘Recognition of Hazardous Trees' leaflet was withdrawn because of its similarity to the ideal veteran tree (Veteran Trees: A Guide to Good Management). The first part of the answer is in my first post on the thread' date=' and here's one I made earlier. Why Use QTRA.pdf Cheers Acer ventura

Hi Robin There's no time constraints on exchanges here. In these days of instant communication it's all too easy to let the fingers reply to a message before the brain has had a chance to intervene. Taking the time to have a think about something is a good thing. I didn't pick this bit up in the email alert, and I see you've edited to add it, so I'll get back to you on it later (depending on how refreshed I get during the Ireland v England game this afternoon). However, there's one point I can make straight away. QTRA is a risk assessment, not a hazard assessment. This isn't semantic pedantry, it's a really important distinction. As a teaser, if you quantify risk with QTRA, determining whether a risk that falls within the ToR Framework Tolerable Region between 1/10,000 - 1/1,000,000 is ALARP is very straight forward. Cheers Acer ventura