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What is a hazard tree


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Some ideas on what might be considered a hazard tree, or not.

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What is a hazard tree

  1. 1. Some ideas . . .Jonathan Hazell26 March 2013
  2. 2. When might a tree be a problem?• “Trees are hazardous when the failure of one or more of their partsresults in property damage and/or personal injury. All trees have thepotential to fail, but only a relatively few actually do so.”• “Tree hazard assessment involves three components:• a tree with the potential to fail• an environment that may contribute to that failure• a person or object that would be injured or damaged (i.e. the target)• “Unless a target is present a tree can not be hazardous.”© Matheny and Clark, Evaluation of hazard trees in urban areas, 1994
  3. 3. When might something be done?• “The most critical questions to answer when making decisions onwhether to inspect trees and whether remedial actions is required are:• Can a problem be foreseen? If so:• What is its likelihood of occurring• What is the likely consequence of its occurrence?• Is it reasonable to protect against it?”© Lonsdale, Hazards from trees: a general guide, 2000
  4. 4. “reasonably practicable” (1)• reasonably practicable, as defined by Judge Asquith in Edwards vNational Coal Board (1949):• Reasonably practicable is a narrower term than physically possible, and seemsto me to imply that computation must be made by the owner in which thequantum of risk is placed on one scale and the sacrifice involved in themeasures necessary for averting the risk (whether in time, money or trouble)is placed in the other, and that, if it be shown that there is a grossdisproportion between them – the risk being insignificant in relation to thesacrifice - the defendants discharge the onus on them.• In other words, if the overall cost of the measures required tominimise the risk of injury grossly outweigh the benefit arising fromthe reduced risk, then no action is necessary
  5. 5. “reasonably practicable” (2)• the Court of Appeal in Leakey v National Trust (date) defined thescope of the duty as• “a duty to do that which is reasonable in all the circumstances, and no morethan what, if anything, is reasonable to prevent or minimise the known risk ofdamage or injury to one’s neighbour or his property”• In his discussion of Leakey Mynors advises• “You are thus only under a duty to protect those who are “reasonably” likelyto be affected by any omission on your part, and only if you can “reasonably”foresee that they are likely to be injured as a result; and even then you areonly required to take reasonable care to avoid such omissions. And MegawL.J. in Leakey only envisaged a duty to do that which is reasonable in allcircumstances.”© Mynors, The Law of Trees, Forests and Hedgerows, 2002
  6. 6. Hazardthe potential to causeharm, be that injury topersons or damage topropertyHSE. 2000: Successful health and safety management, HSG 65
  7. 7. Riskthe likelihood that anundesired event will occurdue to the realisation of ahazardHSE. 2000: Successful health and safety management, HSG 65
  8. 8. Targeta person or object, whethermobile or fixed, within thepotential zone of impact of atree or its branches, whichmight be harmed as a result ofthe partial or total failure of thetreeNOTE: The term can also referto a pedestrian or vehicularroute where harm might thusoccur.BSI. 2010: BS 3998: 2010 Tree work – Recommendations
  9. 9. Is this ahazard tree?“Unless a target is present a tree cannot be hazardous.”Undeniably it has a number ofstructural defects that afford the treethe potential to cause harm, but arethere any targets?
  10. 10. Another view
  11. 11. Is this ahazard tree?There is a track next to thetree, the level of use willdetermine the level of risk totargets and so whether, or not,something might be done:“Can a problem be foreseen? If so• What is its likelihood of occurring• What is the likely consequence of itsoccurrence?• Is it reasonable to protect against it?”
  12. 12. Is this ahazard tree?
  13. 13. Another view
  14. 14. What about this one?
  15. 15. What do you see here?
  16. 16. What do you see here?
  17. 17. Does this help?This is T01 from theprevious slide
  18. 18. Does this help?This is T03 from theprevious slide
  19. 19. What do you seehere?
  20. 20. Or here?