Chris,
As I understood it there is an average of 6 people (non-arbs) a year killed
by trees in the UK, of which HSE reckon that 3 are on private ground and 3
on public ground.
If we assume the UK pop at 60 million (the government has no idea) then the
risk of death is 1 in 10 million.
One can argue that the risk is 1 in 20 million in each instance but not
overall.
Still remote I grant you!
The whole subject of risks from trees must never lose the sense of
proportionality: the balance of appropriate levels of action to the risks
presented.
Jim
-----Original Message-----
From: Chris Hastie [mailto:Chris.Hastie@xxxxxxxxxx.gov.uk]
Sent: 01 May 2008 13:34
To: UK Tree Care
Subject: Risk management - looking for common ground
Risk management is an important focus of the industry at the moment, and
a controversial one. I thought it might be useful to try and draw out
what is common ground on the subject. Here's my starter for ten. I've
also added the beginning of a list of things we just don't know but
probably should.
Feel free to add to the list, but bear in mind that what I'm trying to
do here is to draw out from amongst all the strongly held and differing
views on the subject of risk management those things that we can all (or
at least nearly all) actually agree on.
Common ground
=============
Three parts to tree risk
------------------------
The concept that tree risk is composed of three basic component parts is
common to most notable authors on the subject.
Matheny and Clarke's work is based on this assumption, Lonsdale has
described a similar three factors and Ellison's QTRA deals with three
factors. Although using slightly different terms for the three
components, all these authors essentially identify the same three:
* The probability of the tree, or part thereof, failing
* The probability of there being something there to be hit if it
does fail
* The probability of damage happening, or the severity of damage,
if the tree fails and hits something - often related to the size
of the part that fails.
The risk from trees is low
--------------------------
Perhaps not entirely common ground, but certainly something stated with
some authority in the form of the HSE's Sector Information Minute on
managing tree risk. The annual risk of death per person from trees in
the UK is estimated to be in the region of 1 in 20 million, which is
described by the HSE as "firmly in the 'broadly acceptable'" region.
Owners owe the public a duty of care
------------------------------------
Everyone seems agreed that owners of trees owe a duty of care to the
public. It is the extent of that duty which is contested.
Take more care where there are more public
------------------------------------------
There seems to be fairly widespread acceptance that the higher the level
of occupation of a site, the more effort needs to be put into managing
risk. Trees in the middle of nowhere require less care than those by the
sides of busy roads. What constitutes a high use site is, however,
subject to some disagreement.
Things we don't know
====================
The whole value of tree damage
------------------------------
Thanks largely to JFL's efforts in scouring the media we have a
reasonable idea of how many fatalities there are in the average year as
a result of tree failure.
What we don't seem to have good information on is the total value of
other damage connected with trees. How many people suffer non-fatal
injuries as a result of tree failure? How many cars are dented or roofs
smashed? These data contribute to the total risks from tree failure and
would be useful in defining a proportionate risk management protocol.
How many trees don't fail
-------------------------
Lot's of people spend a lot of time looking at trees that fail.
Collaborative efforts exist to collect data on trees that fail. What we
don't have much idea of is just how many trees don't fail.
--
Chris Hastie
Find a tree surgeon at
http://www.findtreesurgeons.com/
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