UKTC Archive

Re: Tree Risk Communication

Subject: Re: Tree Risk Communication
From: Jerry Ross
Date: Jul 31 2020 11:36:05
David, Chris got there some years ago with this:

Chris Hastie, arboriculturist and webmaster of the The UK Tree Care Mailing List recently got fed up with the assumptions that are made about such things. He writes:

"After the storms the other month I was phoned by a journalist who questioned me about various things, mostly to do with a very large horse chestnut by the side of a busy road which managed to blow over and do no harm to anything except a lamp post. Trying to explain the nuances of risk management to her and knowing everything I said was going to be massively dumbed down, I started to wish I had a few soundbites at my fingertips.

So Chris took the question at face value and worked out some statistics. He started by pointing out that the chances of being killed by a tree in a public space in the UK is about 1 in 20,000,000 (according to the UK Health & Safety Executive, “Management of the risk from falling trees – Internal guidance”). So, what about winning the lottery jackpot? Actually, Chris also demonstrated that rather than the 14 million to one which is usually quoted, the chances of winning it are actually better expressed as 1 in 268,920. This is because although the chances of winning with one ticket are indeed 1 in 13,983,816, accidental deaths are usually expressed as the chances of any incident happening to any person in one year. So, assuming a lottery player buys one ticket per week every week for a year, the odds are reduced to 1 in 268,920. Thus a regular lottery player is 75 times more likely to win the lottery jackpot than be killed by a tree in a public space. He goes on with some other sobering illustrations. The total number of accidental deaths in the UK is over 12,000 per year. About 6 of these are due to trees. So you are 2000 times more likely to die from some other type of accident than by being hit by a falling tree. More specifically, 3,501 people were killed in road traffic accidents in the UK in 2005. So you are around 600 times more likely to be killed in a road accident than by a falling tree. The Ranger adds one of his own – the annual risk of being struck (and not necessarily killed) by lightning is 1 in 10,000,000. So you are more likely to be hit by a bolt of lightning than killed by a falling tree. That seems to put things into perspective. Anyone else want to have a try? Cite your sources if you do!

Taken from https://naturenet.net/blogs/2007/02/19/killed-by-a-falling-tree-what-are-the-chances/
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Nick Hellis has similarly relevant statistics on his website (or had - I can't locate it now but his website is here https://www.hellis.biz/advice-centre/general/)

The most up to date research shows that between January 1999 and January 2009 there were 64 fatalities in the UK resulting from trees or parts of trees failing an average of 6.4 fatalities per year.

Accidents at work account for 144 fatalities a year and accidents at home account for 3,380 fatalities a year. In other words, you are 50 times more likely to be fatally injured at home than you are to be fatally injured by a tree.

*Non-Fatal injuries caused by Trees*

The number of A&E cases in the UK attributable to being struck by trees or parts of trees is around 55 a year out of a total of some 2.9 million annual leisure-related A&E cases.

Footballs account for 262,000 cases per year;
Children’s swings account for 10,900 per year and
Wheelie bins account for 2,200 cases per year.

*Risk of Fatal Injury caused by Trees*

The annual risk to any one individual of being killed by a tree is 1:10,000,000 (i.e. 6 deaths per 60 million head of population)

The HSE state that people regard a risk of ‘one death in a million’ as insignificant or trivial in their ‘daily or normal life’.

The individual risk of death caused by trees is one tenth or ten times lower than the risk people accept as being insignificant or trivial in their ‘daily or normal life’.

*Fatalities in ‘normal or daily life’*

The following table compares the calculated risks that are experienced in ‘daily or normal life’.

*Causes of death *

        

*Annual risk *

        

*Annual number of fatalities*

Accidents at home, all ages (1)

        

1 in 17,000

        

3,380

Road traffic accidents (2)

        

1 in 37,000

        

1,713

Murder (3)

        

1 in 91,000

        

726

Accidents at work (4)

        

1 in 458,000

        

144

Insignificant or trivial risk (HSE definition)

        

1 in 1,000,000

        

n/a

Trees (5)

        

1 in 10,000,000

        

6.5

Lightning (6)

        

1 in 33,000,000

        

2

Sources:

(1)Office for National Statistics Mortality Statistics – Injury and poisoning

(2)Department for Transport Road Casualties Great Britain: 2013

(3)Year ending March 2018 – Office for National Statistics

(4)Health and Safety Executive – Fatal Injuries in Great Britain 2017/18

(5)Centre for Decision Analysis and Risk Management

(6)Lightning deaths in the United Kingdom: a 30-year analysis…. D. M. Elsom

--------------------------------
However, as Michael suggests, I doubt if knowing all this would stop people asking to have trees taken down 'because they might blow down'.

On 31/07/2020 10:41, David Evans wrote:
Those of you who have to explain tree risk to civilians might find this
useful.

You're at greater risk from going on a 200 miles round trip in a car to
visit friends for a weekend than from branches or trees falling over a whole
year.*

I think this is such a relatable comparative risk that everyone accepts
without thought, and usually involves driving past trees, I'm using it in
the next version of VALID's Tree Risk-Benefit Management Strategies that I'm
working on.

*A micromort is a one in a million chance of death

The risk from a 200 miles road trip = 1 micromort

The annual risk from trees = less than 1 micromort

For those of you who are interested in this kind of stuff.  The 200 miles
statistic is from Tim Harford's marvellous 'Cautionary Tales - The
Spreadsheet of Life and Death', available here.

https://tinyurl.com/y87728p7

It's about why the Value of Statistical Life is so important.  The tragic
tale of Clive Stone is a neat illustration of the folly of not using a VSOL,
and a great skewering of populist politics.  Concerning trees, it explains
why the costs of tree risk assessment and management are a crucial part of
the risk equation.  And why the, 'If it saves one life' argument is an empty
one.

Cheers

Acer Ventura








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