19 Viewland Drive Arborist Report · OPW19/0180

Consult Arborist .....

 

APPENDIX 2 — TREE RISK ASSESSMENT METHODOLOGY

The methodology of rating risk used in this report is based on the following International Society of Arboriculture’s Tree Risk
Assessment and is calculated through the use of qualitative risk matrix tables.

Initially the Likelihood Matrix is used to estimate how likely a failure will be to impact a target. This is calculated by categorising
how likely failure is to occur and combining that with how likely that failure is to impact a target, as per Table 1.

1=- Matrix

   

im;
= to a target

Once the Likelihood of Failure & Impact level is determined a final level of Risk Rating can be calculated by combining the
Likelihood with the Consequences of Failure for each identified risk. This ascertains an overall Risk Rating for the tree, determined
in Table 2.

Low
Low Moderate Moderate
Low Low Low

 

2 a
Where multiple risks are noted these tables will be used for each risk and the highest level will be taken as the overall risk rating

for the tree. In this scenario multiple mitigation options may be offered to the tree manager to return the risk to an acceptable
level within a reasonable timeframe as guided in Risk Rating.

APPENDIX 3 - DEFINITION OF ISA TERMS

Improbable: | The tree or branch is not likely to fail during normal weather conditions and may not fail in many severe weather
conditions within the specified time frame.

 

 

 

Possible: Failure could occur, but it is unlikely during normal weather conditions within the specified time frame.
Probable: Failure may be expected under normal weather conditions within the specified time frame.
Imminent: Failure has started or is most likely to occur in the near future, even if there is no significant wind or increased load.
ane is an infrequent occurrence for a risk assessor to encounter and may require immediate action to protect people
m harm.

Very low: The likely hood of the failed tree or part impacting the specified target is remote. Occupancy rates are rare with no
protection or occasional with moderate protection.

 

 

Low: It is not likely that the failure will impact the target. The occupancy rates are frequent with partial protection or
constant with significant protection.
Medium: The failure is as likely as not to impact the target. The occupancy rates frequent with single side exposure or constant

with partial protection.
The failure is most likely to im, the target. Occupation is constant with no

 

fection.

 
 

   

Constant: 24 hours a day, 7 days a week.

Frequent: A large portion of the day / week.

Occasional: | The zone is occupied by people or targets infrequently or irregularly.
Rare: Not commonly used.

 

 

 

Negligible: Low-value property damage or disruption that can be replaced or repaired, no personal injury.
Minor: Low to moderate property damage, small disruptions to traffic or infrastructure, or very minor injury to persons.
Significant: | Property damage of moderate to high value, considerable disruption, or personal injury.

Severe: Serious personal injury or death, damage to high-value or disruption of important activities.

 

 

 

   
 

 

 

 

 

 

 

Extreme: Failure is imminent with a high likelihood of impacting the target, and the consequences are severe.

High: Failure is very likely or likely with significant consequences, or failure is likely with severe consequences.

Moderate: Failure is very likely or likely with minor consequences, or failure is somewhat likely with significant or severe
consequences.

Low: Failure is unlikely with negligible consequences or failure is somewhat likely with minor consequences.

 

 

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