2.3.6 Alphabetical list of common tree hazards
The following section contains a list of common tree-specific hazards that may be encountered by rescue crews , presented in alphabetical order with some brief notes on each hazard .
This list is not intended to be comprehensive ; many other possible hazards can be present in trees . In addition , other possible site hazards that may be present on any work site are not discussed .
The risk posed by each hazard will depend on the rescue plan and the extent or severity of the hazard . Dwayne Neustaeter ( 2003 ) suggested a method of identifying the magnitude of the hazard posed by different tree defects using the ‘ flag ’ system shown below . Some possible control measures are suggested for each hazard to minimise the risk .
Risks
SEVERE HAZARD
The hazard shown may impose a high risk on tree rescue operations . If the hazard affects the trunk , or structural timber that will be loaded during tree rescue operations , it may be easy to cause a structural failure .
Rescue plans should be selected that avoid significant loading on any part of the tree structure where a significant hazard has been identified .
Control measures
A strong , reliable control measure that should be adopted whenever there is concern regarding a defect .
In general , if the control measure can be successfully implemented , the risk should be all but eliminated .
A less reliable control measure , that may adequately control the risk but may have limited effectiveness .
For example , the use of a load test where a compromised part of the tree structure must be rigged off for rescue . The load test will help to confirm the strength of the structure , but may be hard to conduct to a full rescue load at the intended angle .
A control measure that has significant potential uncontrolled risks .
For example , the use of strapping to control a split will reduce the risk of failure , but it is hard to estimate the effectiveness of the control or the residual strength of the tree .
Usually a last-resort rather than a preferred control measure .
MODERATE HAZARD
The hazard shown may still pose a significant risk to tree rescue operations in this tree , but it is likely that control measures or an adjustment to the work plan can eliminate or minimise any risk . Implement suitable control measures , consider the likelihood of failure and proceed with caution .
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