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Paul de Mar

Risk management consultant

GHD

UAAA

Monday 8th April | 4:15pm

TALK TITLE

Clear to Sky overhang removal requirements – what risks are we managing and creating?




BIO

Paul is a vegetation and bushfire risk management consultant with professional services consulting firm GHD.


Paul’s career background is in forestry. From 1996 to 2007, Paul was the chief fire officer for State Forests of NSW (now Forestry Corporation of NSW). With > 250,000 hectares of pine and eucalypt plantations and > 2 million hectares of native forests managed for timber production, Paul’s role was to manage the substantial risk of bushfire to the plantation and forest estate, and lead State Forests annual fire preparedness and response operations, including through a number of severe bushfire seasons including the adverse 2002/03 fire season.


For the last 17 years, Paul has been providing vegetation management and bushfire risk mitigation consulting services across Australia. A significant proportion of Paul’s work is with the electricity supply industry. From his forestry career background and keen professional interest in silviculture, Paul has developed a deep understanding of the growth habits of eucalypts in particular, including how regenerating forest stand structure changes over time in response environmental factors and competition, and how trees respond to injury and damage. Tree and branch failure are a major hazard for firefighters and a leading cause of firefighter fatalities, hence dangerous tree recognition and management has long been a key area of professional interest and study.


Founded on this knowledge and experience in tree growth dynamics and tree hazard management, for the past 15 years Paul has been working across the electricity sector, in both transmission and distribution, providing a range of services from reviews of utility vegetation management strategy and practice, to annual vegetation management program work volume prediction, to more specialised bushfire risk mitigation advisory services and auditing. A key work area has been the provision of expert witness services in relation to vegetation-caused fires, and in particular to best management practices for utility vegetation management. This body of work has allowed Paul to see and compare the approaches taken by different electricity utilities around Australia for vegetation inspection and program management.


In his presentation to the Arboriculture Australia 2024 Annual Conference, Paul will focus on the issue of branch overhangs and branch failure.

ABSTRACT

Electricity supply industry vegetation management regulatory frameworks around Australia establish a variety of requirements for the maintenance or removal of tree branches which grow above regulated clearance spaces applicable to power lines. Specific requirements vary between jurisdictions (eg between applicable voltages), but are broadly similar conceptually. Although it may not be explicitly stated, the general aim is to mitigate the risk of branches (including live and healthy branches) falling onto overhead conductors. These overhanging branch clearance requirements are commonly referred to as ‘Clear to Sky’ provisions.


The practical effect of Clear to Sky provisions is that vegetation cutting crews are required to cut back overhang branches of trees adjacent to powerlines, typically not just to the extent of the line location, but to the full extent of the horizontal clearance space applicable to the line, and in some cases also including above the

‘regrowth space’. The overwhelming majority of overhang branches cut will be healthy structurally sound branches, noting that separate ‘fall-in hazard’ provisions are applicable to dangerous branches with visually obvious structural defects. The circumstances of individual trees (in particular their degree of proximity to the lines and tree height) can result in a variety of different branch cutting and tree-shaping technique applications and effects. While these serve to clear overhanging branches they can also have collateral impacts to the trees from which they were cleared.

Where trees adjacent to powerlines are tall-growing species, overhang clearance can involve branch removal work at substantial heights, in some cases significantly above the reach of commonly used elevated work platforms, thus requiring specialised equipment and crews.


There has been little research into the actual degree of line-strike hazard posed by overhanging branches and limited failure data collection for branches which have fallen and stuck lines, thus the degree of risk reduction actually achieved through Clear to Sky provisions is poorly quantified.


This presentation outlines some of the key issues arising with application of ‘Clear to Sky’ provisions and considers some key elements of native tree growth habits and how these can contribute to different levels of branch failure hazard. Given the general dearth of overhang branch failure research and failure data collection and analysis, it is hoped the this presentation may promote improved data collection and research to support a more nuanced approach to tree overhang management.

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