Bushfire Investigation - Cudlee Creek Bushfire (20 December 2019) Office of the Technical Regulator - Department for ...
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Bushfire Investigation Cudlee Creek Bushfire (20 December 2019) Office of the Technical Regulator
Preface This technical investigation report has been prepared by the Office of the Technical Regulator (OTR) pursuant to the objectives, powers and functions conferred on it by the Electricity Act 1996. Specifically, these include, amongst other things the monitoring and regulation of safety and technical standards in the electricity supply industry and the administration of the provisions of this Act relating to the clearance of vegetation from powerlines. 2
Contents
Summary ................................................................................................................................................. 4
Introduction ............................................................................................................................................ 5
Scope ................................................................................................................................................... 5
Objectives............................................................................................................................................ 5
Methodology ....................................................................................................................................... 5
Background ......................................................................................................................................... 5
Declarations ........................................................................................................................................ 7
Technical Investigation ........................................................................................................................... 8
SAPN and CFS Site Observations ......................................................................................................... 8
OTR Site Observations ........................................................................................................................ 8
SA Power Networks Incident Report .................................................................................................. 9
SAPN Protection Equipment Operation ............................................................................................ 10
LiDAR Information ............................................................................................................................. 10
Google Earth Image Review .............................................................................................................. 10
Electricity (Principles of Vegetation Clearance) Regulations 2010 ................................................... 10
Prevailing Weather Information ....................................................................................................... 11
Findings and Conclusions ...................................................................................................................... 12
The Fire Source ................................................................................................................................. 12
Auto Circuit Recloser Operations ...................................................................................................... 12
Vegetation Clearance ........................................................................................................................ 12
3
Summary On Friday 20 December 2019 during severe fire conditions a fire commenced in the vicinity of Hollands Creek Rd, Cudlee Creek, which quickly spread through the Adelaide Hills, causing loss of one life as well as destruction of numerous houses and other assets. In cooperation with the Country Fire Service (CFS) and SA Police (SAPOL) the OTR established the likely cause of the fire start as a tree that had fallen onto an 11 kilovolt (kV) powerline. The point of ignition was adjacent to a pine tree plantation near Holland Creek Rd. The base of the tree that fell was approx. 6.8m horizontally away from the closest conductor. The tree was estimated to be 24m high, hence making it possible for the tree to contact the powerline when it fell over. As the agency responsible for the monitoring and regulation of safety and technical standards in the electricity supply industry the Office of the Technical Regulator (OTR) reviewed the incident to assess if breaches of the Electricity Act 1996 had occurred which might have contributed to the fire start. From the evidence observed on the site and review of information provided by SA Power Networks (SAPN) the OTR determined that the tree that fell was at a distance greater than the minimum clearance distance required by the Electricity (Principles of Vegetation Clearance) Regulations 2010, however due to its height it was able to contact a conductor when it fell. The OTR could not identify any indicators that could have enabled a reasonable person to identify this tree failure prior to the event. Based on the findings of this investigation the OTR concluded that no further technical investigation into this incident regarding electrical infrastructure is warranted. 4
Introduction
Scope
This report details the findings of a technical investigation by the OTR of the causes of and
contributing factors to a fire that originated at a location along an 11kV electricity line with the
feeder ID GU43. The location is approx. 6.5km north‐west of Lobethal.
The investigation details the evidence gathered to support the technical conclusion reached and
outlines the relevant standard that applies to vegetation management near the distribution network
at this location.
Objectives
The OTR’s objectives were to:
Establish whether electrical infrastructure played a role in the cause of the fire;
Determine whether relevant technical standards had been maintained;
Assess if relevant procedures had been followed; and
Provide assistance to other investigating agencies, such as SA Police and the Country Fire
Service.
For the investigation the OTR took the following information into account:
Information provided by SAPN:
o Investigation Report
o Email correspondence
OTR site visit and observations
Discussions with investigators from SA Police and CFS
Google Earth images
Methodology
As part of their investigation the OTR undertook the following actions:
Requesting and reviewing specific information from SAPN, including their investigation
report and reports on the operation of protection equipment
Assessing the information provided against relevant requirements, including legislated
clearance distances and relevant operational procedures
Visiting the location of the fire start, measuring distances between powerlines and
vegetation to establish if any breaches of vegetation clearance zones had been likely prior to
the fire
Meeting with the CFS to seek independent confirmation on the likely cause of the fire
A review of Google Earth historic images
Background
On Friday 20 December 2019 during challenging weather conditions with elevated temperatures and
high wind speeds a fire started near Snake Gully Rd, Cudlee Creek.
With a very high level of certainty it was determined that a pine tree had fallen onto an 11kV
powerline, which started the fire that quickly spread throughout the Adelaide Hills.
5
Figure 1: Fire Start Location For the purposes of maintaining legislated distances between vegetation and powerlines the area where the fire started is classified as a “bushfire risk area” as defined in regulation 3 of the Electricity (Principles of Vegetation Clearance) Regulations 2010. Figure 2: Bushfire Risk Classification under the Electricity (Principles of Vegetation Clearance) Regulations 2010 6
Declarations
A Total Fire Ban and Catastrophic Bushfire Fire Danger Rating for the Mount Lofty Ranges had been
declared by the CFS on 19 December 2020 at 4:22pm.1
A Bushfire Advice Message was first issued by the CFS at 9:22am on 20 December 20202, and quickly
escalated to an Emergency Warning Message for a fire burning in catastrophic bushfire conditions3.
The Bureau of Meteorology on 19 December issued the following advice at 4:32pm for the following
day:
Forecast for Friday 20 December: Very hot. Afternoon cool change. Cloud developing with
dust haze possible in the late morning and afternoon. Slight (30%) chance of a shower or
thunderstorm in the afternoon and evening. Winds northeasterly 30 to 45 km/h increasing
to 50 km/h before shifting south to southwesterly 30 to 45 km/h in the late afternoon.
The CFS information combined with the BoM’s weather forecast for 20 December 2019 resulted in a
forecast SA Power Networks Fire Danger Level Rating of FDL2.
1
https://www.cfs.sa.gov.au/site/home/criimson/cfs_fire_ban_and_fire_danger_rating_issued_19_dec_162400
03552.jsp
2
https://www.cfs.sa.gov.au/site/home/criimson/advice_message_cudlee_creek_issued_20_dec_09230003563.
jsp?display_expired=t
3
https://www.cfs.sa.gov.au/site/home/criimson/emergency_warning_message_cudlee_creek_issued_20_dec_
09330003565.jsp?display_expired=t
7Technical Investigation SAPN and CFS Site Observations Following an initial investigation by the CFS it emerged that SAPN’s infrastructure had likely been involved in the fire start, prompting an internal investigation by SAPN. Both SAPN and the CFS have confirmed to the OTR that the likely cause of the fire had been a pine tree from a plantation that had fallen onto an 11kV powerline. Evidence gathered by the CFS and SAPN and sighted by the OTR appears to strongly support this conclusion. OTR Site Observations Upon confirmation by the CFS that a tree falling onto a powerline had likely started the fire an OTR officer visited the site to assess whether any breaches of clearance requirements under the Electricity (Principles of Vegetation Clearance) Regulations 2010 may have occurred which could have contributed to the fire start. Figure 3: Fire Start Location 8
Figure 4: Fire Start Location
The site observations included:
An established plantation of pine trees exists west of the powerline.
SAPOL or CFS investigators had numbered the first twelve trees in the front row of
the plantation (directly adjacent to the powerlines) with yellow paint.
The OTR was advised that the tree number six had fallen over, with the majority of
the tree completely burned in the fire and only the trunk remaining
The OTR officer measured various distances which are relevant for vegetation
management compliance, including the span length, the location of the tree trunk in
relation to the closest stobie pole and the distance of remaining vegetation of the
other, adjacent trees to the powerlines, as well as the height of the remaining trees.
SAPN Incident Report
In March 2020 SAPN provided their internal investigation report to the OTR, which includes:
A detailed description of the fire start location and equipment involved;
Operational details of SAPN protection equipment on the day;
A description of their inspection and maintenance history of relevant equipment; and
A description of operational procedures on the day of the bushfire.
Three OTR officers assessed this information independently and individually against relevant
procedures and legislated requirements.
None of the OTR officers were able to identify a breach of relevant SAPN policies or legislation
regarding SAPN’s maintenance regime or operations in the lead‐up to and on 20 December 2019.
9Under section 11 of the Electricity Act 1996 the Technical Regulator must preserve the confidentiality of information gained under this Act, such as this report. SAPN Protection Equipment Operation SAPN records show that the primary protection device involved was a recloser. The recloser initially operated at 9:11:55am, and appears to have operated as per the applied settings. SAPN had advised of the last inspection of this recloser, which the OTR determined to be in accordance with their relevant inspection regime. SAPN advised that it had no outstanding defects at the time of the incident. LiDAR Information Following the bushfire fire SAPN undertook a Light Detection and Radar (LiDAR) Analysis of the remaining trees located next to the failed tree, with the assumption that the failed tree would have been similar in growth and height. SAPN’s LiDAR analysis does not indicate that vegetation had breached the prescribed clearance distances. The OTR undertook their independent assessment with a Truepulse 360 range finder at site, with the assessment supporting SAPN’s findings. Google Earth Image Review Historic Google Earth images dating back to 2002 confirm that the forest plantation had been well established at that time, and that there had not been a noticeable change of distances between vegetation and the powerlines in that region over the years. Electricity (Principles of Vegetation Clearance) Regulations 2010 Under these regulations SAPN has an obligation to keep a defined Clearance Zone around the powerline free of vegetation, in accordance with regulation 4 of these regulations. The Clearance Zone for an uninsulated 11kV powerline in a bushfire risk area is defined by clause 4 (3) of schedule 1 of the Electricity (Principles of Vegetation Clearance) Regulations 2010. The OTR measured the base of the tree that fell onto the line to be approx. 13m into the span of the powerlines, which has a total span length of approx. 225m. The base of the tree is approx. 6.8m horizontally away from the line. The horizontal Clearance Zone at that location is 1.77m, as per calculation in the below table. Span length (m) 225 Taper Length: Quarter of the span length (m) 56.3 Tree base location from pole (m) 13 Location of tree base in % of taper 23% Prescribed Clearance at Pole (m) 0.5 Prescribed Clearance in midspan (m) 6 Prescribed Clearance Zone at location of tree base, 23% into the taper (m) 1.77 Table 1: Clearance Zone Calculations The OTR did not observe any vegetation from adjacent, remaining pine trees that were infringing within the Clearance Zone, which lead to the conclusion that the tree which fell onto the powerline would have been unlikely to have been infringing into the Clearance Zone. 10
The OTR considers that the tree fell onto the powerlines from outside the Clearance Zone.
The gradient of the ground is steep up from the pole to the failed tree. In combination with the
estimated height of the tree (based on the height of adjacent trees) the canopy of the tree was
substantially higher than the conductor.
SAPN patrols powerlines in bushfire risk areas on an annual basis and have confirmed that the last
inspection of the line had occurred in January 2019, and vegetation scoping had occurred on 12
December 2019.
The OTR did not observe any circumstances which could have led a reasonable person to foresee the
failure of the tree to fall onto the powerline.
Prevailing Weather Information
The two closest weather stations to the location of the fire start are Mount Crawford and Mount
Lofty. The weather data recorded for these two stations at 9am on 20 December 2019 is shown
below:
Location of
Relative Wind Wind
Weather Temperature
Humidity Direction Speed
Station
°C % km/h
Mt Lofty 33.9 19 N 19
Mount
36.2 16 N 35
Crawford
Table 2: Weather Observations on 20 Dec 2019
Under section 53 of the Electricity Act 1996 SAPN may, without incurring any liability, cut off the
supply of electricity to any region, area, land or place if it is, in the entity's opinion, necessary to do
so to avert danger to person or property.
SAPN has developed detailed guidelines to determine the circumstances when the disconnection of
regions may be appropriate to mitigate bushfire risks from their infrastructure.
The OTR has reviewed these guidelines, the weather data and SAPN’s operations on 19 and 20
December 2019 and has not been able to identify any deviations by SAPN from their procedures. The
available weather data (forecast and actual) did not trigger the pre‐emptive disconnection of the
Mount Lofty Ranges under section 53 of the Electricity Act 1996.
11Findings & Further Steps The Fire Source The most likely cause of the fire was a pine tree falling onto an uninsulated 11kV powerline, with the fire either starting when the tree contacted the line, or when the line subsequently fell to the ground, creating an ignition source that started the fire in catastrophic bushfire conditions. Auto Circuit Recloser Operations The recloser operated in accordance with its normal settings. It initially tripped, then reclosed for a brief period before it permanently locked out. The OTR reviewed the relevant operating protocol and concluded that the recloser settings had been applied in accordance with the established procedures, taking into account forecast and actual conditions on the day. It cannot be determined if the fire was started on the initial trip or the second trip (the reclose). Vegetation Clearance The tree which fell onto the powerline was outside of the prescribed clearance zone. There are no indicators that the tree could have been identified as a risk tree prior to the incident. Following the fire there are burnt pine trees in the vicinity of the powerlines now remaining. The OTR understands that SAPN is working with the land owner to remove those trees that have the potential to fall onto the powerlines by mid 2020. The OTR will monitor the progress on this matter. Given the findings as described in this report the OTR will not further investigate this incident. Further Steps An incident of this nature with a tall tree falling onto an overhead powerline is difficult to prevent. Since having been gazetted in 1996 the Electricity (Principles of Vegetation Clearance) Regulations have prescribed certain exclusion zones when planting trees near powerlines. In the long term these requirements will contribute to the reduction of risk of a reoccurrence of a similar incident. In 2017 the South Australian Government introduced section 55AA to the Electricity Act 1996 which provides electricity network operators with the power to remove trees that are at risk of falling onto powerlines even when these are outside the prescribed clearance zone. This power vested with the network operators will contribute to a risk reduction in the long term. The current Electricity (Principles of Vegetation Clearance) Regulations 2010 will expire on 1 September 2021. Any review and changes to the regulations will strongly focus on mitigation of the risk of bushfires that may start when vegetation contacts high voltage powerlines. With regards to the specific incident there are burnt pine trees remaining in the vicinity of the powerlines. SAPN confirms that the plantation removal began on the on 19th of May 2020 and should be completed within 2weeks. The OTR will monitor the progress on this matter. SAPN has further advised that they conducted its annual post Fire Danger Season review meeting on 11 May 2020 to highlight operational actions that are working well and those that could be improved. Follow up actions will be included in SAPN’s annual Summer Preparations Plan. This Plan 12
includes actions to prepare the SA Power Networks distribution network for the fire danger season and protracted heatwaves. Furthermore, in April 2020, CSIRO was engaged to undertake a review of SAPN’s disconnection procedure and criteria to pre‐emptively disconnect electricity feeders to prevent bushfire starts. The OTR will seek an update from SAPN on this matter prior to the bushfire season 2020/21. Given the findings as described in this report the OTR will not further actively investigate this incident but monitor the progress on outstanding action items as described above. 13
You can also read
