BC Safety Authority makes six recommendations following investigation of ski lift tower ice-jacking
BC Safety Authority (BCSA) released today a detailed 73-page report with six recommendations following its investigation into the collapse of a tower on the Excalibur Gondola line in Whistler Blackcomb.
The accident, which happened on Dec. 16, 2008, caused injuries to 12 of 43 passengers riding the lift at the time of the collapse, based on information received during the investigation. Six of 33 cabins were also damaged when the top section of a tower separated from the lower section and fell to the ground.
According to Jason Gill, BC Safety Authority’s safety manager for passenger ropeways, water entered the tower’s cavity, probably through a plate connecting the tower’s upper and lower sections, and then froze after it was unable to drain out. A rectangular opening on the plate -- used to pour concrete into the lower section during the tower’s installation -- and a flame-cut bolt hole are both believed to have provided a pathway for water to enter the tower.
Unusually cold temperatures in the Whistler area before the incident froze the water which had collected in the lower section of the tower. The ice then expanded inside the cavity, pushing against the walls and the plate, eventually causing the tower to collapse.
BC Safety Authority has regulatory oversight of the province’s passenger ropeways sector, which includes ski lifts, gondolas, tramways, rope tows and passenger conveyors. BCSA also regulates six other industries: electrical, gas, railways, amusement rides, boiler and pressure vessels, and elevating devices.
The Excalibur Gondola had been in service for 14 years at the time of the tower collapse and had no serious incidents reported, said Gill.
As a result of the investigation, six recommendations have been made to help prevent a similar incident from happening again:
- All ski hill towers in BC must be fitted with drain holes or other means to prevent the accumulation of water, as required by the national standard.
- Manufacturers must make sure that required inspection procedures are clearly communicated.
- Contractors must make sure that manufacturers’ safety bulletins are followed by staff, and that inspection and test results are properly documented.
- Manufacturers must make sure that “as built conditions” are documented and transferred to the owner and operator during installation.
- BCSA will submit its findings to the national CAN/CSA Z98 Technical Committee for review and possible code changes.
- BCSA will improve processes to make sure its safety officers are aware of and document manufacturers’ safety bulletins.
Gill has also issued this week a Safety Order to ensure compliance with the first recommendation noted above.
British Columbia Safety Authority keeps people safe by mandating the safe installation and use of technical equipment. As the province’s delegated authority, BCSA administers safety standards, enforces compliance, issues permits and licences, educates, conducts onsite inspections in high-risk situations and continuously advances the standards of safe practices in BC.
Additional Background Attached:
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In the early afternoon of December 16, 2008 the lower section of Tower #4 of the Lower Excalibur Gondola passenger ropeway cracked resulting in the top section completely separating from the lower section of the tower. The top of the tower then fell to the ground in an upright position supported by the communication cables attached to the top of the top section.
At the time of the failure, the Excalibur lift was carrying a total of forty-three passengers.
Following efforts taken to secure the lift, these passengers were immediately evacuated by ski patrol staff and local emergency services. Twelve passengers were injured. Their injuries ranged from a fractured vertebra and concussion (reportedly the most serious injury) to bruises and contusions.
The Excalibur lift was also damaged as a result of the tower failure. Six of a total of thirty-three cabins were damaged to various degrees. Several of the ropeway sheaves, which are fitted to the top of the towers to carry the lift rope were damaged and the lift rope itself suffered minor damage.
Intrawest the owner and Blackcomb Skiing Enterprises Ltd. the operator of the Lower Excalibur Gondola passenger ropeway, informed the Provincial Safety Manager in accordance with regulations. The Provincial Safety Manager requested the site to be secured and dispatched a Safety Officer as a first step in starting a formal investigation of the incident. The operating permits for both the lower and upper Excalibur Gondola lifts were suspended pending investigation and repairs.
The BC Safety Authority initiated an investigation into the failure incident consisting of the following primary activities or elements:
- A review of the various metallurgical tests and examinations undertaken by Acuren, which was commissioned by Intrawest, on the section of the tower where the crack initiated and subsequently failed,
- A review of Intrawest’s inspection and maintenance records for the lower Excalibur Gondola lift was undertaken,
- Analysis of all documents obtained during the on site investigation including witness’s statements,
- A review of various codes and standards that apply to the design, inspection, maintenance and operation of this type of Gondola lift,
- An independent analysis of the Acuren findings undertaken by Pol-X West,
- A root cause analysis of the incident undertaken by a multi-disciplinary team within BC Safety Authority, and
- Identify recommendations to prevent future occurrences.
Tower #4 was designed by the manufacturer to be sealed to prevent water ingress and exposure to oxygen to inhibit corrosion of the inside of the tower tubes. However, over the 14 years since the Excalibur lift was installed, water did enter the tower inner cavity collecting in the lower section. The water accumulated above a column of concrete that was poured into the lower section of the tower during its installation. Although tests for water accumulation were conducted during periodic inspections of the tower, the test, called a resonance or dead blow hammer test, did not detect the water in the tower. The test method is dependent on the tester’s knowledge of the tower’s “as built” construction such as the level of concrete within the tower cavity as well as, previous test experience and adequate test instructions. The use then, of the hammer blow test to confirm the presence of water within a tower is not always definitive. The records of inspections carried out on Tower #4 and results of the resonance testing undertaken were vague making an accurate assessment of the reliability of the testing difficult.
Between December 13 and December 16, 2008 a cold front dropped temperatures in the Whistler-Blackcomb area to as low as -15°C, well below the seasonal average of -3.2°C. The water inside the lower tower section froze causing a column of ice to form on top of the concrete. As the water froze, the ice expanded. The ice then began imparting a longitudinal force onto the splice coupling plate, as well as an axial force directly onto the weld of the splice coupling plate.
Acuren’s report identified the failure mechanism as being a brittle fracture that started in the weld that joined the splice coupling plate to the lower tube section. Acuren also indicated that there were two other factors, which may have contributed to the fracture of the weld:
- Results of metallurgical tests of the steels used in the tower indicated reduced toughness at lower temperatures and therefore potentially more susceptible to brittle fracture, and
- A pre-existing crack within the weld may have contributed to the start of the December 16 brittle fracture.
The Provincial Safety Manager is of the view the forces created from the expansion of the ice were the primary contributors to the stresses that initiated the December 16 crack causing the tower to fail; the tower was not designed to withstand the forces of the expanding ice column. Other factors such as low temperature toughness, the preexisting crack and stresses from independent loadings such as those that occur when a gondola passes through a tower’s sheaves may have contributed to the failure stresses. However, based on the information available to the BC Safety Authority at the time of this Report the BC Safety Authority cannot definitely conclude whether such additional loadings did or did not contribute to the failure.
These findings have led to the BC Safety Authority to make the following recommendations as a means of reducing the risk of a similar failure occurring in the future:
- All operators of passenger ropeway installations must assure towers are fitted with drain holes or have equivalent strategies in place to prevent the accumulation of water as required in the CAN/CSA Z98 standard.
- Manufacturers must ensure the required inspection procedures, as described in the safety bulletins, clearly and effectively communicate all requirements to undertake an effective inspection.
- Passenger ropeway contractors must verify the effectiveness of their internal communication processes to ensure that manufacturer’s safety bulletins are followed correctly by staff and that the results of any inspections or tests are properly recorded and documented.
- Manufacturers must ensure ‘as built conditions’ are properly documented and transferred to the owner/operator as an integral part of the installation process.
- BCSA will submit the findings of this report to the CAN/CSA Z98 Technical Committee for review and discussion of possible code changes.
- The BC Safety Authority shall improve their internal communication processes to ensure Safety Officers are aware of and understand the safety bulletins issued by manufacturers as well as improve the rigor of documenting this process.
Observation 1 - Installation of Drain Holes:
When designing tower structures the Z98 standard requires that the possibility of corrosion be considered and addressed including, if warranted, drainage to prevent water accumulations. Doppelmayr’s design appears to have been reliant on sealing tower tube structures from any external source of oxygen or moisture to prevent internal corrosion. Based on this design philosophy to seal the towers, the installation of drain holes was not considered necessary by Doppelmayr. In 2006 Doppelmayr made their customers aware of an incident that found maintaining an adequate seal over the service life of a tower proved not to be effective. Doppelmayr attempted to correct this by requiring drain holes only when water intrusion is detected.
Status: The Provincial Safety Manager issued Safety Order SO-P4 0910021 to all operators of passenger ropeways identified in Doppelmayr Safety Alert Bulletin 08-021 Wolfurt KD08003E. The safety order required confirmation from all affected operators to confirm compliance with the Doppelmayr bulletin by November 15, 2009. All responses to Safety Order SO-P4 0910021 to confirm that the required work is complete have been received by the BC Safety Authority. The Provincial Safety Manager has issued a second safety order to all operators of passenger ropeways not affected by the Doppelmayr safety alert bulletin requiring confirmation that drainage provisions are in place in tower structures. The Safety Order requires that operators who identify towers without drainage in place that the manufacturer or a professional engineer be consulted to determine a method to be put in place to prevent the accumulation of water. The safety order requires this prior to the 2010/2011 operating season. Inspections of towers following this incident found that the resonance test alone failed to detect when water had accumulated in the tower cavities.
Observation 2 – Clear and Effective Safety Bulletins:
The ‘resonance’ inspection method used to detect water intrusion is too subjective in determining the presence of water. Further research by the Provincial Safety Manager found that this inspection method is ineffective in some instances based on results of tower drilling conducted by passenger ropeway contractors following this incident. This included towers where no concrete stabilization efforts were utilized. The test is based on the judgment of the person conducting it which is impacted by their level of knowledge of the as built details of the tower and their experience in the use of the test. The Doppelmayr bulletin issued in 2006, SA-06-022 Tower Failure due to Water Intrusion did not warn of the possibility that concrete may be found in towers of similar design and that the level of concrete must be known in order to differentiate whether the lack of resonance is due to water or other factors such as the presence of concrete.
Status: Doppelmayr issued Safety Alert Bulletin SA-08-021 requiring the installation of drain holes in all tube tower sections on passenger ropeway installations world-wide. The installation of drain holes will require annual inspections to ensure that drainage has not become blocked and the inspections must be conducted in the fall season. This way any blockages that may have occurred in the spring and summer will be detected and corrected prior to the occurrence of freezing temperatures. A recommendation has been put forward to the Z98 Technical Committee Chairman to implement a standardized safety bulletin format to be used by all passenger ropeway manufacturers. A standardized format would introduce a consistent approach by all manufacturers and the reader would always know where to find crucial information related to the safety issue and what actions are required to be taken.
Observation 3 – Contractors Internal Communication Process:
The Provincial Safety Manager found that details from the SA-06-022 Safety Alert Bulletin issued by Doppelmayr were not included in the work orders issued to field staff at Whistler-Blackcomb. The required ‘resonance test’ was identified on the work order but no other information was provided. A system is in place at Whistler-Blackcomb to notify the persons responsible for implementing safety alert bulletins that a bulletin has been issued and those persons are required to sign off that the bulletin has been read and understood. If the person conducting the inspection was alerted to the circumstances of the issue, better results may have been achieved and the lack of knowledge regarding the level of concrete within the tower could have been questioned.
Status: Immediately following the incident, Whistler-Blackcomb maintenance staff implemented a system to attach safety bulletins to work orders generated as a result of the issuance of safety bulletins. The Provincial Safety Manager already requires that passenger ropeway contractors identify similar systems in their safety management plans and will use the knowledge gained from this investigation during audits of these plans to improve their effectiveness. A communication will be issued to all passenger ropeway contractors identifying the recommendations in this report at the time of the report publication.
Observation 4 – As-Built Conditions Identified:
The drawings submitted by Doppelmayr at the time of the installation did not identify the ‘as-built’ conditions with regard to the level of concrete inside the lower tube of tower 4. Not knowing the level of concrete made it difficult to determine if there was water above the concrete fill and therefore was detrimental to the effectiveness of tower inspections to determine possible water ingress. As per Appendix A of Z98-M91, the national standard at the time of construction, clause 3.36.2 required that the manufacturer must supply all technical information prior to the inspections and tests required by the standard. This requirement does not clarify that all As-built conditions must be identified; however it is critical that all construction details be provided to assist operators in their required tests and inspections.
Status: The Provincial Safety Manager is now taking steps to verify with the manufacturers if concrete stabilization efforts were utilized in other installations already in place in British Columbia as well as when it is used in future tower designs. Doppelmayr customers were required to locate the concrete level in towers to determine the proper location to install drain holes as required by Doppelmayr Safety Alert Bulletin SA-08-021. The Provincial Safety Manager will be taking action to ensure that all operators of passenger ropeways have knowledge of existing tower installations where concrete has been included in the structure and to what level to assist in determining where drainage should be installed. All future documentation submissions will be required to identify concrete levels within tower structures on tower drawings where necessary. A recommendation will be put forward to the Z98 Technical Committee to clarify that all final drawings submitted by the manufacturer must identify as-built conditions in order to assist with required inspections and tests.
Observation 5 - Technical Committee Review:
In the interest of complete transparency the Provincial Safety Manager must bring this topic forward for discussion at the next CAN/CSA Z98 technical committee meeting. As a member in good standing of this committee it is incumbent upon the Provincial Safety Manager to ensure that a discussion takes place at a national level to determine if code revisions are necessary as a result of this incident and the subsequent investigation.
Status: The Provincial Safety Manager has submitted a formal request to the Z98 Technical Committee Chairman to include this topic on the agenda of the next committee meeting in June, 2010.
Observation 6 – The BC Safety Authority’s Safety Bulletin Process:
The BC Safety Authority does not have records of communication with passenger ropeway contractors regarding bulletin SA-06-022 issued by Doppelmayr in 2006. Standard practice of safety officers would be to discuss any recently issued bulletins with passenger ropeway contractors as they receive them. However this policy is not documented. As part of the BC Safety Authority’s oversight efforts a policy should be developed to follow up on safety bulletins to ensure they are implemented by the passenger ropeway contractor, who is responsible to ensure that manufacturer’s requirements identified in safety bulletins are followed.
Status: A system to confirm that safety officers have received and understood bulletins has been implemented using electronic mail. This system is being assessed to determine if further enhancements are required. A similar system is in place to notify contractors and confirm their receipt for more serious safety bulletins. The regular follow up on all received bulletins through periodic on site inspection will continue. An automatic email notification system is now part of the BC Safety Authority website.