VANCOUVER - All ski hill towers must be fitted with drain holes to prevent incidents like the collapse of a gondola tower at Whistler resort that left a dozen people injured, says a report released Tuesday by the British Columbia Safety Authority.

Six gondola cars fell from the Excalibur line at Whistler Blackcomb in December 2008.

The safety authority says water likely entered the tower's cavity through a plate connecting its upper and lower sections and was unable to drain out.

The water then froze and the ice expanded inside the cavity, pushing against the walls and the plate, or “ice-jacking,” triggering the collapse.

At the time of the collapse, the Excalibur gondola had been in service for 14 years with no serious incidents reported.

The safety authority, which oversees the province's passenger ropeways sector, including ski lifts, gondolas and tramways, makes six recommendations in its report.

It says all of B.C.'s ski hill towers must have the drain holes to prevent the accumulation of water and such ice-jacking, as required by a national standard.

“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,” the 73-page report says.

The safety authority has already issued a safety order to ensure compliance with the recommendation.

The report also calls on manufacturers to ensure required inspection procedures are clearly communicated and says passenger ropeway contractors must ensure the effectiveness of their own internal communication.

Dozens of passengers were stranded for hours after the collapse on Blackcomb Mountain, which neighbours Whistler Mountain, the home of alpine events at the 2010 Winter Games.

Most of the injuries consisted of bumps and bruises but one person suffered a fractured vertebrae.

One gondola car hung over a creek as resort and emergency officials worked to stabilize the tower before they could attempt an evacuation.

While the incident on the Excalibur was the first on the line, it was not the first ski lift accident at the resort.

A Dec. 23, 1995, accident on the Quicksilver ski lift killed two men and injured nine other people.

The high-speed lift was ferrying skiers to the top of a run when one chair slipped on a cable and slammed into another, setting off a cascade that sent four chairs crashing into the bush and rocks three storeys below.

A coroner's report said the accident was a result of systemic failure, noting problems with the lift system's grip mechanisms should have been detected in advance.

In January 2006, two empty gondola cars at the Sunshine Village ski resort near Banff, Alta., plummeted to the ground after being dislodged from their cables by high winds. No one was injured.

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