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Beck Diefenbach, Associated Press
Mourners stand by during a candlelight vigil for six Irish students Wednesday, June 17, 2015, in Berkeley, Calif. The six Irish students died when a balcony collapsed during a party.

BERKELEY, Calif. — Rotting wood and other issues can cause balcony collapses, sometimes with terrible consequences.

Six people died Tuesday in Berkeley, California, when a balcony failed and an estimated 6,500 people were injured in deck failures in the past decade.

However, the Consumer Product Safety Commission, which analyzed emergency room visits for The Associated Press, found deaths are rare from collapses. Before the accident in Berkeley, there had been just 23 fatalities since 2002.

The review estimated that 4,600 emergency room visits were associated with deck collapses, and another 1,900 with porch failures.

With millions of ER visits a year in the U.S., "the type of incident that happened in Berkeley appears to be rare," commission spokesman Alexander Filip said based on the data collected from 100 hospitals to make the projections.

One of the worst collapses occurred in 2003, when a porch collapse in Chicago killed 13 people. The commission identified just 10 fatalities that occurred since then.

Those 10 fatalities do not include the students, including five from Ireland, who died while seven others were injured in Berkeley when a crowded deck cracked from a building, tossing them 50 feet to the pavement below.

Family members who arrived from Ireland were planning funerals and visiting Thursday with those who were injured.

Experts and city officials have said the 40 square foot balcony might have snapped off because supports had dry rotted, a problem that structural engineers say can be prevented through proper design, construction and maintenance aimed at sealing out water.

Left unrepaired, dry rot can weaken balconies and create collapse hazards, said structural engineer David Helfant, who has inspected thousands of decks and balconies.

"It's all about creating a safe structure that has endurance, that has a reasonable life expectancy," said Helfant, who identified potential flaws in design and construction after inspecting the Berkeley balcony that collapsed.

"When I see something like that in a town I work and live in, it's extremely depressing, it's upsetting," he said.

Dry rot occurs when water gets into poorly ventilated areas of buildings and a fungus starts to decay the timber. If left unchecked, wood can fall apart or turn to powder.

The Berkeley apartment complex was built by Segue Construction and completed in 2007. Company spokesman Sam Singer said the firm has never "had an incident like this in its history."

Attorneys Thomas Miller and his daughter Rachel Miller, who specialize in construction defect lawsuits, say water problems — mold and dry rot — are the biggest culprits in such legal actions.

"Nearly every case is because of water," Rachel Miller said. "Water gets into the building. You have to anticipate that's going to happen."

The Millers haven't handled any collapse cases. But they have sued and settled lawsuits that allege balconies have incurred dry rot.

Balconies are now being repaired at a Millbrae, California, condo complex, another Segue project, because of a lawsuit the Millers filed in 2011.

Thomas Miller said landlords and property managers "have to expect that people will use balconies" and that they are required to ensure the balconies are safe, including being free of dry rot.

Miller says property managers and condo associations are required to inspect balconies annually.

The Rev. Aidan McAleenan said families were focusing on their loved ones rather than why the crowded fifth-floor balcony failed during a 21st birthday party held by visiting Irish college students.

"We may well wonder and want to lash out and talk about the balcony and who built it," McAleenan said Wednesday evening at The Cathedral of Christ the Light in Oakland. "But at the end of the day, what (families) want the most is to see their loved ones. They want to touch them, they want to hold them and they want to kiss them."

The students who died were Ashley Donohoe, 22, of Rohnert Park, California, and Olivia Burke, Eoghan Culligan, Niccolai Schuster, Lorcan Miller and Eimear Walsh, all 21-year-olds from Ireland.

Autopsy results showed their causes of death as multiple blunt injuries.

A funeral for cousins Donohoe and Burke is planned Saturday at St. Joseph's Catholic Church in Cotati, California.

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Mendoza reported from San Francisco. Associated Press writers Kristin Bender, Paul Elias, Ellen Knickmeyer, Janie Har and Terry Chea in San Francisco, and Danica Kirka in London contributed to this report.