Irish students Berkeley deaths
Workmen examine the damage at the scene of an apartment building balcony collapse in Berkeley, CaliforniaReuters

Flags flew at half-mast in Ireland Wednesday and heartsick families landed in California to mourn the young Irish students killed in a tragic balcony collapse as they celebrated a friend's 21st birthday.

Five of those killed in the accident near the University of California at Berkeley were visiting from their homes in Ireland for the summer to work and travel in America. The sixth victim, who lived in California, had dual Irish-American citizenship and was a cousin of another killed in the collapse.

"The tragedy is that they were heading out full of life and full of the joys of summer," said Father Frank Herron at a vigil mourning the dead at Our Lady in Foxrock Church in south Dublin.

Seven others remain in hospital, many of them with serious injuries.

Officials ordered the owner of the Library Garden Apartments where the accident occurred to remove what was left of the balcony and conduct a thorough examination of the structure. An early examination indicates that balcony supports may have been undermined by seeping water causing dry rot.

"It appears to be a classic case of dry rot, meaning water intruded into the building and rotted the wood" that supported the balcony, Oakland engineer Gene St. Onge told the Los Angeles Times. "It gave way. It didn't have enough residual strength, and it failed."

Wooden beams protruding from the building where the balcony once stood show what looks like signs of dry rot. "It appeared to be shredded and darkened and had all the appearance of wood that had been totally compromised by dry rot," said St. Onge.

A former Berkeley city official told the San Francisco Chronicle that the small balconies at the apartment complex were largely decorative, and not intended for the 13 people who packed the space. "This was meant just to be a place where someone could stand out for bit, get a breath of fresh air," said Carrie Olson, a member of the Berkeley Design Review Committee that approved the project in 2001.

"It seems that those students were just doing what young people do, crowding onto a balcony," she said. "But it's up to us, not them, to make this stuff safe."

It was not immediately clear if there were any warning signs limiting the number of people who could safely use the balcony. Apartment owners typically don't post weight limits for balconies and aren't required to by law, a Berkeley structural engineer told the Chronicle. The balcony was about 30 square feet (9 square meters).

The victims were identified as Olivia Burke, Eoghan Culligan, Lorcan Miller, Eimear Walsh and Niccolai Schuster, all 21 years old, who had traveled to the Bay Area for the summer on J-1 visas.

The sixth student, 22-year-old Ashley Donohoe, lived in Rohnert Park, 50 miles north of San Francisco. She and Burke were cousins.

Another visiting Irish student, Conor Travers, was with the party group before the accident in downtown Berkeley also celebrating the 21st birthday, but opted not to return to the apartment where the accident occurred at the end of the night.

His mother, Ann Travers, told the Guardian she would give Conor "the biggest hug of his life" when he returns from California to her home in County Wicklow.