Weaknesses in the concrete used for the roof of a futuristic Paris airport terminal were the main cause of its collapse that killed four people on May 23, an official report said on Tuesday.

The initial findings by an investigative commission did not apportion blame or comment on the future of the terminal, which was built at a cost of EUR750 million (USD$920 million) and could be demolished if its structure is fundamentally flawed.

The Transport Ministry said it was still not completely clear why the accident happened at Terminal 2E of Charles De Gaulle Airport more than two years after it was built.

"The view of the commission is that the main cause of the sudden collapse is linked to the perforation of the concrete roof by the struts (supporting it)," the ministry said of the initial findings.

"It is likely that this perforation was facilitated by the prior and gradual weakening of the concrete," it added.

The terminal was designed to handle 10 million passengers a year. Permanent closure of the showcase building would be a big blow to the finances and image of operator Aeroports de Paris (ADP) as it prepares for partial privatization.

Part of the terminal was opened to staff last month but ADP has pledged to raze the cylindrical boarding-area building to the ground if the structure is found to be fundamentally flawed.

Jean Berthier, the head of the investigative commission, told a news conference much more work had to be done searching through the rubble and ruins.

"Several more months are needed but we have been asked to work quickly," he said.

Berthier said it was important to find out why part of the terminal had collapsed at this particular time and not sooner. He said other factors, such as big temperature differences in various parts of the terminal, should be investigated.

A public prosecutor is carrying out a separate inquiry into the collapse, which could establish who is to blame.

The terminal was used mainly by national carrier Air France and was opened just over a year ago.

Hailed as a triumph of engineering and design, the terminal has a domed roof dotted with windows bathing it in light. But the collapse raised questions both about its design and whether it was built too fast.

The report said it was unlikely that the collapse was linked either to the foundations of the building or to the pillars on which the whole terminal was supported above the ground.

(Reuters)