The Olympic Stadium has cracks in several of its concrete supporting structures, documents obtained by Radio-Canada's investigative program Enquête show.

The Olympics Installations Board insists the roof is safe, despite cracks found in part of the stadium's supporting structures. (CBC)The Olympics Installations Board (OIB) confirmed Wednesday that cracks were found a few years ago on five voussoirs, which form part of an archway. The archways, or consoles, act as the stadium's ribs.

The stadium has 34 consoles, and each has a head voussoir.

"There are five of those head voussoirs that will need some repair once we're ready to change the roof, but there is no emergency and no danger whatsoever," said Sylvie Bastien, communications director for stadium.

Despite the reassurances from the OIB, some engineers find the cracks worrisome, especially with a new steel roof on the way.

The OIB has put out a call for tenders for the stadium's new $300- million roof, which will be rigid, fixed and weigh more than 3,500 tonnes.

"It worries me because the cracks are found in the sections that carry the most load and stress," said Claude Phaneuf, the engineer in charge of the Olympic building site from 1971 to 1976.

The roof of the stadium known as the Big O is already in rough shape. The membrane roof has lost nearly 50 per cent of its tear resistance and requires repairs more than 50 times a year.

Cracks were found a few years ago in five of the stadium's head voussoirs, seen in this diagram. (CBC)The structural repairs are "feasible, it's not that big an issue … there's cracks and there's a way to repair them and to reinforce the voussoirs," said Charles Chebl, a vice-president with SNC-Lavalin, one of the companies bidding on the contract.

However, the head of a competing firm said the repairs will be costly.

"They will have to reinforce all the consoles and the head voussoirs that are cracked," said François Delaney of Laboratoire CFD. "They will probably have to be replaced."

In June, the OIB announced it intended to sign a contract with SNC-Lavalin to replace the roof, but the board had to reissue a call for tenders after changing some of the contract's details.

The bidding closes on Friday.