Alberta officials are investigating another incident at a downtown Calgary construction site, this time involving the failure of a small crane.

The mobile crane, which was roped to the Bow building, fell off the third storey on Saturday, smashed into some windows and was left dangling over the construction site.

A mobile crane fell from the third storey of a construction site on Saturday, smashed into some windows and was left dangling. (Nelson Hein/Incremental Photo)"There was a hoist that was lifting a window panel, and the hoist failed, and the window panel fell approximately 20 feet," said Chris Chodan, a spokesman for Alberta Employment. "And as a result of that, the hoist has been removed to be inspected and certified, and we have Occupational Health and Safety officers investigating it."

The worker operating the crane at the time was not hurt.

The Bow complex, located on Centre Street between Fifth and Sixth Avenues S.E., will be the new headquarters for EnCana Corp.

Matthews Developments, which is building the Bow, said safety protocols "worked as designed" on Saturday.

"Tethering prevented the crane from falling, and no injuries were sustained," said the company in a statement. "Repairs to the equipment will be made quickly, and Matthews will assist Alberta Occupational Safety and Health in its required investigation."

The failed crane is the latest in a string of construction-related incidents in the downtown area.

A piece of scaffolding blew off the 19th floor of the Penn West Plaza building on Ninth Avenue on Saturday. No one was hurt.

On Aug. 1, Michelle Krsek, 3, was killed after being struck by a piece of corrugated metal. High winds had blown the roofing material from the 18-storey Le Germain hotel and condo site at 112 Ninth Ave. S.W.

The developer and builders of the highrise were charged on Friday with violating the Alberta Safety Codes Act.