Commuters are taking a detour Monday around a heritage building in downtown Ottawa that partially collapsed three days earlier. Meanwhile, municipal inspectors are trying to determine whether the building can be saved.

Somerset Street West will be closed from Kent to O'Connor streets and Bank Street will be closed from Maclaren and Cooper streets until further notice, an Ottawa police news release said Monday.

A rear wall of Somerset House partially collapsed Friday, along with the first and second floors of the four-storey heritage building.
(CBC)

An earlier release said the roads would be closed for about a week while engineers investigate the building at the corner of Bank and Somerset streets, which housed the Duke of Somerset pub.

Building inspectors from the city and and safety inspectors from the Ontario Ministry of Labour were both at the site Monday. 

It is believed the collapse took place after a Bobcat machine backed into a masonry column during renovations, said Peter Black, manager of building inspections for the city.

In such older buildings, single columns can carry an enormous load, he added.

"That's the way they used to build them," he said, adding that toppling columns can lead to a "catastrophic failure" of a structure.

The first and second floors fell down around 3 p.m. Friday as five workers excavated in the building's basement, said an Ottawa paramedic service news release. A rear brick wall also collapsed.

The workers received only minor injuries. One of them, a 44-year-old man inside the cage of a Bobcat excavator he had been operating, was trapped in the rubble for more than an hour before he was freed by firefighters.

Firefighters were to stabilize the building and then turn it over to the Ministry of Labour, district fire chief Lyle Fraser said Friday, who said the entire building was at risk of collapse after the incident.

In May, the building's owner, Tony Shahrasebi, said that the Ministry of Labour had closed the work site on at least one occasion over safety concerns prompted by the fact that the workers were not wearing hard hats.

Several of the workers on the site Friday were wearing shirts that identified them as employees of Shahrasebi's Minute Car Wash.