Calgary should consider new safety standards for attaching windowpanes to skyscrapers in the wake of several cases of glass shattering on the streets below, says an architect and professor.

A pane of glass fell from the corner of the 23rd floor of Brookfield Place on Sunday morning, smashing on the pavement.

Two weeks earlier, a window-washing crew broke a window on the same building. The broken glass forced bus and C-Train routes to divert away from the tower.

No one was hurt in either case.

brookfield tower glass fell

This closeup shows the missing glass on the 23rd floor. Two weeks earlier, a window-washing crew broke a window on the same building. (CBC)

Many European countries have rules requiring that glass panes be mechanically secured to skyscrapers to prevent them from falling during strong winds, University of Calgary architecture professor Maurico Soto Rubio told the Calgary Eyeopener on Tuesday. He spoke with host David Gray.

Q: We don't know exactly what happened downtown. There were high winds that day, so of course that's the speculation, that it was a wind thing. Is it possible for wind to rip out a part of glass from a skyscraper?

A: Absolutely. This is a well known issue that we architects have been dealing with for the last, you know, 50 years or more. Wind speed actually increases drastically, exponentially with height. 

Every time in the City of Calgary when we hear that we can have gusts of winds of up to, let's say, 100 kilometres per hour, that's really at ground level. That's really what we experience in, let's say, the first 10 metres. But as we go higher, that wind speed is increasingly, exponentially higher. It can be twice as much.

Q: You could have 200 kilometres howling wind 200 metres above the street?

A: Absolutely. Something important to understand is that wind can create not just wind pressure, positive pressure pushing on a building, but we can also have suction. Some of this negative pressure can, in fact, suck window panels out of the frames.

Q: But we've been building glass towers in Calgary, well, it seems like a long time now. Designers love the glass tower, don't they? That solid wall of glass. Are our regulations different from other cities or other places when it comes to installing glass on an office tower?

A: Yes, in some European countries, for example, architects and engineers are required to actually have mechanical details that hold the glass in place.

So the glass is not just held on the side of the building by silicone, but you need to have some mechanical elements that screw down the glass panel in place.

Q: Because the danger is high. We've been lucky in Calgary when this happens. It was like on a Sunday morning, I think. But think about the forces of that size of a sheet of glass falling from that height.

A: Absolutely. I mean, we're talking about a glass panel that can weigh about 200 pounds easily. Now there's something that I noticed just by looking at the pictures, is that the glass panels, they seem to be falling out of the corners of the building. That's not coincidence. [Suction] depends on the height, the velocity of the wind, the wind speed, the direction of the wind and also the shape of the building itself.

Mauricio Soto Rubio

Mauricio Soto Rubio is an architecture professor at the University of Calgary. He worked in Europe, where glass panes must be mechanically secured to skyscrapers. (CBC)

But [a curve] tends to be more serious and produce more suction around the corners of buildings.

Q: You're from Spain originally and you spent 10 years working on basically this field in Germany. Is it time for changes in code in Calgary? Do we need to start doing what they do over there, and start mechanically attaching our glass windows?

A: Of course there are many issues involved. We should not be having glass falling out of buildings, if everything is followed and controlled correctly. However, things happened. It's hard to say exactly what the wind speed is going to be 200 metres above ground at any given time during the year. And it's always a good idea to have some kind of safety net.

Q: The investigation's ongoing. We'll wait and see what they find. But in the short term, if I can be blunt, let me ask you: on a windy day in downtown Calgary, are you nervous walking around some of these towers?

A: Definitely my chosen route does not go exactly under one of these really tall buildings, especially when there is already a known issue in one of them, in a particular building.

This interview has been edited for length and clarity.

With files from the Calgary Eyeopener