Mists of tear gas may cloud downtown Calgary if police and protesters clash during the June G-8 summit, but City Hall will remain almost impenetrable to airborne chemicals.
A city spokesman said officials made certain of that this week, completing work to ensure the air intakes to the City Hall complex can be shut in seconds if the surrounding air becomes contaminated.
"We've installed an emergency shut-down switch for the ventilation system for the complex," said Glenn Gibb, the city's manager of facility operations for corporate properties.
"It was just a way of preventing (chemicals or tear gas) from getting into all the air intakes and being distributed throughout the building."
A series of huge grilles -- each about three metres by five metres -- sit atop the buildings that comprise City Hall, four on the roof of the municipal building, two above the administration building and one over the central atrium. Another intake serves the city hall print shop and one at the loading dock serves the plaza.
A ground-level intake between the administration building and the old City Hall provides air to the offices and other rooms of the turn-of-the-century sandstone building.
About 18,000 cubic metres of outside air can flow through the intakes each minute, to be heated or cooled, depending on the season, and mixed with air already circulating inside the complex.
The intakes and their fans can now be shut by computer, Gibb said, and while the permanent modification does not make City Hall airtight, it will largely protect people inside from fumes.
"With the atrium, there's such a huge volume of air, there'd be plenty of oxygen," Gibb said, though he admitted stopping air flow would have one drawback.
"It may get a bit warm," he said, "(but) it may take an hour to two hours before it started to get really warm."
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