Tragedy struck six years ago, when a toddler was killed by a large piece of metal hurtling down from a highrise construction site in Calgary.

The debris was thrown from the building by high winds. It was the impetus for creating a wind warning system for the city of Calgary that is mandatory for any contractor building higher than five storeys in the downtown or Beltline.

"It can be extremely dangerous. Wind can be very unpredictable and quite extreme, especially at height," said Frederick Vine, co-chair of the city's on-site safety committee. He works with EllisDon construction and helped create the warning system. 

"So the advanced weather forecasting system is specifically designed to work at site-specific locations in the downtown and Beltline area, as well as at specific heights."

Specific forecasting

RWDI Consulting, which created the system, modelled the city of Calgary and inputs weather information from several sources to forecast high winds.

"They [contractors] would get an alert through their computer or on their phone, and that alert would tell them that there's danger and they would look at it and find out exactly what the alert was," said Vine.

Sites can then secure materials on the construction site to ensure another tragedy does not occur. There are times when cranes can't operate and rare occasions when all work has to stop.

The following list shows examples of certain types of debris at risk of being lifted by winds from 10 to 120-plus km/h:

  • six to 12 km/h - ball of crumpled paper, tarp
  • 21 - 30 km/h - 2-inch pPolystyrene rigid insulation 
  • 31 - 40 km/h = R-12 Insulation, single sheet; 3/8" plywood sheet; steel stud
  • 41 - 50 km/h - sheet metal, aAluminum, 20 gauge;  half-inch pPlywood sheet; teel stud, half-inch diameter plastic pipe
  • 75 - 89 km/h - half-inch nut, scaffolding, five-eighth-inch drywall sheet, plastic pipe/donduit, four-inch diameter 
  • 120-plus km/h - two-inch nut, three-inch long bolt 

Accuracy

"It also can be very accurate. There a have been lots of opportunities where the alerts have come out and everyone's looking and saying it's a nice blue, clear sky and why would this alert happen," said Vine. "Then all of a sudden, two hours later, the wind is extreme."

Vine says there have been "almost no incidences of debris falling off sites that have been recorded by the city of Calgary" this year.

The system is paid for through fees collected in the permit process.