Incidents like Cape Ray blasting mishap deemed rare

A close call for a Cape Ray family earlier this week is a very rare occurrence in the construction industry, says a blasting expert.

Engineer says correct placement of blasting mats, amount of explosives is critical

A nearly seven-kilogram rock crashed through the kitchen ceiling of the Wall family home in Cape Ray this week, missing Aiden Wall by mere centimetres. (Colleen Connors/CBC)

A close call for a Cape Ray family on Newfoundland and Labrador's southwest coast earlier this week, during blasting operations, is a very rare occurrence in the construction industry.

Rock-breaking expert Ben Hammoud said incidents like the one in Cape Ray typically only occur when heavy recycled tire mats are incorrectly placed over the blast site or when too many explosives are used.

"You want the rock to move because that's the point of the blasting — to fragment and heave the rock — but you want that body of rock to remain on site and not go on adjacent properties," Hammoud said. He works with an Ontario firm called DST Consulting Engineers, which provides advice to construction companies that carry out blasting operations.

An investigation is now underway to determine how the rock could have travelled the roughly half-a-kilometre distance from the blast site. (Colleen Connors/CBC)

He said it's actually safer to break rock with explosives than by mechanical means.

"When controlled and done properly, blasting is very safe," Hammoud said during an interview with the Corner Brook Morning Show.

Blasting operations suspended

Such reassurance is cold comfort to the Wall family in Cape Ray.

Their home was damaged and Aiden Wall,18, barely escaped injury late Monday afternoon when a seven-kilogram rock crashed through the roof and landed on the floor, not far from their dining-room table.

It's believed the rock came from a blast that occurred about a quarter-of-a-kilometre away.

The work is related to the construction of the Maritime link, which will carry electricity from Newfoundland and Labrador to Nova Scotia.

Blasting operations have now been suspended while an investigation is completed.

Mammoud said so-called "fly rock" incidents are not unheard of, but are very rare.

Blasting mats key to controlled explosion

So what makes for a safe blast?

Mammoud said it's essential to determine the correct amount of explosives, and this is linked to the type of rock being broken.

And in order for it to be a controlled explosion, blasting mats weighing about a tonne each are required.

He said a backhoe typically places the mats in a pre-determined pattern, depending on how the workers want the rock to move.

He said the mats also minimize the noise of the blast, which is important in populated areas.

He said the direction of the blast is also controlled by the angle of the blast holes, and the time delay between each charge.

He said there are rare occasions when a blast will "backfire," with the energy from the blast moving in the opposite direction.

If this is not anticipated and the mat coverage is inadequate, fly rock incidents can occur.

"It's not a very good experience," he explained.

With files from Lindsay Bird

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