Some 60 years ago, lumps of wet, grey material were given to students in art classes to shape and mould into art to proudly display at home. It was especially good for objets d'art such as candle holders, since the substance was famous for stopping the spread of flames.

That material was asbestos, now known as a toxic material for which there is, quite simply, no safe level of exposure.

It's still regularly found in older schools and universities across Canada, wrapped around pipes, above ceilings and behind walls.

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Though asbestos is the biggest workplace killer in the country, Health Canada is committed to the position that it's only an issue when fibres become airborne and "significant quantities" are inhaled or ingested. While the Canadian government maintains it has "consistently acted to protect Canadians from the health risks of asbestos," dozens of countries – including Britain, Australia, Japan, Sweden, Germany and Denmark – have banned it outright in recognition of the fact that exposure to fibres can cause various diseases, including mesothelioma and other cancers.

The World Health Organization has declared all forms of asbestos carcinogenic and recommends its use be eliminated; the International Agency for Research on Cancer has said there is no safe form of asbestos, nor is there a threshold level of exposure that is risk-free.

In Canada, many cash-strapped schools and universities follow Health Canada's position that asbestos is safe if contained – abatement is wrapped into other renovation and repair projects, and teachers and staff are taught how to prevent accidental exposure. But despite the best of intentions, accidental exposure happens.

Dr. Patricia Martens – a senior research scientist at the University of Manitoba's Manitoba Centre for Health Policy, professor in its Faculty of Medicine and recipient of the Order of Canada – knows this first-hand.

In the fall of 2012, she thought she had an especially stubborn summer cold or, worst case, that she'd picked up tuberculosis doing First Nations community research (TB is particularly prevalent among First Nations).

"It felt like I had pneumonia … but it just kept getting worse and worse so I could barely breathe and I felt like I was drowning all the time. So then they sent me to specialists in January and that's when they did the biopsy and came up with this bizarre ruling," Martens said.

The incurable mesothelioma diagnosis was staggering, especially considering that a colleague had recently died of mesothelioma.

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"I'm very realistic. I might live a few more weeks, I might live a few more months, I might live another year. But I've already outlasted the median time from diagnosis, which is around a year. So I'm grateful for every day," Martens says.

And as a public-health expert, she has a message: Her illness was entirely preventable at a policy and legislation level. "I don't want anybody to be intentionally or unintentionally exposed."

Her accidental exposure came as a University of Manitoba student, she believes, in the huge dining-exam room in which she ate her lunch every day. It had an open-slat ceiling with beautifully finished wood – and asbestos filling stuffed in the gaps.

Laura Lozanski, a former nurse and the occupational health and safety officer for the Canadian Association of University Teachers, questions the Canadian government's position that asbestos is safe when it is enclosed behind walls and ceilings.

"All you have to do is knock a chair into the wall if it's got asbestos, even though it's intact [and] it's never been disturbed … now it's been disturbed. That's all it takes," she said.

Across the country, accidental exposure occurs time and again:

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In British Columbia, the New Westminster School District was fined for failing to inform workers that the floor in a classroom they were tearing up in 2005 contained the toxic material.

The school board in Algoma, Ont., temporarily shut down a school in 2006 after a teacher and a group of students accidentally disturbed asbestos tiles.

In 2012, a Kawartha Lakes, Ont., elementary teachers' union filed a complaint against the Trillium Lakelands District School Board for allegedly failing to inform staff and students at Bracebridge's Monck Public School about asbestos-containing ceiling tiles in some of its classrooms.

And in April, the auditorium at St. Patrick Catholic Secondary School in Toronto was temporarily closed after tests of its air ducts found asbestos in six out of 18 samples.

The Toronto District School Board (TDSB) is Canada's biggest with some 250,000 students and almost 600 schools. Of those, a majority of schools "are older, so they would have some sort of asbestos present to varying degrees, whether it be a ceiling, or maybe their pipes are wrapped," said spokesman Ryan Bird.

Despite that, there's no plan to proactively remove asbestos.

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"If you don't need to remove it because it's not a danger to anyone, then why spend thousands to hundreds of thousands of dollars to remove it," said Chris Broadbent, TDSB health and safety manager. "As long as it's undisturbed, it's not an issue."

That approach is echoed in the city's Catholic board, with 90,000 students, as well.

"Don't redecorate, just leave everything alone, just leave the ceilings alone, leave the walls alone, even in new buildings," said Corrado Maltese, the Catholic board's manager of health and safety. He confirmed asbestos is present in 172 of the Catholic board's 201 schools.

As part of efforts begun in 2010 to upgrade 168 schools for full-day kindergarten, the Catholic board has spent about $15,000 to $20,000 per school removing asbestos.

While funding is always an issue, another cash-strapped public institution has taken a markedly different approach to abatement: The Toronto Transit Commission has spent about $40-million since 1982 removing asbestos from behind subway-tunnel liners, a dangerous and time-consuming after-hours process that is 90-per-cent complete.

"The TTC, where appropriate, takes proactive measures to protect its workers, customers and environment," said Brad Ross, the TTC's executive director of communications.

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Without government regulation at any level banning the substance, it's up to individual, publicly elected school boards to determine where asbestos abatement fits into overall budgets.

At the very least, the Elementary Teachers' Federation of Ontario wants the province to follow Saskatchewan's lead and introduce a mandatory public registry for asbestos in public buildings. (While Toronto's Catholic board makes publicly available online locations of asbestos in its schools, the TDSB doesn't allow public access to its asbestos records.)

"[Asbestos is] a known carcinogen, and asbestos-related disease has been confirmed in a limited number of cases involving education workers," said Sam Hammond, president of the elementary teachers' union.

"I don't want anybody to ever have to experience this lethal form of cancer that you really can do very little about – and was totally man-made," Patricia Martens said. "I want the [Stephen] Harper government to come up with a statement saying that all forms of asbestos is dangerous for human health. We really need to take a deep, hard gulp and say, we've got to do something … so that nobody else is going to be exposed."

With files from Tavia Grant