In the wake of several recent efforts by environmental activists to disrupt service on company high-pressure pipelines carrying tar-sands products, Calgary-based Enbridge Inc. is taking measures to strengthen the security of its pipelines.

"We are assessing and employing various additional, permanent measures to enhance our security and safety at these sites to help prevent these types of tampering activities in the future. As part of ensuring the effectiveness of these measures, we will not provide details or discuss them publicly," said Graham White, a spokesman Enbridge Inc.

This past December in Sarnia, Ontario a number of Canadians opposed to the transport of hazardous materials in pipelines managed to get to the other side of a fence protecting the pipelines and then locked themselves on to a wheel controlling the flow.

While the incident caused no injuries or significant service disruptions, the owner of the pipeline — the newly reversed and expanded Line 9 between southwestern Ontario and Montreal — said that incident and others have raised "serious concerns."

Martin Rudner, professor emeritus at Carleton University who is an expert in security and critical infrastructure, said the industry has a variety of measures in place to secure their sites and respond when they are breached — and generally they seem to be working.

"It's hard to make an overall judgment, but I think the best way to judge it is the fact that no major interruption has taken place," he said.