There have been six pipeline incidents involving hydrogen sulphide that meet Level 3 criteria — the highest — in British Columbia in the past three years, a spokeswoman for the B.C. Oil and Gas Commission said Tuesday.

Those six incidents include the two recent explosions along pipelines in the Dawson Creek area, which police have said appear to have been deliberately set.

The commission defined a Level 3 emergency as something that may contain one or all of the following factors:

• At the time of the incident a danger exists to the public or environment.
• Control of the situation has been lost (i.e. rare occasion of a well blowout).
• Release of hazardous substance.
• Extensive involvement of external emergency services, federal and/or provincial agencies.
• Emergency extends beyond company property.

Bomb experts have been combing the area of the two latest explosions all week, but answers are still few and far between.

The two explosions were along sour gas pipelines owned by EnCana Corp. near Dawson Creek, near the B.C.-Alberta boundary.

Police believe the Dawson Creek attacks are related to a letter sent to local media demanding a stop to oil and gas operations.

The explosions also have revealed a measure of discontent among residents whose quiet rural life has been interrupted by pipelines, wells and a bustling industry that has seen massive expansion in just a few years.

Commission spokeswoman Lee Shanks said in a statement that all incidents at oil and gas facilities in the province are reported to the commission, which tracks everything from tipped-over water containers at a well site to gas leaks and fires.

The commission also said that pipelines are built with emergency shutdown valves installed at pre-set points along the pipeline.

If the valves detect a pressure drop in the pipeline, they close automatically, stopping the flow of gas through the pipeline and trapping the gas between the valves closest to the rupture. This limits the volume of gas that can escape.

Other safeguards include the provision that prior to development or operation, sites containing H2S (hydrogen sulphide) must have an emergency planning zone determined and an emergency response plan established.