Turns out Enbridge has been hiding a flaw in its gas meter/vent system. If your vent is cover by snow and the pressure increases inside the furnace because it cannot properly vent and the furnace starts up and it will cause the pressurized gas to explode. My Dad said an Orleans woman died last year and her 20 yr old daughter lost her legs in this type of  blast. The Ottawa fire department inspector was quoted as saying t he blast was causes by the covered air vent..and Enbridge claims their vent/meter system was not at fault but is trying to settle the matter out of court. So check your furnace air vents!!