DENVER — Energy companies, local governments and advocacy groups on Monday will debate proposed new rules for thousands of oil and gas pipelines in Colorado after a fatal explosion last year blamed on leaking gas. The Colorado Oil and Gas Conservation Commission opens two days of hearings on regulations for installing, testing and shutting down flow lines, which carry oil, gas and wastewater from wells to tanks and other nearby equipment. The rules are in response to an April 17 explosion in the town of Firestone that killed two people, injured a third and destroyed a house.