Regulators set to decide on crude-by-rail shipping rules are relying on testing methods that may understate the explosive risk of the crude, according to a growing chorus of industry and Canadian officials. The tests’ accuracy is central to addressing the safety of growing crude-by-rail shipments across the continent: whether Bakken crude contains potentially dangerous levels of dissolved gases. Several trains carrying Bakken crude have exploded after derailing, including a fiery accident last year that killed 47 people in a small town in Quebec. The North Dakota Industrial Commission is expected to rule Thursday on what steps, if any, producers must take to strip volatile gases out of crude oil before loading it into railroad tank cars. The regulator’s decision will be based, at least in part, on the testimony of a half-dozen oil executives who urged the state to consider the conclusions of a study by the North Dakota Petroleum Council, a lobbying group for energy producers. That study found Bakken crude was no more volatile than other so-called light crudes commonplace in Texas and elsewhere.