A series of rail accidents involving oil tank cars that exceed federal safety standards yet still burst into flames after derailing is shifting the focus from the container to the crude — and whether it’s too explosive to be carried by train. A wreck over the weekend in Canada brought the total to four in less than a month in the U.S. and Canada. All involved relatively modern tank cars known as the CPC-1232, which are designed to be sturdier than a model that regulators have said are prone to rupture. Safety advocates say the spills show that a proposed rule now under review at the White House to require even tougher tank cars is necessary, but that it may not go far enough. “The problem is in the product,” said Phil Steck, a New York state assemblyman whose district near Albany is bisected by oil trains. […]