The train dispatcher is afraid that engaging the mechanical emergency brake would generate enough heat to set off explosive gases. In fact, the course of action he selects has a much greater chance of triggering an explosion by [1] sparks routinely generated by the subway's third rail power shoe, [2] the dynamic brake system he proposes to use turns kinetic energy into heat through banks of resistors, and [3] directing Nolan Wood to make an impromptu shunt is sure to create sparks.