Detroit - An acrid smell hangs in the air at Trenton Forging Co on the outskirts of Detroit as a two-tonne hammer slams a bar of red hot steel with enough force to shake the building.

A worker uses tongs to position the piece, heated to 2200 degrees, under the hammer, then onto a conveyor belt. The process is repeated 7000 times a day at the 90-employee plant, resulting in fuel rails that feed gasoline to injectors.

But the days of forging fuel rails is numbered. They're among hundreds of parts in internal combustion engines that won't be needed when the world transitions to electric vehicles, a fact that isn't lost on Dane Moxlow, the vice president of Trenton Forging, whose grandfather started the business in 1967.

"This might go away completely," Moxlow, 33, said as a pair of workers behind him inspected a freshly made rail. "Is it something we worry about? Yeah. But it's also something we plan for."

Across the US, thousands of companies such as Trenton Forging are warily eyeing a future of electric vehicles that contain a fraction of the parts of their petrol-powered counterparts and require less servicing and no fossil fuels or corn-based ethanol. It's a transition that will be felt well beyond Detroit, as millions of workers at repair shops, fuel stations, oil fields and farms find their jobs affected by an economic dislocation of historic proportions.