“In case of fire, use elevators.”

It sounds like apostasy, as if a lifetime’s indoctrination had suddenly been invalidated.

But it is exactly the instruction that office workers in New York’s tallest skyscrapers may receive in coming years. The Fire, Buildings and City Planning Departments are writing rules to govern what are called occupant-evacuation elevators — cars that can, in special circumstances, be used to move people down in an emergency.

That would upend decades of codes and practices based on the notion that elevators are perilous and undependable in fires or other emergencies. Experts who have spent years studying building evacuations believe that approach has become outmoded and is in itself potentially dangerous as extremely tall skyscrapers increasingly pierce the New York skyline.

“We have to find a better way to evacuate people from high-rise buildings, including people with disabilities,” Edward T. Ferrier, the deputy assistant chief of fire prevention, said. He added that the Fire Department’s attitude about occupant-evacuation elevators was “positive.” Though there are none in New York, they have been installed in a number of towers overseas.