A federal panel that analyzed the collapse of the World Trade Center towers after the Sept. 11, 2001, terrorist attacks suggested Thursday that the creation of fireproof and structurally hardened elevators could provide the best way to evacuate people quickly from skyscrapers and transport emergency workers to upper floors.

That was among the 30 recommendations contained in a report that calls for the revision of safety standards used in the construction and maintenance of U.S. skyscrapers.

The three-year study released by the National Institute of Standards and Technology (NIST) recommends that all office towers have emergency plans that include strategies for full evacuations. At present, emergency plans require only anticipation of partial evacuation.

Building designs should include wider emergency stairwells, and elevators should be situated at a distance from each other so that some will function if others are damaged, the study said. The panel called for uniform standards for testing the effects of wind and fire on building skeletons.

"There is no recommendation that is going to be a silver bullet. It's a collection of recommendations that are going to make occupants and first responders safer in future disasters," said S. Shyam Sunder, lead investigator on the panel.

Sunder said the proposed measures are not intended to protect against the impact of an airplane slamming into a building. Rather, the report focuses on potential hazards such as tornadoes, fires, earthquakes and hurricanes, as well as terrorist attacks.

Safety standards and building codes are determined by state and local officials. The recommendations, NIST investigators said, are meant to influence and inform their policy decisions. NIST will launch an Internet-based system to track the response to its suggestions by code-making agencies.

If adopted, the changes could increase the cost of construction by 5 percent or more in high-priced real estate markets, according to investigators.

The final report did not include any new conclusions about the cause of the World Trade Center's collapse. Earlier reports said that the impact of the aircraft dislodged fireproofing, allowing flames to spread faster and weakening the building.