Seven shuttle astronauts, two faking injuries, completed an emergency launch pad evacuation Wednesday after a make-believe fire and explosion in a major test of post-Challenger safety improvements.

The "emergency egress simulation" began with the astronauts and launch technicians in the launch pad "white room" at the end of an access arm that would butt up against a shuttle's hatch before launch. The shuttle Discovery, on tap for blastoff this summer, will not be mounted on the pad until June.The test ended shortly after 11:30 a.m. when nine people faking injuries, including two astronaut stand-ins, were airlifted to area hospitals.

"Everything went well," according to a NASA spokeswoman.

Since Challenger's destruction in January 1986, launch pad 39B has been equipped with more fire detectors along with fire-blocking plates protecting steel mesh decking. A new underground bunker has been built at the base of the pad, and procedures have been streamlined to improve efficiency and safety.

As the crew was in the process of pretending to board the imaginary shuttle, a smoke bomb on the pad gantry was set off about 8:58 a.m., emergency water deluge systems began drenching the gantry structure and the "emergency" began.

Participating in the exercise were rookie astronauts Frank Culbertson Jr., Kenneth Cameron, Kathryn Thornton, Charles "Sam" Gemar, David Low, Pierre Thuot and Jay Apt.

NASA spokeswoman Lisa Malone reported a make-believe fire on the gantry level below the astronauts and later said an explosion was simulated as firefighters battled the fake flames.

The access arm is located at the 195-foot level of the launch pad. In an emergency requiring a fast exit, elevators could prove dangerous or inoperative and for that reason, "slidewire baskets" are anchored on one side of the gantry attached to 1,200-foot cables stretching away to the ground below.

In a real crisis, up to 21 astronauts and pad technicians could jump in the baskets for a dizzying 50-mph ride to the ground where they could either enter a new reinforced underground bunker or climb aboard an armored personnel carrier for a speedy exit.

For Wednesday's test, however, the astronauts and rescue personnel rode elevators to the ground while the baskets made the trip loaded with sand bags. Once on the ground, the astronauts climbed back in and proceed from there as if they had just arrived.

Only five baskets were available at the time of the Challenger accident, but two more have been added and all seven now feature protective blankets to shield against flame.