Step 1: DO NOT take the elevator down to the parking garage!!! One of the fatalities from Allison happen because of that. From the Houston Chronicle article:

"The woman went down in the elevator after a broadcast was made in the building by the security department that water was coming into the parking garage and anyone in the building should go down and move their cars," Hurst said.

The woman, who was the only elevator occupant at the time, drowned when water rushed into the elevator while on the third level of the garage, Hurst said.

"It appears that water began rushing into the elevator and it malfunctioned and she drowned in the elevator," Hurst said. "She didn't even make it to her car parked on the fourth level."

-Blast