1.   Another is a missing or improperly installed vent line that is supposed to connect each fixture to the main vent stack.

2.   Another possibility under investigation is that a fire traveled into the center tank from a vent line that runs all the way down both wings.

3.   Efforts to start the mission Thursday were scrubbed when a cloud of highly flammable hydrogen fuel vapors leaked from a vent line.

4.   Efforts to repair the leaking vent line by patching what engineers identified as a crack in an old weld seam were under way late Thursday.

5.   Flames were then blasted through a vent line into the center tanks, causing the explosion, according to this theory.

6.   Flames were then blasted through a vent line into the center tanks, causing the explosion.

7.   He monitors his temperature gauges, adjusting the heat by alternate use of his burners and a cooling vent line.

8.   Officials said the leak occurred in a vent line outside the shuttle, at the base of the launch platform.

9.   The launch platform on which the vent line is located dates back to the Apollo program.