Upon an apache detecting the player or when the Xenian Tentacle escapes from the site.
The large tentacle has broken out of the facility at Exit B. The HECU is trying to combat it... with no success. Looks like they are pulling out and commencing an airstrike.
If the Alpha Warheads are disabled, the HECU will return to Exit B and kill us. But, if left active, the airstrike has been called and the surface is destroyed with you in it.