New Delhi, May 25 -- A damaged chemical tank in Southern California cracked over the weekend, which authorities were hopeful would relieve pressure and reduce the risk of an explosion.

Some 50,000 residents in Garden Grove, a city of roughly 170,000 about 40 miles (60 kilometers) south of downtown Los Angeles, have been evacuated and are waiting for a resolution. The tank overheated Thursday and began venting vapors, leaving local and state officials scrambling to evade a worst possible scenario at the aerospace company site.

No injuries have been reported.

Fire officials planned to send in a team overnight to determine if the pressure has been relieved, which would reduce the worst-case scenario of an explosion, Orange County Fire Aut...