A damaged chemical tank in Southern California may have cracked, potentially lowering the risk of a catastrophic explosion, though evacuation orders remain in effect for about 50,000 residents.

Firefighters have found a potential crack in the massive tank filled with a toxic chemical at risk of explosion in Southern California.

“No one has ever had this situation before because the chemical is so volatile,” said TJ McGovern, the interim fire chief of the Orange County Fire Authority, who called the situation “unprecedented.”