A crack in a tank holding a toxic chemical may have helped avert an explosion or bigger leak, as evacuation orders begin to lift.

California officials have lifted the final remaining evacuation orders in Orange County after securing a chemical tank leak, allowing Garden Grove residents to return to their homes after a week of nerves over the possibility of a spill or explosion.

About 40,000 people are under evacuation orders and schools have shut down in Southern California due to a hazardous chemical leak.

An official said there's no active leak, but evacuations orders are to prepare for either a spill or an explosion from a failing chemical tank.

A dangerous chemical leak that forced nearly 50,000 people from their homes in Orange County, California, may have taken a hopeful turn after crews discovered what officials described as a pressure-relieving crack in the leaking industrial tank.

The risk of a catastrophic explosion of a damaged chemical tank Southern California has been eliminated following a close overnight inspection that confirmed a crack in the tank has relieved pressure and cooled the chemical.

Two emerging factors may be helping reduce the risk of a catastrophic explosion at the chemical tank in Garden Grove, California.