What we know about the chemical tank incident in Southern California — and what questions still linger

U.S. newsWhat we know about the chemical tank incident in Southern California — and what questions still lingerOfficials said Monday that the worst-case scenario, a massive explosion, had been averted. But it’s unclear how the emergency started in the first place.Listen to this article with a free account00:0000:00Add NBC News to GoogleRisk of explosion has been ‘eliminated’ in California toxic chemical tank incident02:39Get more newsLiveonShareAdd NBC News to GoogleMay 25, 2026, 4:13 PM EDTBy Aria BendixWhat sent a chemical storage tank in Garden Grove, California, to the verge of either leaking or blowing up? And how did authorities avoid the worst-case scenario — a massive vapor explosion that threatened to destroy buildings and expose residents to toxic plumes? Subscribe to read this story ad-free Get unlimited access to ad-free articles and exclusive content.Over the last several days, Southern California officials — with help from state and federal agencies — have tried to avert what they feared could be one of the worst chemical incidents in California history. The emergency has forced officials to explain complicated chemistry dynamics to concerned residents who evacuated their homes with no scheduled return date.At issue is a storage tank at an aerospace facility containing approximately 7,000 gallons of liquid methyl methacrylate, a chemical used to manufacture resins and plastics. The Orange County Fire Department reported late last week that the tank had begun to heat up and bulge.That meant one of two horrifying scenarios: Either the pressure in the tank would get so high that it would crack and the chemical would spill out, or the tank would rupture and the chemical would vaporize and explode. Experts feared the blast would cause two nearby tanks of methyl methacrylate to explode as well. “That was what we were handed — a leaking tank or a tank that blows up,” Craig Covey, an Orange County Fire Authority division chief, said Friday.Exposure to methyl m...