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HOUSTON (CBSMiami) – Two explosions rocked a chemical plant north of Houston overnight, raising concerns that smoke from the fires could be toxic.

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Flames were still burning Thursday morning at a disabled Arkema Inc. plant in Crosby, Texas. Flooding from Tropical Storm Harvey knocked out refrigeration units that were cooling volatile chemicals.

“We heard some popping noise coming from that area, then gray smoke, followed by a fire,” said Assistant Harris County Fire Chief Bob Royall.

The plant had been evacuated earlier in the week and a mile and a half perimeter was set up around it. Thursday morning 15 first responders on this scene were treated for smoke inhalation.

“This event had been expected and planned. They were different organic peroxides, of different grades, that were released and that created a ‘pop’ in the containers where they were being stored. Some gray smoke initially came from it and that eventually turned into black smoke,” said Sheriff Ed Gonzalez. “It is not anything toxic, it is not anything we feel is a danger.”

The sheriff’s office says area residents are not in any danger but admit more explosions are possible.

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“So far what has happened is exactly what we expected,” said Royall.

Harvey has finally left area, but has left behind a growing crisis in East Texas.

The city of Beaumont lost its water supply overnight and is beginning to evacuate one hospital. The city of Port Arthur is still mostly under water.

“If you call 911 and we havent gotten there yet, we are on the way,” said Port Arthur Mayor Derrick Freeman. “If you see someone making a rescue in your neighborhood, please flag them down.”

There is still plenty of flooding in Houston and thousands remain in shelters but the city is working to get back on its feet. Some buses and trains are running and both airports are open again.

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The confirmed death toll from Harvey is now 31 and is expected to rise.