(Bloomberg) -- A chemical leak that killed two people and hospitalized 30 at a LyondellBasell Industries NV plant near Houston is under investigation.

The incident at LyondellBasell’s complex in suburban LaPorte that began Tuesday evening is over and air-monitoring indicates “no levels of concern,” the company said in a statement. Federal and state regulators have been alerted and LyondellBasell said it’s probing the cause.

The deadly leak came less than a week after a separate chemical spill at a nearby Dow Inc. plant that prompted evacuations and an order for residents to remain indoors and shut off air conditioners to avoid the pollution. As recently as late 2018, the Lyondellbassell facility was penalized for “high-priority” violations by the U.S. Environmental Protection Agency.

Of the 30 injured workers, six remained hospitalized as of late morning local time, LyondellBasell said.

The leak occurred in the plant’s acetyles unit, which produces chemicals including glacial acetic acid and vinyl acetate monomer that are used as raw materials for making paints, films and textiles. This acetyles unit had been shut earlier Tuesday for planned maintenance.

(Updates with hospitalization status in fourth paragraph.)

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