The Allegheny County Health Department has formally requested to join a federal lawsuit against U.S. Steel.

Earlier this week the National Environmental Law Center filed the suit on behalf of its clients, the Clean Air Council and PennEnvironment. The complaint is based on air quality violations related to a December 24 fire at the Clairton Coke Works facility.

“Our legal counsel determined that collaborating with the citizens’ groups would increase the resources available to the department and allow for the best possible outcome of our enforcement action for public health and impacted residents,” said county health department director Dr. Karen Hacker in a press release.

WESA reported earlier this week that under its Clean Air Act permits, U.S. Steel’s Clairton Plant is required to run the gas that comes out of its coke ovens through pollution controls. The Christmas Eve fire knocked out that part of the plant; instead of shutting down operations or going on idle, U.S. Steel sent its unfiltered gases to flares at Clairton and two other nearby plants.

The lawsuit says that put the people who live near the plants at risk from toxic air pollution.

Pollution controls that were damaged by the fire have been back in place since early April. But plaintiffs argue that these violations were avoidable and that similiar violations likely will happen again if the court doesn't intercede.

The Clairton facility is the largest coke plant in the country. Coke is a key component in steel making; it's created by baking coal at very high tempatures.