A class action lawsuit of Mon Valley residents will allege that a 2018 fire at a U.S. Steel site resulted in spiking emissions, noxious odors and physical discomforts.

Allegheny County Court Judge Philip Ignelzi on Friday issued an order certifying a class of more than 123,000 Mon Valley residents in the environmental case against U.S. Steel.

The class action suit seeks compensation as the result of the December 2018 fire at U.S. Steel’s Clairton Coke Works.

The gas-fueled fire burned for about two hours and tore through the plant’s No. 2 Control Room, damaging critical equipment used to clean coke oven gas and shutting down pollution-control systems. The Allegheny County Health Department subsequently began to warn residents about high levels of sulfur dioxide, and a 2021 Pitt study said the fire sickened nearby residents.

The plaintiffs in the case claim U.S. Steel should have prevented the fire, which they allege originated from a series of mechanical failures caused by long-term corrosion and inadequate maintenance.

They allege the resulting emissions caused noxious odors and physical discomforts — including burning throat, watering eyes, headaches, nausea and difficulty breathing — among Mon Valley residents.

The court certified the case as a class action, meaning all 123,000 Mon Valley residents’ nuisance claims can be addressed in a single lawsuit.

The court at this point did not rule on the merits of the allegations against U.S. Steel. It ruled only on whether class action is proper for this situation.

In an emailed statement, U.S. Steel spokesperson Amanda Malkowski said the company was reviewing the judge’s opinion.

“Environmental stewardship is a core value at U.S. Steel, and we remain committed to the safety of our employees and the communities where we live and work,” she said.

Malkowski declined to offer additional comment on the pending litigation.

Sarah Siskind of Miner, Barnhill & Galland, the plaintiffs’ lead attorney, said she was “thrilled” by the court’s decision to move ahead with a class action suit.

“Now we can move forward and hold U.S. Steel accountable to its Mon Valley neighbors,” she said.

Julia Felton is a Tribune-Review staff writer. You can contact Julia by email at jfelton@triblive.com or via Twitter .