Columbia, Mo. ? The University of Missouri has reopened a campus building where four researchers were injured by a gas explosion.

School officials said this week that Schweitzer Hall is structurally sound and safe for researchers to return. The 98-year-old building houses the university’s biochemistry department.

Monday’s hydrogen and nitrogen gas explosion injured a graduate student, a research scientist and two postdoctoral fellows. Three were treated and released Monday. The fourth remained Tuesday in good condition at University Hospital.

The third-floor laboratory where the explosion occurred will be rebuilt.