Two people were killed in a car crash at Interstate 55 and Butler Hill Road Tuesday, after they stopped due to a traffic tie-up caused by a hazmat spill on the interstate.

A man and woman from Florissant were rear-ended by a pickup truck about 2:50 p.m. as they were standing in stopped traffic on the interstate, which pushed their car into a semi truck also waiting for traffic. The investigation of the crash shut down the interstate through the evening rush hour.

Driver Patricia Callaghan, 71, and her passenger John Callaghan, 82, both of Florissant, died in the crash, the Missouri State Highway Patrol reported.

John Callaghan was taken to Mercy Hospital South by an ambulance from the Mehlville Protection District, where he later died. Patricia Callaghan was pronounced dead at the scene at 3:01 p.m. by MFPD paramedics. John Callaghan died at Mercy South at 3:30 p.m.

The driver of the truck that hit the Callaghans, Anthony Leopold, 30, of Barnhart, had minor injuries and was also taken to Mercy South by MFPD ambulance.

The Callaghans’ car, a 2013 Nissan Cube, was stopped due to traffic in the fifth and sixth lanes on northbound Interstate 55, the MSHP said in a crash report.

Leopold came up behind the stopped traffic in his 2011 Ford F-150 in the second lane. He changed lanes to the right and hit the Callaghans’ Nissan from behind, spinning it and forcing it into the driver’s side of the semi, which was driven by Oleksandr Voytouych, 52, of Harwood Heights, Illinois. Voytouych had no injuries.

All the drivers and passengers involved were wearing seat belts.

Hazmat spill tied up traffic

The Callaghans were waiting in traffic caused by a hazmat spill that shut down most of the lanes of the interstate while Mehlville Fire and other first responders worked to clean it up.

An alarm came in around noon reporting that a small liquid chemical leak had happened on the ramp from southbound I-55 onto northbound I-270.

The leak happened when a 1-cubic-yard shipping container inside a tractor-trailer shifted during transport and failed.

About 100 gallons of the “mildly corrosive substance,” which is used to control or kill the growth of bacteria, spilled onto the highway. The spill was contained using sand and an absorbent material similar to cat litter.

The St. Louis County Hazardous Material Team responded to help control the spill.

The MFPD was on the scene from noon to soon after the fatal crash, when the scene was turned over to the Missouri Department of Transportation.

During the three hours responding to the spill, MFPD responded to three crashes on the interstate, including the crash on 55.