Representatives from the National Transportation Safety Board on Friday joined the investigation into a massive chemical spill that sent dozens of people to the hospital in north suburban Beach Park the day before.
The NTSB sent a team of four people to Beach Park Thursday, the agency tweeted, with on-scene investigation into the hazardous materials release beginning Friday morning.
The NTSB's lead investigator was expected to speak during a news conference alongside the Lake County sheriff's office Friday beginning at around 1 p.m.
More than three dozen people, including firefighters and police officers, were taken to area hospitals after a cloud of anhydrous ammonia spilled into the sky from a tractor trailer at around 4:30 a.m. Thursday morning.
The chemical spill took place at the intersection of North Green Bay Road and East 29th Street, with authorities issuing a shelter-in-place order for those within a one-mile radius of the spill for several hours as crews remained on the scene. The incident also forced several area schools to close for the day over safety concerns and transportation issues.
Thirty-seven people, seven of which were in critical but stable condition, were taken to hospitals for breathing and inhalation issues, authorities said. The remaining 30 were said to be in serious but stable condition. Among those hospitalized were 11 firefighters and three police officers, the Lake County Sheriff's office reported.
Police arrived at the scene early Thursday morning after a caller reported a possible vehicle fire at the intersection.
"As the deputies approached they were overcome by the chemical that was in the air," Sgt. Christopher Covelli with the Lake County Sheriff's office said. "They had to retreat and couldn’t actively attend to the scene."
The driver of the vehicle also appeared to have "some medical issues" likely due to the spill, he added.
Anhydrous ammonia is a colorless gas with "pungent, suffocating fumes," per the CDC, which said it can cause difficulty breathing, chest pain, burns and more, becoming potentially fatal at high concentrations.
"This is a very dangerous chemical that can cause unconsciousness and worse case scenario death," Covelli said.
It was not immediately clear what caused the tractor trailer to begin spilling the chemical. Authorities were expected to details "investigative protocol" at Friday's news conference.