Two sanitation workers were injured, one critically, when a trash truck exploded in Wilmington, Delaware Thursday morning.

The workers were loading trash onto the truck a little after 7 a.m. on Vandever Avenue when the truck started compressing the trash, which prompted the blast, the Wilmington Police Department said in a news release.

Right before the explosion, the men had noticed some sort of tank in the truck, the WPD said. According to police, the blast happened just as the compressor came down on the tank.

The explosion caused one of the workers, a 40-year-old man, to suffer a chest wound. He was airlifted to the hospital. The man was conscious and alert when paramedics arrived and is listed in critical condition with non-life threatening injuries, police said.

The other worker, a 42-year-old man, was taken to the hospital via ambulance with minor injuries.

Police continue to investigate the incident.