A workplace incident last week claimed the lives of two part-time package handlers at the UPS operation in Ontario, California.

News reports say 20-year-old Austin Stache and 22-year-old Noe Tinoco Jr. were killed in the incident, which occurred early in the morning of Nov. 25 at the UPS hub at Ontario International Airport.

A Cal/OSHA spokesman said the victims were on a “tug” when it flipped over, crushing them. A tug pulls dollies full of containers that are to be loaded onto airplanes.

UPS reportedly has supervisors give a safety reminder to employees before every shift.

Capacity at the facility – at which packages are sorted for distribution via ground and air- was doubled in a 2016 expansion.

Cal-OSHA is investigating the incident.