ST. LOUIS (AP) — Authorities say three people have been killed in a boiler explosion in a building in an industrial area of south St. Louis.

The St. Louis Fire Department reported on Twitter that four other people also were injured, two critically, in the blast shortly before 8 a.m. Monday at the Loy-Lange Box Co.

Fire officials say at least three buildings have been damaged by debris.

Federal workplace safety regulators say a St. Louis company whose boiler exploded causing at least three deaths Monday has paid fines for workplace violations three times since 2014.

Scott Allen of the Occupational Safety and Health Administration says the Loy-Lange Box Co. paid a $3,741 fine after an August 2016 inspection found holes in floors that prevented proper cleaning.

An inspection in November 2014 found defective equipment, including a forklift without lights and damage to some safety latches. The company paid $6,566.

And in February 2014, the company paid $2,450 for defective energy control procedures, such as not properly training employees to ensure machinery was turned off and powered down.

Three people died and four were injured when the Loy-Lange boiler exploded, launching parts of it through the roofs of two nearby buildings. It's not clear if any of the earlier safety violations involved the boiler.