A man is in a fatal condition with internal burn injuries as well as injuries to the face and neck after being burned by an explosion at work.
He and the other three were part of the staff in the building when it exploded on Thursday afternoon.
Explosion caused it to be so strong that some of the ceiling sheets and other chemicals in the workshop were scattered 50 meters away.
The incident occurred at Richbay Chemicals in Boksburg.
William Ntladi of Ekurhuleni Emergency Services said factory factories were already burning when he arrived at the scene. He said the explosion could be seen from afar and that some of the factory's 210-liter containers had escaped through the roof.
"The company is dealing with a variety of corrosive chemicals and they do not know what they are, but there are various containers from 5 liters to 1000 liters.
"The report said the chemical caused a fire," Ntladi said.
He was wounded by three other people who were not injured by the fire and were burned by corrosive chemicals.