Oxford Plastics makes a range of site safety products including barriers, cones and traffic signs.
The fire broke out at the firm’s unit near Ennstone Airfield in Oxfordshire.
Twelve workers were on site at the time and one was taken to hospital suffering from smoke inhalation after being rescued by a colleague.
A spark during welding work is believed to have caused the blaze.
A spokesman for Oxford Fire and Rescue said: “The fire developed very quickly and one man got trapped and he was rescued by a colleague who managed to force his way into that part of the building.
“The chap who was trapped inhaled a lot of smoke and his colleague probably saved his life.
“He was taken to hospital after breathing in smoke but I have been told that he is going to be okay.
“Firefighters had to wear breathing apparatus masks because of the toxic smoke and our main concern was preventing the fire from spreading to an adjacent paper mill, which we managed to do.”