Clive Dainty was working at Filtration Service Engineering Ltd in Kidderminster when a 335-litre vessel exploded as it was being pressure tested, Worcester Crown Court was told.
The extent of the explosion tore the two parts of the vessel apart, with one part hitting 51-year-old Mr Dainty and forcing him into a cabinet against a wall.
Health and Safety Executive inspectors likened his injuries to those sustained on the battlefield as they described the vessel exploding like a 'bomb'.
Mr Dainty, from Kidderminster, was hospitalised for several months and had to have both legs amputated.
He also suffered head injuries and has severely restricted movement in his arms, which have been repaired with metal plates.
The force of the blast also threw a fire extinguisher through a nearby wooden staircase.
The incident happened on December 8, 2011.
An investigation by the Health and Safety Executive found that the company was testing the vessel as there were concerns about the quality of the welding. However, instead of simply filling it with water, the firm decided to use compressed air.
The court was told that the factory's compressed air supply was directly connected to one of the vessel's openings.
A valve, which could be manually opened and closed, and a pressure gauge were installed, and the vessel filled with compressed air.
The pressure built up to such an extent that eventually the vessel exploded.
Filtration Service Engineering Ltd, which is based at Oldington Trading Estate, Kidderminster, was fined £30,000 at Worcester Crown Court on Thursday. The firm was also ordered to pay £15,325 in costs after pleading guilty to breaching health and safety regulations.
Following the court hearing, HSE inspector Ed Fryer said: "The injuries sustained in this incident were more akin to those sustained on a battlefield.
"The vessel exploded like a bomb during the course of a normal working day, and everyone in the factory was at risk from the operation because no measures were put in place to protect them.
"Pneumatic testing is a dangerous activity and significant planning is required to ensure the risks are managed.
"The management of health and safety in this factory was woefully inadequate and simple measures could have been implemented to prevent the incident from happening.
"An assessment of the risks involved in pneumatic pressure testing should have identified that air was not a suitable testing medium.
"The test could have been carried out by simply filling the vessel with water.
"It is a miracle that more people were not injured and that nobody lost their life," he added.
Bosses from Filtration Service Engineering Ltd declined to comment about the incident following the court case.