Dundee Sheriff Court heard that Hampshire based Hydro Pumps Ltd had been subcontracted to cut away concrete top sections of the support columns on the Tay Road Bridge bridge to allow engineers to replace worn out support bearings.
On 26 July 2007 a 27 year-old employee was using a hand-held jet gun that delivered a high-pressure concentrated stream of water.
He suddenly slipped and fell losing his grip on the gun.
He toppled forward as he had been balancing himself against the force generated by the gun and the water jet penetrated into his abdomen.
Due to his severe injuries he has been unable to return to work since.
The work was suspended pending an internal investigation.
But within ten minutes of it resuming on August 1 a second employee, who had been brought in to replace the first, was himself seriously injured when the same gun came apart in his hands and he lost control of it, resulting in the water jet shooting into his knee.
He was taken to hospital with severe leg injuries but despite two operations to try and save his leg, it needed to be amputated.
Hydro Pumps Ltd, of Fareham, Hampshire, pleaded guilty to safety breaches and was fined £46,500.
Following the case, HSE Inspector Gerry McCulloch, said: “These tragic and almost identical incidents could easily have been avoided had Hydro Pumps Ltd identified the risks associated with this kind of work and implemented appropriate risk-reduction measures.
“The first incident should have been a clear wake-up call that the water jetting was unsafe but little changed and it was only ten minutes after Hydro Pumps Ltd had restarted the job that the second man was injured.
“Two workers suffered severe and life-changing injuries, the effects of which are still felt today and will be for the foreseeable future.”