Hampshire-based Hydro Pumps Ltd had been subcontracted in the summer of 2007 to cut away concrete top sections of the support columns on the bridge to allow engineers to replace worn out support bearings.
On 26 July a 27 year-old employee was using a hand-held jet gun that delivered a high-pressure concentrated stream of water at a 5mm distance from the surface of the concrete. 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.
Work was suspended for a few days pending an internal investigation. But within 10 minutes of it resuming on 1 August the replacement operative 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.
Dundee Sheriff Court heard last week that Hydro Pumps had modified the gun by shortening its lance to a length less than recommended by the manufacturers and industry guidance. Employees were operating the gun at almost twice the force recommended by industry guidance. The company failed to provide a safe system of work, failed to provide and maintain safe equipment, and failed to supervise the use of appropriate protective equipment.
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."