series of accidents -v- process: case law?

I’m looking for case law on this with a view to seeking leave to appeal a first tier tribunal decision. 

For many years the appellant operated a particular machine on a factory production line.  The machine was operated 20 x per hour, 40 hours per week.

In 1999 the machine was changed. The new one was very stiff and heavy to operate, causing increasing shoulder pain.  On one occasion there was specific incident where sudden and severe pain was experienced.  However the appellant worked on for a further 4 weeks.  The factory then shut down for a week or so for the summer.  Upon return the appellant immediately found he was in too much pain to use the machine and was assigned to various lighter roles around the factory before eventually being dismissed.

So, he operated the dodgy machine approximately 4,800 times over a 6 week period, but perhaps this needs to be put into the context of the nearly 40,000 such operations per year?

He has had several IIDB awards (each time by appealing successfully to the first tier tribunal) but his latest appeal has been turned down on the basis that the pain and loss of function still experienced is due to process, not the one off incident, which medical evidence concurs would have long since got better.  But is this process, or can it be argued that it is a series of approx 4,800 tiny accidents (and one major one)?