dnc

Interesting question, we have similar issues in my workplace. I do not think an H and S angle will win the day for you. We have had a mixture of both patterns for the last 10 years or so - generally speaking most prefer 2 days 2 nights as they do not have to do 4 nights in a row, but some prefer 4 days 4 nghts as they refer to the 2 day 2 night pattern as a '5 on, 3 off' pattern as you always finish on nights.

Horses for courses really but, as I said, I do not think H and S arguments will be clear cut for the reasons mentioned above. As someone managing people on these shifts, the 4 day 4 night shift gives more options for covering sickness/holdays, so that may be why your employer wants to change.
DNC