Scotmod. What part of 7671 are you quoting on this?
Previously I have run mains cabling and fire alarm/ELV/data in the same tray but with a divider to separate them. This was agreed by everyone and signed off by the Clients consultant.
in the NON-mains side, I was under the impression that the voltages in fire alarm, data and security (Power Over Ethernet - in our case) were so low that they would not cause any interference with each other.
This has always been a grey area in 5839. I think a lot of older generations do not agree with running fire alarm and data together!