Sprinkler locations are based on coverage area, which depends on the types of heads and their heights above or distances from whatever is to be protected. If you install cable trays that block part of the coverage pattern, you defeat the effectiveness of the fire protection in that area. Technically, that is a Code violation. We always recommend “basket-type” tray to minimize interference, but if it’s full of cable, it might as well be solid.
A Fire Protection Engineer should examine any revisions to layout, including the addition of cable trays, to ensure that you are still protected. Simply dumping water into the room will not suppress a fire, particularly in the relatively congested environment of a Data Center. Unfortunately, the fire protection system is often overlooked once it is installed. It should be re-examined when re-arranging cabinets, expanding an existing room, adapting a former mainframe room, or even when adding anything overhead like cable trays. Even if the fire protection system was originally designed correctly, any significant change defeat its effectiveness. This is true with gas-type fire protection systems as well.