A pallet rack beam pair is just two rails, nothing stops a pallet from tipping into the aisle, and nothing stops small items from falling through to the level below. Wire decking closes that gap: a welded wire mesh panel that drops onto the beam flanges and turns an open bay into a flat, load-rated surface, without blocking sprinkler coverage or airflow the way a solid deck would.
Because it's open mesh, wire decking is standard practice for anywhere fire code, ventilation, or visibility matters, the deck holds the load while light, HVAC, and fire suppression all still pass straight through it.