A method of and system for producing Class-A fire-protected oriented strand board (OSB) sheets. Each Class-A fire-protected OSB sheet has: a core medium layer made of wood pump, binder and/or adhesive materials; a pair of OSB layers bonded to the core medium layer; a clean fire inhibiting chemical (CFIC) coating on the surface of each OSB layer, made from CFIC liquid applied to the surface by dipping the OSB sheet into the CFIC liquid in a dipping tank, allowing shallow surface absorption into the OSB layers and ends of the core medium layer at atmospheric pressure; and a moisture, fire and UV protection coating spray coated over the CFIC coating to provide protection against moisture, fire and UV radiation from Sunlight, which is quickly dried by passing through a drying tunnel on the production line.