Whenever hazardous materials (water-reactive materials, acid-reactive materials, and air-reactive materials) are processed or stored, signs with letters not less than 3 inches high on contrasting background stating, “WATER- REACTIVE MATERIAL,” “ACID-REACTIVE MATERIAL,” and/or “AIR-REACTIVE MATERIAL,” appropriately identifying that type of hazard or hazards involved, shall be posted at any location inside a building and at any location within an area outside a building where such materials are stored or processed, and at such other locations as may be required by the Chief.