Portable fire extinguishers having a gross weight not exceeding 40 pounds shall be installed so that the top of the extinguisher is not more than 5 feet above the floor. Extinguishers having a gross weight greater than 40 pounds (except wheeled type) shall be so installed that the top of the extinguisher is not more than 3 1/2 feet above the floor. In no case shall the clearance between the bottom of the extinguisher and the floor be less than 4 inches.