OSHA only requires that extinguishers be mounted, located, and identified so that they are readily accessible. However, NFPA 10, Standard for Portable Fire Extinguishers, states that units weighing 40 pounds or less be installed such that the top of the unit is not more than five feet above the floor. For units weighing more than 40 pounds, the top of the unit should be no more than 3.5 feet above the floor. There should always be at least four inches between the bottom of the unit and the floor.