The height of the roof varies with the depth of the product in the tank.
Workers climb a ladder to the top of the tank and down an internal ladder to the roof.
Is there an exemption from the confined space standard for utility workers. The caller asked for help in interpreting the definition of a confined space. Each space is a filter plenum that measures approximately 40 x 40 x 20 feet. The only means of entry or exit is the submarine style door that is an airlock. It allows upright entry, but requires 15-20 pounds of pressure to open because of the negative pressure in the space.