A smoke barrier may or may not have a fire resistance rating. Smoke barriers may have openings that are protected by automatic closing devices, adequate to inhibit movement of smoke through the opening. The smoke barrier may be constructed of heat-strengthened or tempered glazing or the equivalent and protected by sprinkler heads constructed in accordance with subchapter seventeen of this chapter and installed a maximum of six feet (6'-0") on center on each side of the barrier. If the smoke barrier is constructed of glass, the portions of the smoke barrier located within two feet of the door opening and within five feet of the floor shall be constructed of tempered glass. Glass panels having an area in excess of nine square feet with the bottom edge less than eighteen inches above the floor shall likewise be constructed of tempered glass. Portions of glass smoke barriers shall be marked where required in accordance with the rules of the board of standards and appeals.