53 Pa. Stat. § 24944
Above the proscenium opening there shall be an iron girder covered with fire-proof materials to protect it from the heat. There shall also be constructed a relieving arch over the same, the intervening space being filled in with hard burnt brick of the full thickness of the proscenium wall. Should there be constructed an orchestra over the stage, above the proscenium opening, the said orchestra shall be placed on the auditorium side of the proscenium fire wall and shall be entered only from the auditorium side of said wall. The moulded frame around the proscenium opening shall be formed entirely of fireproof materials, and if metal be used the metal shall be filled in solid with noncombustible material and securely anchored to the wall with iron. The proscenium opening shall be provided with a fireproof metal curtain or a curtain of asbestos or similar fireproof material, approved by the bureau of building inspection, sliding at each end within iron grooves securely fastened to the brick wall and extending into such grooves not less than six inches on each side. Said fire-proof curtain shall be raised at the commencement of each performance and lowered at the close of said performance, and be operated by approved machinery for that purpose. The proscenium curtains shall be placed at least three feet distant from the foot-lights at the nearest point.
53 P.S. § 24944