FIREPROOFING. This term is applied to methods of making normally combustible materials fireproof as far as may be, but in practice the most that can be done with them is to subdue or retard inflammability. The subject is one of great im portance, especially in connection with the construction of the atres and other buildings where large numbers of people are col lected together and where special illumination is required. The nature of or disposition of materials used in theatres has become the subject of public regulation in many countries and it is usual to provide that no combustible scenery shall be employed unless it has been treated with flame-retarding solutions. The London County Council regulations, for instance, provide that in the atres materials such as wood, canvas, textiles, etc., must be ren dered non-inflammable by impregnating them with solutions, and names the following as having been found suitable :—( ) for scenery and coarse fabrics : a solution of 1 lb. of phosphate of ammonia and 2 lb. chloride of ammonia (sal ammoniac) in 12 gal. water ; for delicate fabrics and cotton wool: io oz. borax and 8 oz. boracic acid in i gal. of water. Stage wood work must be thoroughly impregnated with phosphate of am monia. It is, however, quite impossible to make wood-work really fireproof and the council therefore insist, as far as possible, upon the use of incombustible materials such as asbestos.
Such precautions have only been taken in recent times, the London County Council's regulation requiring stage wood-work to be rendered non-inflammable having first come into force in 1901. In 1923 special conditions were laid down with regard to the use of plywood, and at the present time (19 28) the con struction of theatres is governed by a long series of safety regu lations which experience has shown to be necessary. Floors, tiers and roofs, fittings in dressing rooms, all floors and linings to scene stores, workshops, etc., have to be formed of fire-resisting material ; soft wood or other inflammable wall linings, decora tions, partitions, screens or barriers must not be used, and cavities must not be left behind any linings or decorations. No fire-place may be used and no heating system involving use of a naked flame may be installed in any portion of the auditorium or stage ; the stage and cellars below must not be congested with scenery and properties, and the regulations do not stop at fireproofing. There are stringent rules as to hydrants, fire appliances, fire drills, light installations, etc., and it is required that a competent fireman with practical experience in fire prevention and extinction should be on the staff. (A. F. H.) United States.—The building code recommended by the Na tional Board of Fire Underwriters is commonly used as a basis in the preparation of building ordinances of many cities. A solution which has been widely recognized for the fireproofing of fabrics, is one made of three parts of ammonium phosphate, two parts of ammonium chlorate and one part of ammonium sulphate and about 4o parts of water. Lumber impregnated with fire-retardant chemicals is termed "fireproof wood." The industry had its begin ning in the United States in 1895. The principal market for fireproof wood has been in New York city. Its building code prohibits the use of wood for floors and interior trim for build ings in excess of 15o ft. in height unless fireproofed in accordance with rules prescribed by the superintendent. The treatment of the wood is commonly done by impregnating it with fire-retard ant chemicals in closed cylinders under artificial pressure. (See TIMBER PRESERVATION.) (C. T. B.)