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Several materials were considered for the sprayed thermal insulation. The exterior columns required insulation not only for fire protection but also to control column temperatures under service conditions.Alcoa recommended for the exterior columns the use of a sprayed material produced by U.S. Mineral Products, Co. known as CAFCO BLAZE-SHIELD Type D. The same material was eventually selected for the floor trusses and core beams and columns. This product, however, contained asbestos fibers. On April 13, 1970, New York City issued restrictions on the application of sprayed thermal insulation containing asbestos. The use of CAFCO BLAZE-SHIELD Type D was discontinued in 1970 at the 38th floor of WTC 1. The asbestos-containing material was subsequently encapsulated with a sprayed material that provided a hard coating. A green dye was added to the encapsulating material so that the asbestos containing SFRM could be identified. Thermal protection of the remaining floors of WTC 1 and all of WTC 2 was carried out using CAFCO BLAZE-SHIELD Type DC/F, a product that contained mineral wool (glassy fibers) in place of the crystalline asbestos fibers. On the basis of tests, it was reported that Executive Summary Draft for Public Comment xxxvi NIST NCSTAR 1-6A, WTC Investigation the thermal properties of CAFCO Type DC/F were equal to or “slightly better” than those of CAFCO Type D.