| Underwriters Laboratories Standard For Safety Fire Tests of Window Assemblies UL9-6th edition 1994. |
| Underwriters Laboratories File R13412 Apr. 29, 1988 Project 88 NK5046 Karpen Steel Products Weaverville, N.C. |
| Underwriters Laboratories File R4373 Mar. 5, 1993 Project 92RT3965 Karpen Steel Products Weaverville, N.C. |
| Underwriters Laboratories File R4373 Mar. 4, 1993 Project 92 RT 3964 Karpen Steel Products Weaverville, N.C. |
| Underwriters Laboratories File R4373 Feb. 1, 1996 Project 95 RT 7610 Karpen Steel Products Weaverville, N.C. |