[Code of Federal Regulations] [Title 30, Volume 1] [Revised as of July 1, 2006] From the U.S. Government Printing Office via GPO Access [CITE: 30CFR27.38] [Page 156] TITLE 30--MINERAL RESOURCES CHAPTER I--MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR PART 27_METHANE-MONITORING SYSTEMS--Table of Contents Subpart C_Test Requirements Sec. 27.38 Tests to determine adequacy of windows and lenses. Impact tests. A 4-pound cylindrical weight with a one-inch diameter hemispherical striking surface will be dropped (free fall) to strike the window or lens in its mounting or the equivalent thereof at or near the center. At least three out of four samples shall withstand the impact according to the following table: ------------------------------------------------------------------------ Height Overall lens diameter (inches) of fall (inches) ------------------------------------------------------------------------ Less than 4................................................... 6 4 to 5........................................................ 9 5 to 6........................................................ 15 Greater than 6................................................ 24 ------------------------------------------------------------------------ Lenses or windows of smaller diameter than 1 inch may be tested by alternate methods at the discretion of MSHA.