#	Letters of Interpretation
1	10/01/1991 - 1926.650 - Manufacturer's Tabulated Data in the design and application of trench safety systems.
2	07/01/2010 - 1926.650(b) - Can a person who qualifies as a "competent" person under one section of support P also qualify as a competent designer of structural ramps under 1926.651(c)(1)(i)?.
3	09/30/2004 - 1926.650 - Permissibility of using average excavation depth to determine protective system requirements for the excavation.
4	12/22/2003 - 1926.650(b) - Registered professional engineer approval requirements for combination trench shield and sloping system trenches with a depth greater than 20 feet.
5	01/16/2003 - 1926.650 - Registered professional engineer approval requirements for manufactured trench protection systems deeper than 20 feet.
6	09/21/2001 - 1926.650 - Clarification of utility "owner" as used in the Safety and Health Standards for Excavations, Underground Installations.
7	08/10/2000 - 1926.650 - Trench shield must extend 18" above excavation walls when below grade.
8	10/29/1991 - 1926.650 - Stacking trench boxes in trenches.
9	10/01/1991 - 1926.650 - Classification and subsequent designs may be used if they have been approved by a registered professional engineer.
10	06/05/1991 - 1926.650 - Testing of type C soil is not necessary if employees are adequately protected.