Before excavation begins, locate and identify utility services such as electrical, gas, steam, water, and sewer in the area. Any danger to workers from these utility services must be eliminated or controlled. Pointed tools cannot be used to probe for underground gas and electrical services. If possible, blunt shovels should be used to expose the facility. Take caution especially if newer, sharper spade shovels are used. Trees, utility poles, rocks, or similar objects near the edge of an excavation must be removed or secured to prevent workers from being injured. Excavation work must be carried out in accordance with the written instructions of a professional engineer or professional geoscientist when The excavation is more than 6 m (20 ft.) deep, OR Support structures other than those specified in the regulation are used in the excavation, OR An improvement or structure adjacent to the excavation could endanger workers, OR The excavation is subject to vibration or hydrostatic (water) pressure A professional engineer’s plan and written instructions to support or slope the sides of the excavation must include information on the subsurface conditions expected to be encountered. A copy of the plan and any written instructions—signed and sealed by the engineer—must be available at the site.