Excavation Safety (Don’t dig your own grave!)

1. Excavation Safety(Don’t dig your own grave!)

2. Objectives • To provide students with: • An introduction to 29 CFR 1926, • Subpart P-Excavation Standard • An overview of soil mechanics • An introduction to trenching and excavation hazard recognition

3. Data On Excavation Cave-in Injuries • BLS Data Shows That Each Year • Approximately 1000 Injuries Occur • Decreasing Trend Over Time • Of These, • 140 result in permanent disability • 75 result in death • 1% of all occupational fatalities

4. OSHA’s Response • Regional Emphasis Program in late ’70’s • National Emphasis Program of 9/1985 • CPL 2.69 National Program Directive • Inspection Conducted When; • Receive employee complaint • CSHO observation • Receipt of referral • Ask employer to voluntarily abate • If employer will not voluntarily comply, then call the “OSHA Duty Officer” • Compliance Assistance

5. Mechanics Of Trench Injuries • Mechanisms of energy transfer • Struck-by • Force is dependent upon amount of materiel falling and fall distance • Caught between • 850 pounds of force applied against the chest • Causes slow, agonizing asphyxiation

6. Multiple Cave-in Scenario Surface subsides Tension crack Over-stressed unconfined trench wall Vertical stresses due to weight of column of soil

7. Multiple Cave-in Scenario First Cave-in Trench wall ready to collapse a second time at any moment Additional tension cracks Debris from first cave-in First cave-in

8. Multiple Cave-in Scenario Second Cave-in Trench wall ready to collapse a third time at any moment Second cave-in Debris from first and second cave-ins

9. Multiple Cave-in Scenario Third Cave-in Debris from first, second and third cave-ins Third cave-in

10. SLOPE ZONE FAILURE SOFT ZONE STABLE STABLE SLOPE FAILURE SOFT WEAK ZONE

11. Rotational Failure POCKETS SAND POCKETS

12. SLOUGHING Sloughing (Air Drying) Wedge Failure

13. Effects of Water Surface Runoff Ground Water Stable Ground Soft Saturated Zone Water Accumulation

14. Fractured Rock Stable Un-Stable

15. Previously Disturbed Areas Spoil Old Utility Trench (Crossing Utility) Native Soil Tension Cracks Bedding Material Old Utility Trench (Parallel Utility)

16. Footing “B”: An engineer should be consulted A B Utility: Look for a block failure Utility Line Footing “A”: Standard practice can be followed Failure Zone NOTE 1: Slope shall be determined by soil classification Type A = 3/4:1 Type B = 1:1 Type C = 1 1/2:1

17. Other Excavation Hazards • Cave-ins are perhaps the most feared trenching hazard. But other potentially fatal hazards exist, including asphyxiation due to lack of oxygen in a confined space, inhalation of toxic fumes, drowning, etc. Electrocution or explosions can occur when workers contact underground utilities.

18. OSHA Standards Related to Excavations and Trenching:29 CFR 1926, Subpart P • 1926.650 • Scope, application, and definitions applicable to this subpart • 1926.651 • General requirements • 1926.652 • Requirements for protective systems

19. 1926.650 Scope & application, definitions • Accepted engineering practices • Aluminum hydraulic shoring • Bell-bottom pier • Benching • Cave-in • Competent person • Cross braces • Excavation • Faces or sides • Failure • Hazardous atmospheres` • Kick-out • Protective systems • Ramp • Registered professional engineer • Sheeting • Shield • Shoring • Sloping • Stable rock • Structural ramp • Trench

20. Competent person • Specific training in, and be knowledgeable about, • soils analysis • the use of protective systems • requirements of this standard • Preamble page 45909 • And have the authority to take corrective action

21. Definitions • "Excavation" means any man-made cut, cavity, trench, or depression in an earth surface, formed by earth removal. • "Trench (Trench excavation)" means a narrow excavation (in relation to its length) made below the surface of the ground. In general, the depth is greater than the width, but the width of a trench (measured at the bottom) is not greater than 15 feet (4.6 m). If forms or other structures are installed or constructed in an excavation so as to reduce the dimension measured from the forms or structure to the side of the excavation to 15 feet (4.6 m) or less (measured at the bottom of the excavation), the excavation is also considered to be a trench.

22. 1926.651 - General requirements • Surface encumbrances • Underground installations • Access and egress • Exposure to vehicular traffic • Exposure to falling loads • Warning system for mobile equipment • Hazardous atmospheres • Protection from hazards associated with water accumulation • Stability of adjacent structure • Protection of employees from loose rock or soil • Inspections • Fall protection

23. 1926.651(c)(2) Means of egress • Means of egress from trench excavations. A stairway, ladder, ramp or other safe means of egress shall be located in trench excavations that are 4 feet (1.22 mm) or more in depth so as to require no more than 25 feet (7.62 m) of lateral travel for employees.

24. 1926.651(k)-Inspections • Daily inspections of excavations, the adjacent areas, and protective systems shall be made by a competent person for evidence of a situation that could result in possible cave-ins, indications of failure of protective systems, hazardous atmospheres, or other hazardous conditions. • An inspection shall be conducted by the competent person prior to the start of work and as needed throughout the shift. Inspections shall also be made after every rainstorm or other hazard increasing occurrence. These inspections are only required when employee exposure can be reasonably anticipated.

25. 1926.652 - Requirements for protective systems • Protection of employees in excavations • Design of sloping and benching systems • Design of support systems, shield systems, and other protective systems • Materials and equipment • Installation and removal

26. 1926.652 (a)-Protection of employees in excavations • (1) Each employee in an excavation shall be protected from cave-ins by an adequate protective system designed in accordance with paragraph (b) or (c) of this section except when: • (i) Excavations are made entirely in stable rock; or • (ii) Excavations are less than 5 feet (1.52 m) in depth and examination of the ground by a competent person provides no indication of a potential cave-in.

27. Sloping RequirementsAre Based Upon Soil Type • Rock • Type A soil • Type B soil • Type C soil Note that sloping requirement is based upon “worst layer” soil classification

28. Protective Systems • Shoring • Trench Box

29. Worker Protection Systems • Appendix A • Soil Classification • Appendix B • Sloping & Benching • Appendix C • Timber Shoring • Appendix D • Aluminum Hydraulic Shoring

30. Soil Classification Definitions • Type A - Most stable: clay, silty clay, and hardpan (resists penetration). No soil is Type A if it is fissured, is subject to vibration of any type, has previously been disturbed, or has seeping water. • Type B - Medium stability: silt, sandy loam, medium clay and unstable dry rock; previously disturbed soils unless otherwise classified as Type C; soils that meet the requirements of Type A soil but are fissured or subject to vibration. • Type C - Least stable: gravel, loamy sand, soft clay, submerged soil or dense, heavy unstable rock, and soil from which water is freely seeping. • Layered geological strata (where soils are configured in layers) - The soil must be classified on the basis of the soil classification of the weakest soil layer. Each layer may be classified individually if a more stable layer lies below a less stable layer, i.e. where a Type C soil rests on top of stable rock. • STABLE ROCK is natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed. It is usually identified by a rock name such as granite or sandstone. Determining whether a deposit is of this type may be difficult unless it is known whether cracks exist and whether or not the cracks run into or away from the excavation.

31. Hazard Recognition Slides