Office of Safety & Health Consultation presents Excavations & Trenching Objectives In this course, we will discuss the following: • Excavations/Trenching: Subpart P – 1926.650 - Scope, application, and definitions applicable to this subpart – 1926.651 - Specific excavation requirements – 1926.652 - Requirements for protective systems 1926 Subpart P Subpart and Standard 1926. Number of Serious Violations – FY 2013 3 Subpart P - Appendices • Appendix A - Soil Classification • Appendix B - Sloping and Benching • Appendix C - Timber Shoring for Trenches • Appendix D - Aluminum Hydraulic Shoring • Appendix E - Alternatives to Timber Shoring • Appendix F - Selection of Protective Systems 1926 Subpart P Definitions • Excavation – Man-made cut, cavity, trench, or depression formed by earth removal. • Trench – Narrow excavation – Depth is greater than the width, but not wider than 15 feet. • Shield – Structure able to withstand a cave-in and protect employees. 1926.650(b) Definitions • Shoring – Structure that supports the sides of an excavation and protects against cave-ins. • Sloping – Technique that employs a specific angle of incline on the sides of the excavation. 1926.650(b) Definitions • Competent person – Must have specific training in and be knowledgeable about: • Soils classification • Use of protective systems • Requirements of the standard – Must be capable of identifying hazards, and authorized to eliminate them. 1926.650(b) Weight of Soil • Weight of soil varies with type and moisture content. • One cubic foot weighs 110 pounds to 140 pounds. • One cubic yard (27 cubic feet) of soil can weigh more than 3,000 pounds. Excavation Hazards • Cave-ins are the greatest risk. • Other hazards include: – Asphyxiation due to lack of oxygen – Inhalation of toxic materials/fumes – Fire – Machinery moving near edge of excavation causing a collapse – Severing underground utility lines – Falls Injury and Death • Excavating is one of the most hazardous construction operations. • Most accidents occur in trenches 5-15 feet deep. • Usually no warning before a cave-in. Specific Excavation Requirements • • • • • • • (a) Surface encumbrances (b) Underground installations (c) Access and egress (d) Exposure to vehicular traffic (e) Exposure to falling loads (f) Warning system for mobile equipment (g) Hazardous atmospheres Specific Excavation Requirements • (h) Protection from hazards associated with water accumulation • (i) Stability of adjacent structures • (j) Protection of employees from loose rock or soil • (k) Inspections • (l) Fall protection Surface Encumbrances • All surface encumbrances that create a hazard to employees must be removed or supported to safeguard employees. 1926.651(a) Underground Installations • Estimated location of utility installations [sewer, telephone, fuel, electric, water lines] must be determined prior to opening an excavation. 1926.651(b)(1) Underground Installations • When utility companies or owners cannot respond to request to locate underground utility installations within 24 hours. – Employer may proceed with caution, provided detection equipment, etc. is used to locate utility installations. 1926.651(b)(2) Underground Installations • Exact location of underground installations must be determined by safe and acceptable means. 1926.651(b)(3) Underground Installations 1926.651(b)(3) Underground Installations 1926.651(b)(3) Underground Installations • Underground installations must be protected, supported or removed as necessary to safeguard employees. 1926.651(b)(4) Structural Ramps • Structural ramps used for access or egress of equipment must be designed by a competent person. 1926.651(c)(1)(i) Egress - Trench Excavation • Stairway, ladder, ramp, or other safe means of egress must be located in trench. • Required if trench 4 feet or more in depth. • Lateral travel distance no more than 25 feet. 1926.651(c)(2) Egress - Trench Excavation 25 feet 25 feet Ramp, ladder or stairs required at 4 feet or deeper. 1926.651(c)(2) Egress - Trench Excavation 1926.651(c)(2) 1926.651(c)(2) Egress - Trench Excavation • Is this correct? Exposure to Vehicle Traffic • Employees exposed to public vehicular traffic must wear warning vests or other suitable garments marked with or made or reflectorized or high-visibility material. 1926.651(d) Exposure to Falling Loads • Employees must not be permitted to work under loads handled by lifting or digging equipment. 1926.651(e) Exposure to Falling Loads • Stand away from equipment that is being loaded or unloaded. • Equipment operators may stay in their equipment during loading and unloading if equipment has proper cab shield or canopy. 1926.651(e) Warning System - Mobile Equipment • Mobile equipment operated adjacent to excavation and operator cannot see edge of the excavation: – Warning system must be utilized. • Barricades • Hand or mechanical signals • Stop logs 1926.651(f) Warning System - Mobile Equipment Is this correct? 1926.651(f) Hazardous Atmospheres • Testing conducted before employees enter the trench and regularly thereafter. 1926.651(g)(1) Hazardous Atmospheres • Less than 19.5% or more than 23.5% oxygen • A combustible gas concentration greater than 20% of the Lower Flammable Limit (LFL) • Concentrations of hazardous substances that exceed OSHA’s Permissible Exposure Limits (PEL) 1926.651(g)(1) Hazardous Atmospheres • Test at 4 feet if suspected – LEL – Oxygen – CO – H2S – Petroleum – Other toxics 1926.651(g)(1) Emergency Rescue Equipment 1926.651(g)(2)(i) Emergency Rescue Equipment • Emergency rescue equipment must be readily available where hazardous atmospheric conditions exist or expected to develop during work. – Breathing apparatus – Safety harness and line – Basket stretcher 1926.651(g)(2)(i) Water Accumulation • Employees must not work in excavations where there is accumulated water, or where water is accumulating. • Unless precautions taken to protect workers: – Water removal to control level of water – Special support or shield systems 1926.651(h)(1) Water Accumulation 1926.651(h)(1) Water Accumulation • Water removal equipment and operations must be monitored by a competent person to ensure proper operation. 1926.651(h)(2) Water Accumulation • Excavations subject to runoff from heavy rains require an inspection by a competent person. 1926.651(h)(3) Well Points Used to Remove Ground Water What are the Hazards? What are the hazards? Stability of Adjacent Buildings • Support systems such as shoring, bracing, or underpinning must be provided to ensure stability of structures. 1926.651(i)(1) Stability of Adjacent Structures • Excavation below the foundation that could pose a hazard shall not be permitted except: • ‘ – Underpinning provided – Stable rock – Registered professional engineer (RPE) has approved 1926.651(i)(2) Underpinning Underpinning to prevent structural failure. 1926.651(i)(2)(i) Stability of Adjacent Structures • Sidewalks, pavements and appurtenant structure must not be undermined unless supported to protect employees from collapse of such structures. 1926.651(i)(3) Protection of Employees • Adequate protection provided to protect employees from loose rock or soil that could pose a hazard by falling or rolling from an excavation face. 1926.651(j)(1) Potential Problems Extra load from spoil pile Fissures Belly bulge Protection of Employees • Employees must be protected from equipment or materials that could fall or roll into excavations. – Materials and equipment must be kept 2 feet from edge of excavation or use retaining devices. 1926.651(j)(2) Rule: 2 Feet 1926.651(j)(2) Two Feet From Edge 1926.651(j)(2) Extra Surface Loading 1. What’s the Hazard? 2. See it now… Inspections – Competent Person • Daily and before the start of each shift. • As dictated by the work being done in the trench. • After every rain storm and other events that could increase hazards, e.g., snowstorm, windstorm, thaw, earthquake, etc. 1926.651(k)(1) Inspections • Frequency of testing should be increased if equipment is operating in trench as well as if welding, cutting, or burning is done in trench. 1926.651(k)(1) Fall Protection • Walkways provided when crossing over excavation. • Standard guardrail installed when more than 6 feet above a lower level. 1926.651(l)(1) Protection of Employees • Employees in an excavation must be protected from cave-ins by adequate protective system. – Except when: • Made entirely in stable rock • Excavation is less than 5 feet deep and examined by competent person 1926.652(a)(1) Sliding Toppling Tension Crack Bulging Heaving or Squeezing Soil Weight Soil Weight Methods of Protection • Sloping and benching • Shoring (spaced sheeting, closed sheeting) • Trench shield • Other occasionally used systems 1926.652 Protective Systems • Protective systems shall have capacity to resist without failure all loads applied or transmitted to the system. 1926.652(a)(2) Installation and Removal • Support systems must be installed and removed in a manner that protects employees from cave-ins. 1926.652(e)(1)(ii) Installation and Removal • Removal must begin at, and progress from, the bottom of the excavation. • Members released slowly to note any indication of possible failure of remaining members. 1926.652(e)(1)(V) Installation and Removal • Excavations of material to a level not greater than 2 feet below the bottom of the support system or shield must not be permitted. 1926.652(e)(2)(i) and (g)(2) Deadly Trench Collapse What’s the hazard? What’s the hazard? What’s the hazard? What’s the hazard? What’s the hazard? What’s the hazard? What’s the hazard? Soil Classification • Contains definitions • Sets forth requirements • Describes acceptable visual and manual test for use in classifying soils Appendix A Definitions • Cohesive soil – Clay, or soil with a high clay content, which has cohesive strength – Does not crumble – Can be excavated with vertical side slopes – Plastic when moist – Hard to break up when dry Soil types Appendix A Definitions • Granular soil – Gravel, sand, or silt, with little or no clay content – No cohesive strength – Cannot be molded when moist – Crumbles easily when dry Note: Some moist granular soils exhibit apparent cohesion Appendix A Definitions • Unconfined compressive strength – Load per unit area at which a soil will fail in compression Note: Estimated in the field by use of a pocket penetrometer, thumb penetration test, and other methods Appendix A Thread Test • Roll into thread • At least 2 inches in length • Longer unbroken thread means more cohesive Appendix A Ribbon Test • Roll soil into a cigar shape • Pinch between thumb and finger • Longer ribbon means more cohesive Appendix A Thumb Penetration Test Appendix A Pocket Penetrometer Appendix A Type A Soil • Most stable: clay, silty clay, and hardpan • Not fissured • Not subjected to vibration of any type • Never been previously disturbed • No seeping water Unconfined compressive strength greater than 1.5 tons per square foot (tsf) Appendix A Type B Soil • 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 but are fissured or subject to vibration Unconfined compressive strength less than 1.5 tsf and greater than 0.5 tsf Appendix A Type C Soil • Least stable: gravel, loamy sand, soft clay • Submerged soil or dense, heavy unstable rock • Soil from which water is freely seeping Unconfined compressive strength 0.5 tsf or less Appendix A Sloping and Benching • Contains definitions • Sets forth requirements • Configurations of sloping and benching Appendix B Allowable Slopes Soil Type Height/Depth Ratio Slope Angle Stable rock Vertical 90° Type A ¾:1 53° Type B 1:1 45° Type C 1½:1 34° Type A (short term) ½:1 63° (For a maximum excavation depth of 12 ft) Table B-1 Excavations Made in Type “A” Soil Simple Slope Excavations Made in Type “A” Soil Simple Slope – Short Term Excavations Made in Type “A” Soil Simple Bench Excavations Made in Type “A” Soil Unsupported Vertically-Sided Lower Portion Excavations Made in Type “A” Soil Unsupported Vertically-Sided Lower Portion Excavations Made in Type “A” Soil Multiple Bench Excavations Made in Type “A” Soil Support or Shield System Excavations Made in Type “B” Soil Simple Slope Excavations Made in Type “B” Soil Single Bench Excavations Made in Type “B” Soil Multiple Bench Excavations Made in Type “B” Soil Support or Shield System Excavations Made in Type “C” Soil Simple Slope Excavations Made in Type “C” Soil Support or Shield System Excavations Made in Layered Soils A over B Excavations Made in Layered Soils A over C Excavations Made in Layered Soils B over A Excavations Made in Layered Soils B over C Excavations Made in Layered Soils C over A Excavations Made in Layered Soils C over B Benching Benching and Sloping Timber Shoring for Trenches • Need to determine soil classification • Presentation of information • Basis and limitations of the data • Use of tables • Examples to illustrate the use of tables • Notes for all tables Appendix C Aluminum Hydraulic Shoring • Need to determine soil classification • Presentation of information • Basis and limitations of the data • Use of tables • Example to illustrate the use of the tables • Footnotes, and general notes Appendix D Figure No. 1 Vertical Aluminum Hydraulic Shoring (Spot Bracing) 18” Max.. Vertical Rail Vertical Spacing 4’ Max. Hydraulic Cylinder 2’ Max. Figure No. 2 Vertical Aluminum Hydraulic Shoring (With Plywood) Horizontal Spacing Vertical Rail Hydraulic Cylinder 18” Max. Vertical Spacing Plywood 4’ Max. 2’ Max. Figure No. 3 Vertical Aluminum Hydraulic Shoring (Stacked) Horizontal Spacing Hydraulic Cylinder Vertical Spacing 4’ Max. Vertical Rail 2’ Max. Figure No. 4 Aluminum Hydraulic Shoring Waler System (Typical) Horizontal Spacing Upright Sheeting Waler 2’ Max. Vertical Spacing 4’ Max. Hydraulic Cylinder Alternatives to Timber Shoring Appendix E Alternatives to Timber Shoring Appendix E Selection of Protective Systems • Illustrates a graphic summary of requirements contained in subpart P for excavations 20 feet or less in depth. • Protective systems for use in excavations more than 20 feet in depth must be designed by a registered professional engineer in accordance with 1926.652(b) and (c). Appendix F Your Questions?