Safety in Excavations

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Safety factors for excavations at construction sites

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  • 1926 Subpart P ‑ Excavations
    This presentation is designed to assist trainers conducting OSHA 10-hour Construction Industry outreach training for workers. Since workers are the target audience, this presentation emphasizes hazard identification, avoidance, and control – not standards. No attempt has been made to treat the topic exhaustively. It is essential that trainers tailor their presentations to the needs and understanding of their audience.
    This presentation is not a substitute for any of the provisions of the Occupational Safety and Health Act of 1970 or for any standards issued by the U.S. Department of Labor. Mention of trade names, commercial products, or organizations does not imply endorsement by the U.S. Department of Labor.
  • Reference 1926.650
    Shield (shield system) -- a structure able to withstand a cave-in and protect employees with the structure. Shields can be permanent structure or can be designed to be portable and moved along as work progresses. Also known as trench box or trench shield.
    Shoring (shoring system) -- a structure such as a metal hydraulic, mechanical or timber shoring system that supports the sides of an excavation and which is designed to prevent cave-ins.
    Sloping (sloping system) -- protects employees from cave-ins by excavating to form sides of an excavation that are inclined away from the excavation to prevent cave-ins. The angle of incline varies with differences in such factors as the soil type, environmental conditions of exposure, and application of surcharge loads.
  • Reference 1926.652(a)
    Protective system – a method of protecting employees from cave-ins, from material that could fall or roll from an excavation face or into an excavation, or from the collapse of adjacent structures. Protective systems include support systems, sloping and benching systems, shield systems, and other systems that provide the necessary protection.
  • Reference 1926.652(a)
    Each employee in an excavation shall be protected from cave-ins by an adequate protective system except when:
    Excavations are made entirely in stable rock; or
    Excavations are less than 5 feet in depth and examination of the ground by a competent person provides no indication of a potential cave-in.
    Protective systems shall have the capacity to resist without failure all loads that are intended or could reasonably be expected to be applied or transmitted to the system.
    Reference 1926.652(b) Design of sloping and benching systems.
  • Several factors come into play when developing a total “protective system”. The design of of the system itself, how materials and equipment are handled in and around the excavation, and installation and removal of protective system components.
  • Reference 1926.652, 1926.652(b), 1926.652(c)
    Benching -- excavating the sides of an excavation to form one or a series of horizontal levels or steps, usually with vertical or near-vertical surfaces between levels.
    Shoring or shielding is used when the location or depth of the cut makes sloping back to the maximum allowable slope impractical. There are two basic types of shoring, timber and aluminum hydraulic.
    Trench boxes (shielding) are different from shoring because instead of supporting the trench face, they are mostly serve to protect workers from cave-ins. The excavated area between the outside of the trench box and the face of the trench should be as small as possible. The space between the trench box and the excavation side may be backfilled (or other means may be used) to prevent lateral movement of the box. Shields may not be subjected to loads exceeding those which the system was designed to withstand. Trench boxes may be used in combination with sloping and benching.
  • Reference 1926.652(a) and 1926.652(c)(1)
    Designs for aluminum hydraulic shoring shall be in accordance with paragraph (c)(2), but if manufacturer's tabulated data cannot be utilized, designs shall be in accordance with appendix D.
    Employees exposed to potential cave-ins must be protected by sloping or benching the sides of the excavation, by supporting the sides of the excavation, or by placing a shield between the side of the excavation and the work area.
    1926 Subpart P Appendix D Aluminum Hydraulic Shoring for Trenches
    Contains information that can be used when aluminum hydraulic shoring is provided as a method of protection against cave-ins in trenches that are not more than 20 feet deep.
  • Reference 1926.652(a) and (b) and (c)
  • 1926.652(c)
    The employer or his designee must select and construct designs of support systems, shield systems, and other protective systems
    Trenches more than 5 feet require shoring or must have a stabilized slope
    Trenches less than 5 feet - a competent person must inspect to determine that a protection system is not necessary in soils where there is no indication of a potential cave-in
    In hazardous soil conditions trenches under 5 feet need protection
  • Reference 1926.652 (d)
    Materials and equipment used for protective systems shall be free from damage or defects that might impair their proper function.
    Manufactured materials and equipment used for protective systems shall be used and maintained in a manner that is consistent with the recommendations of the manufacturer, and in a manner that will prevent employee exposure to hazards.
    When material or equipment that is used for protective systems is damaged, a competent person shall examine the material or equipment and evaluate its suitability for continued use. If the competent person cannot assure the material or equipment is able to support the intended loads or is otherwise suitable for safe use, then such material or equipment shall be removed from service, and shall be evaluated and approved by a registered professional engineer before being returned to service.
  • Reference 1926.651(f) Warning system for mobile equipment
    When mobile equipment is operated adjacent to an excavation, or when such equipment is required to approach the edge of an excavation, and the operator does not have a clear and direct view of the edge of the excavation, a warning system shall be utilized such as barricades, hand or mechanical signals, or stop logs. If possible, the grade should be away from the excavation.
  • In addition to the unprotected trench, a cave-in hazard is increased by machinery which gets too close.
    Even normal vehicular traffic, such as that along an adjacent interstate or road through an industrial part may impact an excavation. The vibrations from continuous or heavy traffic may undermine the soil and cause a cave-in.
  • Reference 1926.651(j)(2)
    Protect employees from materials or equipment that could fall or roll into excavations.
    You may also use retaining devices that are sufficient to prevent materials or equipment from falling or rolling into excavations
  • Safety in Excavations

    1. 1. Excavations & Trenching PPT-011-01 1
    2. 2. Definitions • "Excavation" means any: • 1. Man-made cut • 2. Cavity • 3. Trench • 4. Depression in an earth surface, formed by earth removal. 2
    3. 3. Definitions • Confined space is a space that, by design and/or configuration has: • 1. Limited openings for entry and exit • 2. Unfavorable natural ventilation • 3. May contain or produce hazardous substances • 4. Is not intended for continuous employee occupancy. 3
    4. 4. Objectives • Highlight the hazards of working in a excavation. • How to protect employees from cave-ins. • Factors that pose a hazard to employees working in excavations. • The role of a competent person at an excavation site.
    5. 5. General Requirements • Before any excavation actually begins, determine the estimated location of Sewer, telephone, fuel, electric, water under ground installations that may be digging. the employer must utility installations: lines, or any other encountered during • A competent person will inspect, on a daily basis, excavations and adjacent areas for possible cave-ins, failure of protective systems and equipment, hazardous atmospheres, or other hazardous conditions. • Takes prompt corrective measures to eliminate hazards. • Adequate protective systems will be utilized to protect employees. This can be accomplished through: Sloping, Shoring, or Shielding.
    6. 6. General Requirements • Workers must be supplied with and wear any PPE deemed necessary to assure their protection. • Mechanical excavators and power tools should not be used within 0.5 m • If a trench is 4 feet or deeper, stairways, ramps, or ladders will be used. • The employees must not have to travel any more than 25 feet to reach the stairways, ramps, or ladders. • 4 feet and more trenches – Toxic and hazardous atmosphere will be tested daily.
    7. 7. Definitions • Excavation – a man-made cut, cavity, trench or depression formed by earth removal. • Trench – a narrow excavation. The depth is greater than the width, but not wider than 15 feet. • Shield - A structure able to withstand a cave-in and protect employees (also called box). • Shoring - A structure that supports the sides of an excavation and protects against cave-ins. • Sloping - A technique that employs a specific angle of incline on the sides of the excavation. The angle varies based on assessment of impacting site factors.
    8. 8. Definitions 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.
    9. 9. Excavation Hazards – Surface encumbrances – Utilities – Access/Egress – Vehicle traffic – Falling loads – Mobile equipment – Hazardous atmospheres – Water accumulation – Adjacent structures – Loose rock or soil – Falls – Cave-in
    10. 10. Definitions Cave-In: • Means the separation of a mass of soil or rock material from the side of an excavation, or the loss of soil from under a trench shield or support system, and its sudden movement into the excavation, either by falling or sliding, in sufficient quantity so that it could entrap, bury, or otherwise injure or immobilize a person.
    11. 11. Anatomy of a Cave - In: There is usually no warning before a cave-in
    12. 12. Causes of Cave – Ins
    13. 13. Causes of Cave – Ins  When water is present in an excavation it is extremely hazardous to enter. Also no head protection
    14. 14. Causes of Cave – Ins  Note: telephone pole adjacent to excavation, not supported / removed
    15. 15. Injury and Death • Excavating is one of the most hazardous construction operations • Most accidents occur in trenches 515 feet deep • There is usually no warning before a cave-in 16
    16. 16. Protection of Employees • Employees should be protected from cave-ins by using an adequately designed protective system. • Protective systems must be able to resist all expected loads to the system. 17
    17. 17. Protect Employees Exposed to Potential Cave-ins • Slope or bench the sides of the excavation. • Support the sides of the excavation. • Place a shield between the side of the excavation and the work area. 18
    18. 18. Requirements for Protective Systems A well-designed protective system Correct design of: - Sloping and benching systems - Support systems - Shield systems - Other protective systems + Appropriate handling of materials and equipment + Attention to correct installation and removal = Protection of employees at excavations. 19
    19. 19. Design of Protective Systems The employer shall select and construct : →Slopes and configurations of sloping and benching systems. →Support systems, shield systems and other protective systems. • Shield - Can be permanent or portable. Also known as trench box or trench shield. • Shoring - Such as metal hydraulic, mechanical or timber shoring system that supports the sides. • Sloping - Formed sides of an excavation that are inclined away from the excavation. 20
    20. 20. 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 21
    21. 21. 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. 22
    22. 22. Cave-in Hazard Inadequate protective system This excavation has inadequate support posts and egress access. PPT-011-01 23
    23. 23. Inadequate Protective System This worker is in a trench, with no protective system, that is neither sloped nor benched, and has no means of egress. • PPT-011-01 24
    24. 24. Factors Involved in Designing System a Protective • Soil classification • Depth of cut • Water content of soil • Changes due to weather and climate • Other operations in the vicinity PPT-011-01 25
    25. 25. Shoring • General • Provides a framework in which to work • Uses walls, cross braces and uprights • Supports excavation walls • Must know soil type • Must know depth and width of excavation 26
    26. 26. Trench Shield A trench shield (also called a trench box) was built around this work area. PPT-011-01 27
    27. 27. Hydraulic Trench Support • Using hydraulic jacks, the operator can easily drop the system into the hole. • Once in place, hydraulic pressure is increased to keep the forms in place. • Trench pins are installed in case of hydraulic failure. PPT-011-01 28
    28. 28. Materials and Equipment • Equipment used for protective systems must not have damage or defects that impair function. • If equipment is damaged, a competent person must examine it to see if it is suitable for continued use. • If not suitable, remove it from service until a professional engineer approves it for use. PPT-011-01 Trench Box 29
    29. 29. Protection from Vehicles • Install barricades • Hand/mechanical signals • Stop logs • Grade soil away from excavation • Fence or barricade trenches left overnight 30
    30. 30. Hazardous Conditions They should not be working under this crane. The weight and vibration of the crane makes this a very hazardous condition. PPT-011-01 31
    31. 31. Spoil Piles • Don’t place spoils within two feet from edge of excavation. • Measure from nearest part of the spoil to the excavation edge. • Place spoils so rainwater runs away from the excavation. • Place spoil well away from the excavation. 32
    32. 32. Other Excavation Hazards • Water accumulation • Oxygen deficiency • Mobile equipment • Access/egress • Toxic fumes • Falls PPT-011-01 33
    33. 33. Access The ladder should extend 3 feet above the excavation
    34. 34. Access These two ladders which are lashed together are not an adequate means of egress The ladder should extend 3 rungs above the top of the excavation
    35. 35. Ladder to be 1 Meter Above Wall
    36. 36. Excavation Protection Systems • There are three basic protective systems used in excavations and trenches: 1. Sloping and Benching Systems 1. Shoring Systems 2. Shielding Systems
    37. 37. Simple Sloping
    38. 38. Benching
    39. 39. Shoring Systems  Support system for trench faces used to prevent movement of soil, underground utilities, foundations.  There are two basic types of shoring, timber and aluminum hydraulic.
    40. 40. Shoring Systems
    41. 41. Timber Shoring Installations
    42. 42. Hydraulic Shoring
    43. 43. Pneumatic Shoring
    44. 44. Shielding Systems A- Trench Boxes:  The space between the outside of the trench box and the face of the trench should be small as possible, and backfilled to prevent lateral movement of the box.
    45. 45. Excavation Inspections • Daily Inspections of ALL excavations by Competent Person at Start of shift, or as needed, following rainstorms or other hazard-increasing event: • Possible cave-ins • Protective system failure • Water accumulation • Hazardous atmospheres Competent person has authority to remove workers from the excavation
    46. 46. Inadequate Protective System  This excavation has inadequate support posts and egress access.
    47. 47. Inadequate Protective System  This worker is in a trench with no protective system, that is not sloped or benched and has no means of egress.
    48. 48. Hazardous Condition  The weight and vibrations of the machinery above make this a very hazardous condition.  They should not be working under any machinery.
    49. 49. Hydraulic Trench Support  Using hydraulic jacks the operator can easily drop the system into the hole.  Once in place, hydraulic pressure is increased to keep the forms in place.  Trench pins are installed in case of hydraulic failure.
    50. 50. Hazardous Atmosphere  Test excavations more than 4 feet before an employee enters the excavation for:  Oxygen deficiency.  High combustible gas concentration.  High levels of other hazardous substances.
    51. 51. Means of egress • Means of egress from trench excavations: • 1. 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. • 2. A means of egress should require no more than 25 feet (7.62 m) of lateral travel for any employee to reach. 52
    52. 52. 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: • 1. Possible cave-ins • 2. Indications of failure of protective systems • 3. Hazardous atmospheres • 4. Other hazardous conditions. 53
    53. 53. Inspections Cont. • An inspection shall be conducted by the competent person: • 1. Prior to the start of work and as needed throughout the shift. • 2. After every rainstorm or other hazard increasing occurrence. • 3. These inspections are only required when employee exposure can be reasonably anticipated. 54
    54. 54. Safety considerations • Excavation is one of the most hazardous types of work in the construction industry • Accidents result from inadequate planning • Build safety into pre-bid planning • Plan safety into the job. Consider: – Traffic – Nearness of structures and their conditions – Soil
    55. 55. Safety considerations • Plan safety into the job. Consider: – Surface and ground water – Water table – Overhead/ underground utilities – Weather
    56. 56. Jobsite safety and health programs • Establish and maintain a safety and health program for the worksite • Provide adequate systematic policies, procedures, practices • Recognize job-related safety/health hazards
    57. 57. Jobsite safety and health programs • Safety and health programs should reflect the unique characteristics of the jobsite • Proper implementation depends on cooperation among: – supervisors – employee groups – individual employees
    58. 58. Locating utilities • Employers must determine the estimated locations of utility installations • Contact utility companies before starting excavation • Utility owners must attempt to find exact location of utilities • Proceed with caution if the exact location of utilities cannot be found • Use safe and acceptable means to locate exact locations of installations
    59. 59. Safety starts at the surface • Surface encumbrances that create hazards must be removed/supported • Wear warning vests when near traffic • Employees must be trained to operate heavy equipment • Stay away from loads being handled by lifting/digging equipment
    60. 60. Safety starts at the surface • Warn mobile equipment operators about the edge of the excavation site • Keep the grade away from the excavation site • Stay away from vehicles being loaded/unloaded
    61. 61. Employee access/egress from excavations • Ramps must be designed by a competent person • Ramps must be structurally sound and not create a tripping hazard • Use surface treatments on ramps to prevent slipping • Trenches 4 or more feet deep need a safe means of egress – Stairway – Ladder – Ramps • Means of egress must be fixed and secure
    62. 62. Employee access/egress from excavations • Means of egress must be within 25 feet of workers • Ladders must extend a minimum of 36 inches above the landing • Use metal ladders with caution around utilities

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