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NGI-Excavation Hazards
- 1. Excavations
- 5. Collapse of spoil soil
- 7. Sloping
- 8. Shoring
- 9. Cave-in Hazard This excavation has inadequate support posts and egress access Inadequate protective system
- 10. 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
- 11. Underground services Digging into underground services can lead to: • fires and explosions from ruptured gas pipes; • contamination of fresh water supplies; • flooding from ruptured water and sewerage pipes; • soil contamination from burst fuel pipes; • loss of communication and electric power services; and • electrocution due to cutting of Electrical cable .
- 12. Preventing damage to cables and pipes Dig trial holes to confirm the position of cables and pipes . Dig along-side the line of the cable or pipe, not directly above. Have an observer to guide the operator. Use shovels and spades to make the final exposure. Avoid using: • picks or forks ; • jack hammers near plastic pipes and electric cables; and • explosives within 30 metres of a gas pipe.
- 13. Falling into Excavation Set up barriers or barricades around the edges of the excavation. Place warning signs to warn people of the excavation. Divert traffic away from the excavation area Install flashing amber lights for night-time warning.
- 15. Hazardous Conditions The weight and vibrations of the crane make this a very hazardous condition. They should not be working under this crane.
- 17. Water = Cave-in Hazard These workers must be protected from cave-in. Note the water in the bottom of the trench. This is a very hazardous condition!
- 20. Access and Egress These two ladders which are lashed together are not an adequate means of egress The ladder should extend 3 feet above the top of the excavation
Notas del editor
- 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.
- Instructor note: OSHA Standard Exemptions: House foundation/basement excavations (including those that become trenches by definition when formwork, foundations, or walls are constructed) are exempt from the OSHA standard. The specific information regarding the interpretation of this exemption may be found on the OSHA public web site. Reference 29 CFR 1926.652. The exemption specifies height and width for the excavation, impact of water and environmental conditions, soil and equipment factors, and operation of heavy equipment in the vicinity.
- 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, 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)
- 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.
- 1926.651(h) Employees shall not work in excavations in which there is accumulated water, or in excavations in which water is accumulating, unless adequate precautions have been taken to protect employees against the hazards posed by water accumulation. The precautions necessary to protect employees adequately vary with each situation, but could include special support or shield systems to protect from cave-ins, water removal to control the level of accumulating water, or use of a safety harness and lifeline. If water is controlled or prevented from accumulating by the use of water removal equipment, the water removal equipment and operations shall be monitored by a competent person to ensure proper operation. If excavation work interrupts the natural drainage of surface water (such as streams), diversion ditches, dikes, or other suitable means shall be used to prevent surface water from entering the excavation and to provide adequate drainage of the area adjacent to the excavation.
- Must also test where oxygen deficiency or a hazardous atmosphere could reasonably be expected to exist, before an employee enters the excavation. If hazardous conditions exist, controls such as proper respiratory protection or ventilation must be provided. Also, controls used to reduce atmospheric contaminants to acceptable levels must be tested regularly. Where adverse atmospheric conditions may exist or develop in an excavation, the employer also must provide and ensure that emergency rescue equipment, (e.g., breathing apparatus, a safety harness and line, basket stretcher, etc.) is readily available. This equipment must be attended when used. Employees shall not be permitted to work in hazardous and/or toxic atmospheres. Such atmospheres include those with: -- less than 19.5% oxygen, -- a combustible gas concentration greater than 20% of the lower flammable limit, and, -- concentrations of hazardous substance that exceed those specified in the Threshold Limit Values for airborne contaminants established by the ACGIH.
- Reference 1926.651(c(1) Structural ramps - Structural ramps that are used solely by employees as a means of access or egress from excavations shall be designed by a competent person. Structural ramps used for access or egress of equipment shall be designed by a competent person qualified in structural design, and shall be constructed in accordance with the design. - Ramps and runways constructed of two or more structural members shall have the structural members connected together to prevent displacement. - Structural members used for ramps and runways shall be of uniform thickness. - Cleats or other appropriate means used to connect runway structural members shall be attached to the bottom of the runway or shall be attached in a manner to prevent tripping. - Structural ramps used in lieu of steps shall be provided with cleats or other surface treatments o the top surface to prevent slipping.
- Reference 1926.651(c) and 1926.1053 (ladder)
- Reference 1926.651(k) 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.
- Reference 1926.651(k) (2) Where the competent person finds evidence of a situation that could result in a possible cave-in, indications of failure of protective systems, hazardous atmospheres, or other hazardous conditions, exposed employees shall be removed from the hazardous area until the necessary precautions have been taken to ensure their safety.
- The following concerns must be addressed by a competent person: Evaluate soil conditions [1926 Subpart P Appendix A] and select appropriate protective systems [1926 Subpart P Appendix F]. Construct protective systems in accordance with the standard requirements [1926.652]. Preplan; contact utilities (gas, electric) to locate underground lines, plan for traffic control if necessary, determine proximity to structures that could affect choice of protective system. Test for low oxygen , hazardous fumes and toxic gases, especially when gasoline engine-driven equipment is running, or the dirt has been contaminated by leaking lines or storage tanks. Insure adequate ventilation or respiratory protection if necessary. Provide safe access into and out of the excavation. Provide appropriate protections if water accumulation is a problem. Inspect the site daily at the start of each shift, following a rainstorm, or after any other hazard-increasing event. Keep excavations open the minimum amount of time needed to complete operations. Surface crossing of trenches should not be made unless absolutely necessary. However, if necessary, they are only permitted under the following conditions: -- Vehicle crossings must be designed by and installed under the supervision of a registered professional engineer. -- Walkways or bridges must: -- have a minimum clear width of 20 inches, -- be fitted with standard rails, and -- extend a minimum of 24 inches past the surface edge of the trench.
- Reference 1926.650(b) "Competent person" One who is capable of identifying existing and predictable hazards in the surroundings, or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them. Preamble Page 45909 – “Competent Person” The term is used throughout existing subpart P, but was not defined within the subpart, and there were no references to the existing definition in subpart C, in the proposal, OSHA added the definition to subpart P to help those using the standard.