Trenching

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# SPECIFIC EXCAVATION REQUIREMENTS (cont.) Oregon Administrative Rules Oregon Occupational Safety and Health Division # REQUIREMENTS FOR PROTECTIVE SYSTEMS P ## $1926.652 Requirements for Protective Systems. (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. (2) 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. - NOTE: The tables contained in Appendices A, B, C, D, E, and F do not contain sloping or shoring information for excavations over 20 feet deep. The protective systems for excavations over 20 feet in depth must be designed by a registered professional engineer in accordance with 1926.652(b) and (c). (b) Design of sloping and benching systems. The slopes and configurations of sloping and benching systems shall be selected and constructed by the employer or his designee and shall be in accordance with the requirements of paragraph (b)(1); or, in the alternative, paragraph (b)(2); or, in the alternative, paragraph (b)(3), or, in the alternative, paragraph (b)(4), as follows: (1) Option (1) - Allowable configurations and slopes. (i) Excavations shall be sloped at an angle not steeper than one and one-half horizontal to one vertical (34 degrees measured from the horizontal), unless the employer uses one of the other options listed below. (ii) Slopes specified in paragraph (b)(1)(i) of this section, shall be excavated to form configurations that are in accordance with the slopes shown for Type C soil in Appendix B to this subpart. (2) Option (2)…

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# Trenching and Excavation (cont.) ## Temporary protective structure (cont.) - Trench Boxes are commonly used in open areas that are away from utilities, roadways, and foundations. Trench boxes can be used to protect workers in cases of cave-ins, but not to shore up or support trench walls. They can support trench walls if the space between the box and the trench wall is backfilled with soil and compacted properly. Otherwise, a cave-in or collapse may cause the trench box to tilt or turn over. Workers should not be present in the box when it has to be moved. - Other: In some cases, the trench or excavation walls are made of rock but are not entirely stable. Support the walls by using rock bolts, wire mesh, or a method that provides equivalent support. ## What should NOT be done during an excavation? - Do not enter an unprotected trench deeper than 1.2 metres (4 feet), or as specified in the legislation. - Do not start digging before locating and de-energizing the buried services. - Do not enter a trench before testing the air for hazardous gasses and vapours, or the lack of oxygen. - Do not place the sections of pipes, piles of spoil, unused tools, and timber, and other materials within 1 metre from the trench's edge. - Do not rely on natural freezing to act as a method of soil stabilization. - Do not work under suspended or raised loads and materials. - Do not stand behind a backing vehicle. ## What can be included in a trenching and excavation inspection checklist? The following are some points to consider. Each circumstance will be different, so be sure to adapt the questions to suit your situation. ## Underground or Utility Services - Know the contact numbers? - Located, identified and informed respective parties? - Grounded, isolated, de-energized, or protected from unplanned release? ## Housekeeping Trenching and Excavation CCOHS

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# Trenching and Excavation (cont.) ## Housekeeping (cont.) - Excavated material, pipes etc. are placed 1 metre away from the edge of the excavation or trench wall? - Are pumps available to remove water? - Is the base and foot of the ladder secure, and free of garbage or water? - Are materials placed on the site obstructing the worker's or vehicle's ability to move freely? - Are established traffic controls used, where required, including adequate signage, personnel, and lighting? - Has the excavation been marked to make the workers and others aware of the excavation (e.g., fence, flags, or other safeguards)? - Are sanitary facilities available at the site, as appropriate? ## General - Are proper barriers or guardrails in place to protect anyone or equipment falling into the excavation or trench? - Has the air in the excavation been tested for low oxygen, and hazardous gasses and vapours? - Is a safe means of entry and exit provided such as a sufficiently long and secured ladder placed at appropriate distances (within 25 feet of all workers)? - Are cracks visible in the ground around the trench or excavation that may indicate soil movement? - Are there any signs of water seeping into the trench or excavation? - Are workers wearing appropriate PPE (e.g., hard hats, respirators, , safety boots, hearing protection)? - Are high visibility vests or clothing provided and worn by all exposed to vehicular traffic? - Is first aid equipment available at the site? - Are operators qualified to operate the heavy machinery or equipment? - Does a competent person regularly inspect the excavation (at the start of each shift before work begins or after any event likely to have affected the strength or stability of the excavation)? - Is there a competent person stationed at the surface of the trench to warn workers in the trench of danger and to provide emergency help? - Is the trench a confined space, and are the requirements of the confined space program met?…

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# Trenching and Excavation (cont.) ## What factors determine what is the appropriate protective system to use? (cont.) - Water content of soil - Changes due to weather or climate - Surcharge loads (e.g., spoil, other materials to be used in the trench) and - Other operations in the area Always check the legislative requirements in your jurisdiction related to the use of protective systems. ## What are the different types of protective systems used to protect against cave-ins? There are two basic methods of protecting workers against cave-ins: - Sloping - Temporary protective structures (e.g., shoring, trench boxes, pre-fabricated systems, hydraulic systems, engineering systems, etc.) ## Sloping Sloping involves cutting back the trench wall at an angle that is inclined away from the work area of the excavation. The angle of slope required depends on the soil conditions. Benching is a similar method to sloping. ## Temporary protective structure WorkSafe Saskatchewan defines a temporary protective structure as "a structure or device in an excavation, trench, tunnel or excavated shaft that is designed to provide protection from cave-ins, collapse, sliding or rolling materials, and includes shoring, trench boxes, trench shields and similar structures." Shoring is a system that supports the sides or walls. Shoring requires installing aluminum, steel, or wood panels that are supported by screws or hydraulic jacks. Some systems can be installed without the workers entering the trench. This option provides additional safety for those workers. Wherever possible, install the shoring equipment as the excavation proceeds. If there is any delay between digging and shoring, no one should enter the unprotected trench. Trenching and Excavation CCOHS

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# Trenching and Excavation (cont.) ## What are the hazards associated with trenching and excavation? (cont.) - Contact with buried service lines such as electrical, natural gas, water, sewage, telecommunications, etc. - Contact with overhead electrical lines. - Slips, trips and falls as workers climb on and off equipment, or from inappropriate access and egress methods. - Being struck by moving machinery, or by falling or flying objects. - Hazards related to materials handling (e.g., lifting, struck by, crushed between, etc.). ## What is meant by soil types? Definitions of soil types vary by jurisdiction in Canada. In addition, some jurisdictions have not defined soil types, but do require preventative measures when an excavation reaches a certain depth or proportion. When a soil type is defined, the purpose is to try to identify or predict the potential for the soil to move and cause a collapse while the work is being done. Soil types typically use a scale of 1 to 4 where 1 is hard and dense to 4 which is loose, soft, wet or muddy soil, or a scale of A to C where A is hard and solid, and C is soft, sandy, filled or loose. The soil type is determined by the characteristics of the soil's consistency, ease of removal, appearance, ability to excavate with hand tools vs. machine, water seepage, whether the soil has been excavated before, etc. ## What should occur before beginning an excavation? The employer or supervisor is responsible for the work, and must take the necessary steps to identify all the hazards and risks before beginning any work. These steps include to: - Identify the soil type(s) related to the excavation or trench you are going to dig. Soil properties often vary widely within a single trench (e.g., the soil type changes from top to bottom and along the length of a trench). - Look for the legislative requirements that apply in your jurisdiction and the type of protective measures to be taken. - Locate all buried services. Contact t…

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# Occupational Safety and Health Administration (cont.) ## Appendix B to Subpart P of Part 1926-Sloping and Benching (cont.) Short term exposure means a period of time less than or equal to 24 hours that an excavation is open. (c) Requirements (1) Soil classification. Soil and rock deposits shall be classified in accordance with appendix A to subpart P of part 1926. (2) Maximum allowable slope. The maximum allowable slope for a soil or rock deposit shall be determined from Table B-1 of this appendix. (3) Actual slope. (i) The actual slope shall not be steeper than the maximum allowable slope. (ii) The actual slope shall be less steep than the maximum allowable slope, when there are signs of distress. If that situation occurs, the slope shall be cut back to an actual slope which is at least ½ horizontal to one vertical (1/2H:1V) less steep than the maximum allowable slope. (iii) When surcharge loads from stored material or equipment, operating equipment, or traffic are present, a competent person shall determine the degree to which the actual slope must be reduced below the maximum allowable slope, and shall assure that such reduction is achieved. Surcharge loads from adjacent structures shall be evaluated in accordance with $ 1926.651(i). (4) Configurations. Configurations of sloping and benching systems shall be in accordance with Figure B-1. TABLE B-1 MAXIMUM ALLOWABLE SLOPES <table><tr><th>SOIL OR ROCK TYPE</th><th>MAXIMUM ALLOWABLE SLOPES (H:V)[1] FOR EXCAVATIONS LESS THAN 20 FEET DEEP[3]</th></tr><tr><td>STABLE ROCK</td><td>VERTICAL (90°)</td></tr><tr><td>TYPE A [2]</td><td>3/4:1 (53°)</td></tr><tr><td>TYPE B</td><td>1:1 (45°)</td></tr><tr><td>TYPE C</td><td>1/2:1 (34°)</td></tr></table> ## NOTES: 1. Numbers shown in parentheses next to maximum allowable slopes are angles expressed in degrees from the horizontal. Angles have been rounded off. Submit Feedback