Excavation Hazards & Procedures PDF

Objective 7 Explain the hazards of excavation, and describe typical excavation procedures and permits EXCAVATION DEFINITIONS CAUTION The information on excavation below is based on information available from the British Columbia OH&S Regulation. This information is presented as an example only and...

Objective 7 Explain the hazards of excavation, and describe typical excavation procedures and permits EXCAVATION DEFINITIONS CAUTION The information on excavation below is based on information available from the British Columbia OH&S Regulation. This information is presented as an example only and should not be construed as exact or applicable to all jurisdictions. Nor should the wording be accepted as the exact wording in the BC OH&S Regulation. An excavation is any cut, cavity, trench, or depression in the earth’s surface resulting from rock or soil removal. A trench is an excavation that is less than 3.7 m wide at the bottom, over 1.2 m deep, and of any length. Another term often associated with excavation and trenching is ground disturbance. Ground disturbance is any work, operation, or activity that results in a disturbanceor displacement of the earth to a depth greater than 30 cm. The following are the hazards associated with ground disturbance, excavation, and trenching: • Caving in, sloughing, or collapsing of walls or sides • Contact with buried services • Contact with foundations, adjacent structures, or buildings • Creation of confined or restricted spaces during or after excavation • Excavated material • Falling objects or objects near the excavation • Flooding and water accumulation • Powered mobile equipment • Slips, trips, and falls • Formation of a toxic or explosive atmosphere All these hazards must be removed, secured, or mitigated so as not to endanger workers. To protect workers from the caving in, sloughing, or collapsing of walls or sides in an excavation or trench, methods such as shoring, or sloping are used. Shoring is a system of aluminum, steel, or wood panels that are installed in the excavation or trench to support the walls or sides. Sloping involves cutting back the excavation or trench wall at an angle that is inclined away from the work area. Figure 7 shows an example of a trench with shoring. Figure 8 shows an example of an excavation with sloped sides. Page 30 of 56 EXCAVATION PROCEDURES and PERMITS Ground disturbance, excavation, and trenching are common on some job sites. Workers in the excavation or trench must be protected. The two most common types of trenching used to protect the workers are straight cut trenching with shoring and open cut trenching with proper sloping on the sides. Weather and the passing of time can vary trench conditions significantly, so ongoing observation of soil conditions is part of the work process. A ground disturbance or excavation procedure should consider at least the following information: a) When heavy equipment and structures are located near the trench, a professional engineer should be consulted b) Prior to the commencement of any trenching, all involved utility companies shall be notified and utilities located. If overhead power lines are close to the excavation, they must be protected or removed. c) All underground lines shall be hand-exposed under the direction of the supervisor. d) Access to the excavation should be from the upwind side. e) A monitor capable of detecting hydrogen sulfide (H2S) and the lower explosive limit (LET) of a hydrocarbon gas or vapour shall be used to ensure the trench is free of toxic or explosive gases f) Entry and exit steps should be cut into the wall of the trench, or a ladder should be provided so that at least one metre protrudes above the top of the trench on the upwind bank. Page 31 of 56 g) Where a trench or bulk excavation with sloping sides or walls is used, the OH&S Regulation and company procedures should be referenced for the specific situation h) All shoring and support structures must comply with the OH&S Regulation and company procedures. i) Temporary protective structures shall be designed by a professional engineer. All workers required to work in or around an open excavation or trench must follow a written ground disturbance or excavation permit that has been specifically designed for the work site. Someone who is fully trained and experienced in ground disturbance, excavation, or trenching work should complete the ground disturbance or excavation permit. This permit is required in addition to a standard safe work permit. A ground disturbance permit required for excavation or trenching is a planning tool designed to ensure that the work involving a disturbance of the ground does not result in any of the following: a) Injury or loss of life to workers b) Harm to the environment c) Damage to buried services or adjacent structures Page 32 of 56