1.0 PURPOSE
The purpose of this procedure is to provide written instructions for Nitro Construction Services in the general protection requirements of excavations, trenching, and shoring.
2.0 RESPONSIBILITY
It is the responsibility of the Site Manager/Superintendent to implement the requirements of this procedure or secure the services of a qualified Excavation Competent Person.
3.0 REFERENCES
29 CFR 1926.650
29 CFR 1926.651
29 CFR 1926.652
4.0 DEFINITIONS
4.1 Excavation – Any man-made cavity or depression in the earth’s surface, including its sides, walls, or faces, formed by earth removal and producing unsupported earth conditions by reasons of the excavation.
4.2 Angle of Repose – The greatest angle above the horizontal plane at which a material will remain stable without sliding.
4.3 Bank – A mass of soil rising above a digging level.
4.4 Belled Excavation – A part of a shaft or footing excavation, usually near the bottom and bell-shaped.
4.5 Benching – A method of protecting employees from cave-ins by 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.
4.6 Braces – The horizontal members of the shoring system whose ends bear against the uprights or stringers.
4.7 Cave-in – 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 and immobilize a person.
4.8 Competent Person for Excavation – One who is capable of identifying existing and predictable hazards in the surroundings, or working conditions which are unsanitary, hazardous, or dangerous to employees, has the authority to take prompt corrective measures to eliminate them and has the appropriate training.
4.9 Cross braces – the horizontal members of a shoring system installed perpendicular to the sides of the excavation, the ends of which bear against either uprights or wales.
4.10 Excavation – any man-made cut, cavity, trench, or depression in an earth surface, formed by earth removal.
4.11 Faces or Sides – The vertical or inclined earth surfaces formed as a result of excavation work.
4.12 Failure – The breakage, displacement, or permanent deformation of a structural member or connection so as to reduce its structural integrity and its supportive capabilities.
4.13 Hazardous Atmosphere – An atmosphere which by reason of being explosive, flammable, poisonous, corrosive, irritating, oxygen-deficient, toxic, or otherwise harmful, may cause death, illness, or injury.
4.14 Kickouts – Accidental release or failure of a shore or brace.
4.15 Layered Systems – Two or more distinctly different soil or rock types arranged in layers.
4.16 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.
4.17 Ramp – an inclined walking or working surface that is used to gain access to one point from another, and is constructed from earth or from structural materials such as steel or wood.
4.18 Registered Professional Engineer – a person who is registered as a professional engineer in the state where the work is to be performed.
4.19 Sheet pile – A pile, or sheeting, that may form one of a continuous interlocking line, or a row of timber, concrete, or steel piles, driven in close contact to provide a tight wall to resist the lateral pressure of water, adjacent earth, or other material.
4.20 Shield (Shield system) – a structure that is able to withstand the forces imposed on it by a cave-in and thereby protect employees within the structure. Shields can be permanent structures or can be designed to be portable and moved along as work progresses. Shields used in trenches are usually referred to as “trench boxes” or “trench shields.”
4.21 Shoring (Shoring system) – a structure such as a metal hydraulic, mechanical, or timber shoring system that supports the sides of an excavation which is designed to prevent cave-ins.
4.22 Slope – The angle with the horizontal at which a particular earth material will stand indefinitely without movement.
4.23 Stringers – The horizontal members of a shoring system whose sides bear against the uprights or earth.
4.24 Structural ramp – a ramp built of steel or wood, usually used for vehicle access. Ramps made of soil or rock are not considered structural ramps.
4.25 Support system – a structure such as underpinning, bracing, or shoring, which provides support to an adjacent structure, underground installation, or the sides of an excavation.
4.26 Trench – A narrow excavation made below the surface of the ground. In general, the depth is greater than the width, but the width of a trench is no greater than 15 feet. If forms or other structures are installed or constructed in an excavation so as to reduce the dimension measured from the forms or structure to the side of the excavation to 15 feet or less (measured at the bottom of the excavation), the excavation is also considered to be a trench.
4.27 Trench Box – See Shield (Shield System)
4.29 Trench Shield – See Shield (Shield System)
4.30 Uprights – The vertical members of a trench shoring system placed in contact with the earth and usually positioned so that individual members do not contact each other. Uprights placed so that individual members are closely spaced, in contact with or interconnected to each other, are often called “sheeting.”
5.0 PROCEDURE
5.1 An initial evaluation of the proposed excavation shall be conducted by the competent person using the criteria set forth below and document on the Trenching and Excavation Initial Evaluation Form (NCS Form 024) or equivalent OSHA 1926 Excavation Checklist.
5.2 Before opening any excavation, efforts shall be made, including utility contact, to determine if there are underground utility installations (i.e., electricity, fuel, water, sewer, etc.) in the area, and they shall be located, supported, and protected during the excavation operations.
5.3 The walls and faces of trenches 5 feet deeper, and all excavations in which employees may be exposed to danger from moving ground or cave-in shall be guarded by a shoring system, sloping of the ground, or some other equivalent means.
5.4 All employees working in or around excavations or trenches shall be required to wear personal protective equipment for the head, eyes, respiratory organs, hands, feet, and other parts of the body as deemed necessary by the hazards present.
5.5 Employees exposed to heavy equipment vehicular traffic shall be required to wear a reflector type warning vest.
5.6 In excavations which employees may be required to enter, excavated or other material shall be effectively stored and retained at least 2 feet or more from the edge of the excavation.
5.7 Ladders or steps shall be used to enter and exit trenches 4 feet or more in-depth. Ladders or steps shall be located at a distance not greater than 25 feet laterally. When ladders are being used they shall extend a minimum of 3 feet above the top of the trench.
5.8 As a minimum, all excavations, trenches, ditches, etc. shall be barricaded and have warning signs posted. Guardrails will be installed for crossings and walkways to protect against falls.
5.9 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.
5.9.1 Ramps and runways constructed of two or more structural members shall have the structural members connected together to prevent displacement.
5.9.2 Structural members used for ramps and runways shall be of uniform thickness.
5.9.3 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.
5.9.4 Structural ramps used in lieu of steps shall be provided with cleats or other surface treatments on the top surface to prevent slipping.
5.9.5 Walkways shall be provided where employees or equipment are required or permitted to cross over excavations. Guardrails that comply with 1926.502(b) shall be provided where walkways are 6 feet (1.8 m) or more above lower levels.
5.10 A stairway, ladder, ramp or other safe means of egress shall be located in trench excavations that are 4 feet or more in-depth so as to require no more than 25 feet of lateral travel for employees.
5.11 Daily inspections of excavations, the adjacent areas, and protective systems shall be made by the excavation competent person and documented on the Trenching and Excavation Daily Inspection form. If evidence of possible cave-ins, slides, failure of protective systems, hazardous atmospheres, or other hazardous conditions is apparent, all work in the excavation shall cease until the necessary precautions have been taken to safeguard the employees.
5.11.1 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.
5.11.2 These inspections are only required when employee exposure can be reasonably anticipated.
5.12 When possible, dust conditions should be kept to a minimum by the use of water, salt, calcium chloride, or other acceptable means.
5.13 In locations where undesirable atmospheric conditions may exist, the excavation or trench shall be tested before employees enter excavations greater than 4 feet in depth. If necessary, controls as set forth in sub-parts D and E of 29 CFR 1926 (occupational health, environmental controls, PPE, and lifesaving equipment) shall be established to assure employee safety. When controls are used that are intended to reduce the level of atmospheric contaminants to acceptable levels, testing shall be conducted as often as necessary to ensure that the atmosphere remains safe.
5.14 Where adverse conditions may exist or develop in an excavation, emergency rescue equipment such as breathing apparatus, a safety harness, and line, basket stretcher, etc. shall be readily available. This equipment shall be attended when in use.
5.15 Employees shall not be allowed to work in excavations in which water has accumulated or is accumulating unless adequate precautions have been taken to protect employees against the hazards posed by the water accumulation. Specific precautions may vary with each situation but may include special support or shield systems to protect against cave-ins, water removal to control the accumulating water, or the use of a safety harness and lifeline. If the water is controlled by water removal equipment, this equipment and operation shall be monitored by a competent person to ensure proper operation.
5.16 Excavations below the level of the base or footing of any foundation or retaining wall shall not be permitted except when:
5.16.1 A support system, such as underpinning, is provided to ensure the safety of employees and the stability of the structure; or
5.16.2 The excavation is in stable rock; or
5.16.3 A registered professional engineer has approved the determination that the structure is sufficiently removed from the excavation so as to be unaffected; or
5.16.4 A registered professional engineer has approved the determination that such excavation work will not pose a hazard to employees.
5.16 Work in or around excavations or trenches should never be performed alone.
5.17 Employees will be protected against potentially falling loads and are not permitted to work under loads of digging equipment where loads may fall.
5.18 In addition to the guidelines of this procedure, all safety precautions and guidelines of the customer facility shall be followed.
6.0 SOIL CLASSIFICATION
6.1 Each soil and rock deposit at an excavation site must be classified by the excavation competent person as stable rock, Type A, Type B, or Type C soil.
6.1.1 Stable rock refers to a natural solid mineral matter which can be excavated with vertical sides and remain intact while exposed.
6.1.2 Type-A soil is cohesive with an unconfined compressive strength of 1.5 tons per square foot (tsf). Type A soils include clay, silty clay, sandy clay, clay loam, caliche, hardpan, and sometimes silty clay loam and sandy clay loam.
6.1.2.1 No soil should be classified as Type A if it is fissured; subject to vibration from traffic, pile driving, or similar effects; previously disturbed; or part of a sloped, layered system where the slope is four horizontal to one vertical or greater.
6.1.3 Type B soil is cohesive soil with an unconfined compressive strength greater than 0.5 tons per square foot but less than 1.5 tons per square foot. Type B soils include granular cohesionless soils like angular gravel, silt, silt loam, sandy loam, and sometimes silty clay loam and sandy clay loam; previously disturbed soils that are not Type C; fissured soils and soils subject to a vibration that would otherwise be classified as Type A; dry rock that is not stable; and material that is part of a sloped, layered system where the layers dip on a slope less steep than four horizontal to one vertical.
6.1.4 Type C soil is cohesive soil with an unconfined compressive strength of 0.5 ton per square foot or less. Type C soils include granular soils such as gravel, sand, and loamy sand; submerged soil; soil from which water is freely seeping; submerged rock that is not stable; or material in a sloped, layered system where the layers dip into the excavation at a slope of four horizontal to one vertical or steeper.
6.1.5 Soil classification is to be based on at least one visual analysis and one manual analysis of the soil.
6.1.6 Visual Test:
6.1.6.1 Observe samples of soil that are excavated and soil on the sides of the excavation. Estimate the range of particle sizes and the relative amounts of the particle sizes. Soil that is primarily composed of fine-grained material is cohesive material. Soil composed primarily of coarse-grained sand or gravel is a granular material.
6.1.6.2 Observe the soil as it is excavated. Soil that remains in clumps when excavated is cohesive. Soil that breaks up easily and does not stay in clumps is granular.
6.1.6.3 Observe the sides of the opened excavation and the surface area adjacent to the excavation. Crack-like openings such as tension cracks could indicate fissured material. If chunks of soil spall off a vertical side, the soil could be fissured. Small spalls are evidence of moving ground and are indications of potentially hazardous situations.
6.1.6.4 Observe the open side of the excavation to identify layered systems. Examine layered systems to identify if the layers slope toward the excavation and estimate the degree of slope of the layers.
6.1.6.5 Observe the sides of the excavation and adjacent areas for evidence of surface water or water seeping from the sides of the excavation.
6.1.6.6 Observe the area adjacent to the excavation and the area within the excavation for sources of vibration that may affect the stability of the excavation face.
6.1.7 Manual Test:
6.1.7.1 The thumb test (ASTM D2488) can be used to determine the unconfined compressive strength of cohesive soil. Type A soils with an unconfined compressive strength of 1.5 ton per square foot can be readily identified by the thumb. They can be penetrated by the thumb but only with great effort. Type C soils with an unconfined compressive strength of 0.5 ton per square foot can be easily penetrated several inches by the thumb and can be molded by light finger pressure.
6.1.7.2 Determine the unconfined compressive strength by the use of a pocket penetrometer.
7.0 APPENDICES
7.1 NCS Form 024 – Trenching and Excavation Initial Evaluation