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Layton City Policy

Personnel Policy Manual

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5005 - Trench Safety

  1. RESPONSIBILITIES

    1. Supervisors shall be responsible for:

      1. Providing all employees with information, training, and the equipment they need to protect themselves and others from excavation hazards.

      2. Ensuring compliance with this policy is met by all applicable employees.

      3. All appropriate employees presently employed and all new employees must be trained and responsible for the purpose and the use of this excavation safety policy.  Annual training will be provided.

    1. Employees shall be responsible for:

      1. Identifying and assessing the hazards of each excavation area.

      2. Understanding their assigned tasks relating to excavation safety.

      3. Applying the proper training and equipment to safely work in excavations and trenches.

      4. Assisting with the assessment and the identification of excavation hazards.

      5. Complying with the directives of this policy.

  2. DEFINITIONS

    An Excavation is any man-made cut, cavity, trench, or depression in the earth’s surface formed by earth removal.  Excavations produce unsupported soil conditions.

    A Trench is a narrow excavation made below the surface of the ground in which the depth is greater than the width.  The width does not exceed 15 feet.

    A Sloping System is a method of protecting employees from cave-ins by excavating to form sides of an excavation that are inclined away from the excavation so as to prevent cave-ins

    A Benching System is 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.

    An Aluminum Hydraulic Shoring is a pre-engineered shoring system comprised of aluminum hydraulic cylinders (cross braces) used in conjunction with vertical rails (uprights) or horizontal rails (walls).  Such system is designed specifically to support the sidewalls of an excavation and prevent cave-ins.

    A Cave-in is 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.

    A Competent Person is designated as someone 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.

    Distress means that the soil is in a condition where a cave-in is imminent or is likely to occur. It is evidenced by such phenomena as the development of fissures in the face of or adjacent to an open excavation; the subsidence of the edge of an excavation; the slumping of material from the face or the bulging or heaving of material from the bottom of an excavation; the spalling of material from the face of an excavation; and raveling, i.e., small amounts of material such as pebbles or little clumps of material suddenly separating from the face of an excavation and trickling or rolling down into the excavation.

    Faces or Sides are the vertical or inclined earth surfaces formed as a result of excavation work.

    Hazardous Atmosphere means an atmosphere which by reason of being explosive, flammable, poisonous, corrosive, oxidizing, irritating, oxygen deficient, toxic, or otherwise harmful, may cause death, illness, or injury.

    Protective System is 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.

    A Registered Professional Engineer is designated as a person who is registered as a professional engineer in the state where the work is to be performed.  However, a professional engineer, registered in any state is deemed to be a “registered professional engineer” within the meaning of this standard when approving designs for “manufactured protective systems” or “tabulated data” to be used in interstate commerce.

  3. HAZARDS

    The most common hazards that should be recognized and associated with work in excavations can be categorized as follows:

    Cave-in: Cave-ins are the most common excavation hazard.  They occur when a mass of soil or rock material separates from the side of an excavation or when soil is lost from under a trench shield or support system.  The mass of soil or rock material then moves suddenly into the excavation either by falling or sliding.  Cave-ins can entrap, bury, or otherwise injure and immobilize a worker.  Protective Support Systems such as sloping, benching, shielding, and shoring should be used to protect workers from cave-ins.

    Falls: Use warning systems such as mobile equipment, barricades, hand or mechanical signals, or stop logs to alert operators of the edge of an excavation.  Don’t let employees work on faces of sloped or benched excavations at levels above other employees unless the employees at lower levels are adequately protected.

    Equipment Accidents: Keep all equipment that might fall into an excavation at least 2 feet from the edge of the excavation.  Also, keep excavated soil at least 2 feet from the edge of the excavation.

    Water Accumulation: Employees are not to work in excavation areas where water has accumulated unless water removal equipment is being used.  Diversion ditches, dikes, or other means should be used to prevent surface water from entering an excavation and to provide drainage.

    Hazardous Atmospheres: Any excavation deeper than four feet or where an oxygen deficiency or a hazardous atmosphere exists or could exist needs to be checked by a competent person.  If hazardous conditions exist, respirators must be worn or ventilation must be provided and the atmosphere needs to be monitored.

    Access and Egress: If an excavation is deeper than four  feet, adequate means of exit, such as ladders, steps, ramps or other safe means of egress must be provided and be within 25 feet of the worker.  They must extend three feet above the ground.

    Overhead Power Lines: All equipment and employees must maintain at least 10 feet in distance from any overhead power line.  High voltage lines require 30 feet distance.  If for any reason this distance requirement is unable to be maintained; employees are required to stop work and notify a representative from the utility company.

  4. PRE-PLANNING

    Blue-Stake:  No employee is allowed to excavate without a valid, non-expired, Blue Stake Dig Number.  Utility companies or owners shall be contacted within the established or customary response times (typically 3 working days for non-emergency excavation), advised of the proposed work and asked to establish the location of the utility underground installation prior to the start of actual excavation.  If the excavator can no longer identify the location of the utilities due to fading, weather, construction or other reasons, the excavator is required to notify Blue Stakes before further excavation of the site.  In the event that a Blue Stake request area cannot be described over the phone, a Blue Stake meet shall be requested no less than two business days prior to the time of the meeting.  If utility companies or owners cannot respond to a request to locate underground utility installations within 48 hours (unless a longer period is required by state or local law), or cannot establish the exact location of these installations, the excavator may proceed, provided the excavator does so with caution, and provided detection equipment or other acceptable means to locate utility installations are used.  If damage to any utility is discovered or any suspicion of damage exists, it is the excavator’s responsibility to immediately notify the facility directly and take safety precautions to secure the work area.

    When excavation operations approach the estimated location of an underground installation a minimum clearance of 24 inches shall be maintained between an unexposed marked underground utility and the cutting edge of any power operated equipment.  If any excavation is required within 24 inches of any utility marking, the excavation shall be performed with extra care utilizing hand tools or vacuum excavation techniques.  While the excavation is open, underground installations shall be protected, supported or removed as necessary to safeguard employees.

    In order to ensure the safe execution of the trench excavation activities in the constructions site, the presence of a “Competent Person” shall be required during the activity.  A competent person shall be:

    Thoroughly knowledgeable in excavation safety standards, Occupational Safety and Health Administration’s (OSHA) Excavation and Trenching Standard 29 CFR 1926.650 to 1926-652, including soil classification.

    Capable of identifying existing and predictable hazards and unsafe conditions.

    Knowledgeable in the proper use of protective systems and trench safety equipment.

    Designated to have the authority to stop work when unsafe conditions exist.

    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.

    Before beginning any excavation, identify and evaluate specific job hazards.  These include, but are not limited to traffic, nearness of structures and their conditions, soil, surface and ground water, overhead, underground utilities, and weather.

    Pick the correct type of personal protective equipment for the job.  If the work-site is located near vehicular traffic, a warning vest or other suitable garments marked with or made of reflective or high-visibility material, hard hats, goggles, adequate foot wear and respirators will be worn.

  5. SOIL CLASSIFICATION

    Every soil and rock deposit needs to be classified by a competent person as stable rock, type A, type B, or type C before excavation can begin.  In a layered system, the system is classified according to its weakest layer.  Any time the properties, factors, or conditions affecting the soil type change in any way, the area needs to be reevaluated and reclassified to reflect the changed circumstances.

    Stable rock is natural solid mineral matter.

    Type A Soil: Classified as a cohesive soil with an unconfined, compressive strength of 1.5 tons per square foot or greater.  Examples of Type A soils are: clay, silty clay, sandy clay, clay loam.  Cemented soils such as caliche and hardpan and in some cases, silty clay loam and sandy clay loam.

    Soil will not be classified as Type A if:

    1. The soil is fissured.

    1. The soil is subject to vibration from heavy traffic, pile driving, or similar effects.

    1. The soil has been previously disturbed.

    1. The soil is part of a sloped, layered system where the layers dip into the excavation on a slope of four horizontal to one vertical or greater.

    1. The material is subject to other factors that would require it to be classified as a less stable material.

    The following excavations are recommended with this type of soil:

    All simple slope excavation 20 feet or less in depth shall have a maximum allowable slope of ¾:1.

    Exception:  Simple slope excavations which are open 24 hours or less (short term) and which are 12 feet or less in depth shall have a maximum allowable slope of ½:1

    All benched excavations 20 foot or less in depth shall have a maximum allowable slope of ¾ to 1 and maximum bench dimensions as follows:

    All excavations 8 feet or less in depth which have unsupported vertically sided lower portions shall have a maximum vertical side of 3 ½ feet

    All excavations more than 8 feet but not more than 12 feet in depth which unsupported vertically sided lower portions shall have a maximum allowable slope of 1:1 and a maximum vertical side of 3 1/2 feet.

    All excavations 20 feet or less in depth which have vertically sided lower portions that are supported or shielded shall have a maximum allowable slope of 3/4:1.  The support or shield system must extend at least 18 inches above the top of the vertical side.

    Type B Soil:

    1. Cohesive soil with an unconfined compressive strength greater than 0.5 tons per square foot, but less than 1.5 tons per square foot.

    2. Granular cohesionless soil including: angular gravel, silt, silt loam, sandy loam and, in some cases, silty clay loam and sandy clay loam.

    3. Previously disturbed soil except that which would otherwise be classed as Type C soil.

    4. Soil that meets the unconfined compressible strength or cementation requirements for Type A, but is fissured or subject to vibration.

    5. Dry rock that is not stable.

    6. Material that is part of a sloped, layered system where the layers dip into the excavation on a slope less steep that four horizontal to one vertical, but only if the material would otherwise be classified as Type B.

    The following excavations are recommended with this type of soil:

    All simple slope excavations 20 feet or less in depth shall have a maximum allowable slope of 1:1.

    All benched excavations 20 feet or less in depth shall have a maximum allowable slope of 1:1 and maximum bench dimensions as follows:

    All excavations 20 feet or less in depth which have vertically sided lower portions shall be shielded or supported to a height at least 18 inches above the top of the vertical side.  All such excavations shall have a maximum allowable slope of 1:1.

    Type C Soil:

    1. Cohesive soil with an unconfined compressive strength of 0.5 tons per square foot or less.

    2. Granular soil including gravel sand and loamy sand.

    3. Submerged soil or soil from which water is freely seeping.

    4. Submerged rock that is not stable.

    5. Material in a sloped, layered system where the layers dip into the excavation or a slope of four horizontal to one vertical or steeper.

    The following excavations are recommended with this type of soil:

    All simple slope excavations 20 feet or less in depth shall have a maximum allowable slope of 1 1/2:1.

    All excavations 20 feet or less in depth which have vertically sided lower portions shall be shielded or supported to a height at least 18 inches above the top of the vertical side.  All such excavations shall have a maximum allowable slope of 1 1/2:1.

  6. SOIL TESTING

    1. Classification tests of soil shall be performed by a competent person using at least one visual test and one manual test.

    1. Visual tests provide qualitative information on the excavation site in general, the soil adjacent to the excavation, the soil forming the sides of the open excavation, and the soil taken as samples from the excavated material.  To perform a visual test:

      1. Observe samples of soil and estimate the range of particle sizes and their relative amounts.  Soil that is primarily composed of fine-grained material is cohesive material.  Soil composed primarily of coarse-grained sand or gravel is granular material.

      2. Observe soil as it is excavated.  Soil that remains in clumps is cohesive and soil that breaks up easily is granular.

      3. Observe the side of the opened excavation and the adjacent surface.  Crack-like openings, tension cracks, and chunks of soil that spall off a vertical side could indicate fissured material.  Small spalls are evidence of moving ground and are potentially hazardous.

      4. Observe the surrounding area and the excavation area itself for existing utility and other underground structures, and to identify previously disturbed soil.

      5. Observe the sides of the excavation for layered systems.

      6. Observe the excavation area for evidence of surface water, water seeping from the sides of the excavation, or the level of the water table.

      7. Observe the excavation area for sources of vibration that may affect the stability of the excavation face.

    2. Manual tests provide quantitative as well as qualitative properties of soil.  They provide more information in order to classify the soil properly.  Some examples of manual tests include:

      1. Dry strength

      2. Thumb penetration

  7. JOB SITE SAFETY

    Employees working in area where there exists a danger of head injury due to falling or flying objects shall be provided with and wear hard hat, safety glasses and gloves.  When exposed to public vehicular traffic shall be provided with, and shall wear warning vests or other suitable garments marked with or made of reflective or high-visibility material.

    No employee shall be permitted underneath loads handled by lifting or digging equipment.  Employees shall be required to stand away from any vehicle being loaded or unloaded to avoid being struck by any spillage or falling materials.  Employees shall be protected from excavated or other materials or equipment that could pose a hazard by falling or rolling into excavations.  Protections shall be provided by placing and keeping such materials or equipment at least 2 feet from the edge of excavations, or by the use of retaining devices that are sufficient to prevent materials or equipment from falling or rolling into excavations, or by a combination of both if necessary.

    Each employee in an excavation shall be protected from cave-ins by use of an adequate sloping, benching, trench box or shoring device, hereafter referred to as protective system.  All employees engaged in excavation activities shall be trained and understand the relevant OSHA standards during excavation. 

    The walls and faces of all excavations in which employees are exposed to danger from moving ground shall be guarded by a shoring system, sloping of the ground, or some other equivalent means.  (29CFR 1926.651(c)

    Sides of trenches in unstable or soft material, 5 feet or more in depth, shall be shored, sheeted, braced, sloped or otherwise supported by means of sufficient strength to protect employees working within them.  (29 CFR 1926.652(b)

    Excavations (including trenches) adjacent to backfilled areas or subjected to vibrations from railroads, highway traffic, or operation of machinery shall have additional shoring and bracing precautions taken.  (29 CFR 1926.651 (m) and 1926.652(e)

    Excavations from 5 feet to 24 feet deep in Type A and Type B soils or 5 feet to 15 feet in type C soil shall be: provided with a shoring system capable of supporting the lateral soil pressure, cut back to the steepest allowable slope for the type of soil, or a combination of both measures.  Stable rock is exempt. 

    Excavations deeper than 24 feet, except those in unfractured rock, an engineer shall determine shoring, shielding, or sloping requirements.

    Sloping and Benching Systems

    A sloping system means a method of protecting employees from cave-ins by excavating to form sides of an excavation that are inclined away from the excavation so as to prevent cave-ins.

    The angle of incline required to prevent a cave-in varies with differences in such factors as the soil type, environmental conditions of exposure, and application of surcharge loads.

    The maximum allowable slope means the steepest incline of an excavation face that is acceptable

    for the most favorable site conditions as protection against cave-ins, and is expressed as the ratio of horizontal distance to vertical rise (H:V).  This varies according to the soil type which can be classified by a competent person.

    The actual slope shall never be steeper than the maximum allowable slope.  When there are signs of distress, 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.

    A benching system means 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.

    The length of the vertical sides of a benching system and the maximum allowable slope required to prevent a cave-in varies with differences in such factors as the soil type, environmental conditions of exposure, and application of surcharge loads.

    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.  Manufactured materials and equipment used for protective systems shall be used and maintained in a manner that is consistent with the recommendations of the manufacture and in a manner that will prevent employee exposure to hazards.

    Shielding Systems

    A shielding system is a pre-constructed structure that is able to withstand the forces imposed on it by a cave-in and thereby protect employees within the structure.  Shielding used in trenches are usually referred to as trench boxes or trench shields.  Shielding can be permanent structures or can be designed to be portable and moved along as work progresses.  Shielding must extend above the ground level or the trench walls above the top of the box must be sloped.

    Shoring Systems

    A shoring system means 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. Shoring systems shall be installed from the top down and removed from the bottom up.  Unless they are installed and removed from outside the trench.

    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, the material or equipment shall be removed from service and shall be evaluated and approved by a registered professional before being returned to service.  Parts of protective system shall be securely connected together to prevent sliding, falling, kick-outs or other predictable failure.  Protective systems shall be installed and removed in a manner that protects employees from cave-ins, structural collapse or from being struck by parts from the protective system. 

    Excavation of material to a level no greater than two feet below the bottom of the protective system support shall be permitted, but only if the system is designed to resist the forces calculated for the full depth of the trench and there are no indications while the trench is open of the possible loss of soil from behind or below the bottom of the protective system support.  Installation of a protective system shall be closely coordinated with the excavation of trenches.  Employees shall not be allowed in shields when protective systems are being installed, removed or moved vertically.  

    A stairway, ladder, ramp or other safe means of egress shall be located in trench excavations that are four feet or more in depth so as to require no more than 25 feet of lateral travel for employees.  Ladders must extend a minimum of three feet above the excavation.

    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.

    Employees shall not work in excavations in which there is accumulated water.  Water shall be controlled or prevented from accumulating by the use of removal equipment.  Use of removal equipment shall be monitored at all times by a competent person to ensure proper operation of the equipment.  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

    Adequate precautions shall be taken to prevent any employee exposure to atmospheres containing less than 19.5 percent oxygen.  Precaution shall also be taken to prevent employee exposure to an atmosphere containing a concentration of a flammable gas in excess of 20 percent of the lower flammable limit of gas.  Atmosphere in the excavation shall be tested before entry by employees.  Where oxygen deficiency or any hazardous atmosphere exists or could reasonably be expected to exist, adequate precautions shall be taken.  These precautions may include providing respiratory protection or ventilation.  When controls are used that are intended to reduce the level of atmospheric contaminants to acceptable levels, continuous monitoring shall be conducted to ensure the atmosphere remains safe.

    Traffic Control Procedures

    Work zones within the roadway system must use approved traffic control devices to move vehicles and pedestrians safely and expeditiously through or around work zones while protecting on-site workers and equipment as outlined in the Manual on Uniform Traffic Control Devices.

  8. EMERGENCIES

    If you are about to be buried in a cave-in:

    1. Yell to get attention
    2. Cover your face with your arms.
    3. Do not struggle to free yourself, just wait calmly for rescue.

    If you are watching someone about to be buried in a cave-in:

    1. Do not attempt to rescue them yourself.  Never enter the excavation.

    2. Notify the Fire Department by calling 911 on your radio or phone.  Give the emergency personal information about the exact location of the accident, the number of victims involved, the trench measurements, and special hazard information.

    3. Shut down all heavy equipment and move other workers away from the area.

    4. Monitor the situation until fire rescue personnel arrive.

  9. BACK-FILLING

    Fill the excavated area as soon as you are done working in that area ensuring Layton City Compaction Standards are met.  Backfill materials shall not be pushed or dumped into an excavation while an employee is still in it.  At the completion of a backfill operation, excess fill and other debris should be completely cleaned up, especially on paved roads.

                        Enacted, 1/28/2011, Previous Policy 5005
                         




                         
                         
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