Quality. Integrity. Experience. Electrical Engineers and Contractors Since 1918 Specializing in Design/Build TRENCHING AND EXCAVATION PROGRAM Procedures Training Protective Support Systems
PURPOSE The purpose of this policy is to protect all workers from injuries while working in or around trenches and excavations, to prevent property damage to underground utilities, and to comply with Federal OSHA CFR 1926.650 Subpart P Excavations. POLICY Trenching less than four feet: Staff Electric may self perform trenching work less than four feet using a mini backhoe (rental) or trenching attachment to a skid steer. Only qualified and trained people shall operate trenching equipment. Trenching greater than four feet: Subcontractors shall be used for trenches and excavations greater than four feet deep. Subcontractors shall have a current signed subcontract agreement and certificate of insurance before issuing them a purchase order. Check the pre-qualified subcontractor list for subcontractors already completing this process. Contact the Safety Department for issuing a site specific subcontract agreement to subcontractors currently not on the pre-qualified list. WORKING NEAR UNDERGROUND UTILITIES: No trenching or excavating work shall begin without a current underground locate. The person/company operating the trenching/excavating equipment must be the one to call for the locate. Another company such as Staff Electric, shall not call for a locate in place of the equipment operator. Hand digging is required when trenching or excavating within 18 inches of either side of an underground locate marking. Never make any assumptions regarding the depth of the underground utility. Always proceed as if the utility is located just beneath the ground surface. When poor soil situations exist thereby making hand digging difficult or ineffective, hydro-excavating is a safe and effective alternative to hand digging. Contact the Project Manger and Safety Director for assistance with evaluating hydro-excavating needs. RESPONSIBILITIES The foreman supervising the trenching and excavating work is designated the competent person. The foremen have been trained to identify existing and predictable hazards in the surroundings or work conditions which are hazardous to employees and who has the authorization to take prompt corrective measures to eliminate them. The foreman is expected to immediately stop work and correct any hazardous situations. The equipment operator is also expected to be the competent person on site. The equipment operator must be trained in soil testing and protective systems. The equipment operator is required to complete a visual and manual soil classification test when work begins and whenever conditions change. The foreman is responsible for verifying that the equipment operator is trained (competent person training card) and completes the soil classification tests. Staff Electric Company, Inc. Trenching and Excavation Safety 2
It is the policy of Staff Electric to permit only trained and authorized personnel to create or work in excavations. These procedures are applicable to all employees including those who only occasionally work in excavations. BEFORE EXCAVATING Before excavation begins, it is standard procedure to: 1. Contact the utility companies (i.e. Diggers Hotline) or property owners to determine the exact location of the underground installations in the area. Generally, this requires at least 3 days prior notice. 2. Remove or adequately support objects in the excavation area that could create a hazard to employees. These may include trees, rocks, sidewalks, and other objects. 3. Classify the type of soil and rock deposits at the site as either stable rock, Type A, Type B, or Type C soil. The soil classification is based on the results of at least one visual and at least one manual analysis conducted by a competent person. The competent person has enough training to identify soil types and other excavation hazards and has the authority to take prompt corrective action. (Note: Soil classification is not necessary if the excavation will be sloped to an angle of one and one-half horizontal to one vertical). 4. The Site Supervisor is required to choose the appropriate method of protective systems, as necessary. Sloping or benching for excavations greater than 20 feet deep shall be designed by a registered professional engineer. SOIL TESTING Soil that has not been disturbed is kept in place by horizontal and vertical forces. In a trench or excavation, soil will naturally move downward and inward, causing a potentially life threatening situation for any worker. Soil can weigh 100-145 pounds per cubic foot. With the suction effect, pulling out one buried worker s foot can take 750 pounds of force. Soils are classified into the following 4 types: Soil Type A Most stable: clay, silty clay and hardpan (resists penetration) Soil Type B Medium stability: silt, sandy loam, medium clay and unstable dry rock Soil Type C Least stable: gravel, loamy sand, soft clay, submerged soil or dense, heavy unstable rock Stable Rock When a competent person makes a site soil classification, several soil qualities are assessed in addition to the type. Those qualities are grain size, saturation, cohesiveness and unconfined compressive strength. If a grain of soil is larger than pencil lead, it s gravel. If it s smaller, it s sand. The naked eye can not see particles of clay and silt. Staff Electric Company, Inc. Trenching and Excavation Safety 3
There are four different grain sizes: Gravel Sand Silt Clay In general, the bigger the grains, the less stable the soil and the more careful you need to be. Saturation refers to how much water is in the void between the grains. When voids fill with water, soil is saturated. When voids fill with air, the soil is oven dry. A certain amount of water makes the soil stable, but too much or too little, water causes cave-ins. Cohesion, or stability, refers to how well the grains hold together. It predicts how well the trench wall will hold together and whether or not trench protection is required. Unconfined compressive strength refers to how soil reacts under pressure, as measured by the amount of weight per square foot required to collapse a sample. How Soil is Tested To classify soil, a competent person will conduct both visual and manual tests. Visual Testing Clues Look at soil particle size and type. There will be a mixture of different types. Does the soil clump when dug? It could be clay or silt. Cracks in walls and spalling can mean soil types B or C. Layered systems with adjacent hazardous areas buildings, roads and vibrating machinery may require a professional engineer for classification. Standing water or water seeping through trench walls automatically means soil type C. Manual Testing Manual soil tests are required before a protective system is selected. A sample taken from soil dug out from a spoil pile is tested as soon as possible to preserve its natural moisture. Soil can be tested either on site or off site. Manual tests include: Sedimentation Test determines how much silt and clay are in sandy soil. Saturated sandy soil is placed in a straight-sided jar with about five inches of water. After the sample is thoroughly mixed and allowed to settle, the percentage of sand is visible. Using this data, the soil is classified. For example, a sample with 80% sand will be classified Type C. Water Shaking Test is another way to determine the amount of sand versus clay and silt in a solid sample. In your hand, shake a saturated sample to gauge soil permeability based on the following facts: - Shaken clay resists water movement through it - Water flows freely through sand and less freely through silt. Staff Electric Company, Inc. Trenching and Excavation Safety 4
RopeThread Test determines cohesion. A representative soil sample is rolled between the palms of the hands to 1/8 diameter and several inches in length. The rolled piece is placed on a flat surface, then picked up. If a sample holds together for two inches, it s considered cohesive. Ribbon Test determines cohesion and is used as a backup for the Thread Test. A representative soil sample is rolled out (using the palms of the hands) to ¾ in diameter, and several inches in length. The sample is squeezed between the thumb and forefinger into a flat unbroken ribbon 1/8 to ¼ thick, which is allowed to fall freely over the fingers. If the ribbon does not break off before several inches are squeezed out, the soil is considered cohesive. Thumb Penetration Test provides a simple determination to identify soil type. Type A soils with an unconfined compressive strength of 1.5 tsf can be indented by the thumb only with great effort. Type C soils with an unconfined compressive strength of 0.5 tsf can be easily penetrated several inches by the thumb, and can be molded by light finger pressure. This test should be conducted on an undisturbed soil sample, such as a large clump of spoil, as soon as practiceable after the excavation. PROTECTIVE SUPPORT SYSTEMS Staff Electric has developed the following standard operating procedures regarding protective support systems for excavations, in accordance with safe practices and procedures and OSHA excavation regulations. 1. Each employee in an excavation is protected from cave-ins during an excavation by an adequate protective system designed in accordance with OSHA standards. Protective system options include proper sloping or benching of the sides of the excavation; supporting the sides of the excavation with timber shoring or aluminum hydraulic shoring; or placing a shield between the side of the excavation and the work area. The Site Supervisor chooses the most practical design approach for the particular circumstance. The system approach selected will meet the required performance criteria. 2. No protective system is necessary if the excavation is made entirely in stable rock, or the excavation is less than 5 feet (1.52 m) in depth (provided there is no indication of a potential cave-in. 3. Protective systems for use in excavations more than 20 feet in depth must be designed by a registered professional engineer. SLOPING AND BENCHING 1. When sloping or benching is used to protect against cave-in, there are four basic options that can be chosen for designing sloping or benching systems. First, if soil classification is not made, then the sides of the excavation can be sloped to an angle Staff Electric Company, Inc. Trenching and Excavation Safety 5
2. The second option for designing a sloping or benching system is to use Appendices A and B of the excavation standard for sloping and benching systems. These requirements are summarized in Table 1 in the Appendix. The soil type must be determined in order to use this option. 3. Sloping and benching systems can also be designed using other tabulated data approved by a registered professional engineer or by having an engineer design and approve the system to be used. 4. The Site Supervisor will choose the best option for sloping and benching for the job at hand. 5. There are a number of exceptions or special cases to these general sloping and benching guidelines, which will be utilized by the Site Supervisor if the conditions meet the exception s requirements. The exceptions and conditions are outlined below: In Type A soil, simple slope excavations which are open 24 hours or less (short term) and which are 12 feet high or less in depth may have a maximum allowable slope of ½ horizontal to 1 vertical. In Type A soil, all excavations 8 feet or less in depth which have unsupported vertically sided lower portions must have a maximum vertical side of 3.5 feet. In Type A soil, excavations over 8 feet but less than 12 feet in depth with unsupported vertically sided lower portions must have a maximum allowable slope of 1H:1V and a maximum vertical side of 3.5 feet. In Type A soil, excavations 20 feet or less with vertically sided lower portions that are supported or shielded shall have a maximum allowable slope of 3/4H:1V. The support or shield system must extend at least 18 inches above the top of the vertical side. In Type B soil, all excavations 20 feet or less 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. The excavations shall have a maximum allowable slope of 1H:1V. In Type C soil, all excavations 20 feet or less which have vertical sided lower portions shall be shielded or supported to a height at least 18 inches above the top of the vertical side. The excavation shall have a maximum allowable slope of 1-1/2H:1V. 6. When an excavation contains layers of different types of soils, the general sloping requirements do not apply. The excavation must be sloped according to Table 2 in the Appendix. Staff Electric Company, Inc. Trenching and Excavation Safety 6
Timber Shoring 1. Designs for timber shoring in trenches for company work sites are determined using one of four methods: using the requirements set forth by OSHA in Appendices A and C of the excavation standard; using data provided by the manufacturer of the support system; using other tabulated data approved by an engineer; or having a registered professional engineer design the system. The Site Supervisor chooses from among these options. 2. OSHA design specifications apply only to trenches that do not exceed 20 feet. The soil type in which the excavations is made must be determined in order to use the OSHA data. The specifications do not apply in every situation experienced in the field; the data were developed to apply to most common trenching situations. If the specifications do not apply to the situation encountered in the field, the Site Supervisor will make a determination of what approach to use to allow safe protective support of the excavation. Aluminum Hydraulic Shoring 1. Designs for aluminum hydraulic shoring are based upon manufacturer s tabulated data and are in accordance with the manufacturer s specifications, recommendations and limitations. Deviations from the manufacturer s specifications, recommendations or limitations are only allowed upon written approval of the manufacturer, which must be obtained by the Site Supervisor prior to implementation. The written approval is kept at the job site during construction of the protective system. 2. If the manufacturer s tabulated data cannot be utilized, the aluminum hydraulic shoring is designed using the OSHA specifications found in Appendix D of the excavation standard. Before using the OSHA data, the soil type must be determined. Other options for the design of aluminum shoring systems include using other tabulated data approved by an engineer or having a registered professional engineer design the system. Again, the Site Supervisor determines the best choice for the situation. GENERAL REQUIREMENTS FOR EXCAVATIONS The following rules are to be followed at all times by all employees working on, in or near excavations, as applicable: 1. Employees exposed to public vehicular traffic must wear warning vests or other suitable garments made of reflective or high-visibility material. 2. The foreman on site will be the competent person for that site unless other provisions for a competent person are made. 3. The foreman on site is responsible for site security, traffic and pedestrian control, emergency situation decisions, site safety implementation and communications. 4. It is the responsibility of the foreman to contact the main office in any emergency situation. 5. The Competent Person inspects the excavation and the adjacent areas on a daily basis for possible cave-ins, failure of protective systems and equipment, hazardous Staff Electric Company, Inc. Trenching and Excavation Safety 7
6. All personnel MUST remain away from edges of open excavations except when entering or exiting. The need for a warning line system to alert operators of heavy equipment and other employees of the edge of an excavation will be determined on a job specific basis. 7. Measures to protect employees from falling rock, soil, or other materials and equipment will be provided. Protection will be provided by placing and maintaining materials or equipment at least 2 feet from the edge of the excavation, or by the use of retaining devices that are sufficient to prevent materials or equipment from falling or rolling into excavations. 8. Employees are not permitted under loads that are handled by lifting or digging equipment. Employees are not allowed to work in the excavation above other employees unless the lower level employees are adequately protected. 9. While the excavation is open, underground installations must be protected, supported or removed as necessary to safeguard employees. Adjacent structures must be supported to prevent possible collapse. 10. Employees are not permitted to work in excavations where water has accumulated or is accumulating. Diversion ditches, dikes or other means must be used to prevent surface water from entering an excavations and to provide drainage to an adjacent area. 11. Before an employee enters an excavation greater than 4 feet in depth, the Site Supervisor or other competent person must test the atmosphere where oxygen deficiency or a hazardous atmosphere exists or could reasonable exist. When air monitoring is required, Staff Electric s Confined Space policy must be followed. Emergency rescue equipment must be readily available and attended when hazardous atmospheric conditions exist or may develop. 12. ONLY trained Rescue personnel should attempt to rescue employees trapped in a cave-in or excavation failure. 13. Sufficient means for exiting excavations 4 feet deep or more must be provided and must be within 25 feet of lateral travel for employees. 14. Guardrails will be provided if there are walkways or bridges crossing over an excavation. TRAINING Under no circumstances shall an employee be allowed into an excavation unless he/she has been properly trained on trenching safety. Under no circumstances shall an employee be allowed to make an excavation 4 feet deep or more until he/she has completed Staff Electric s excavation training program. The training program includes classroom instruction and hands-on training on each specific type of protective support system to be implemented by the employee in his-her work area. Staff Electric Company, Inc. Trenching and Excavation Safety 8
Classroom training consists of: 1. Review of handbook by employee. 2. Review of safety training video. Protective support system training consists of hands-on instruction in design, and use of the protective support systems which the employee will be implementing in excavations. Staff Electric Company, Inc. Trenching and Excavation Safety 9
TABLE 1 MAXIMUM ALLOWABLE SLOPES SOIL OR ROCK TYPE MAXIMUM ALLOWABLE SLOPES (H:V) 1 FOR EXCAVATIONS LESS THAN 20 FEET DEEP STABLE ROCK VERTICAL (90) TYPE A ¾ : 1 (53) TYPE B 1:1 (45) TYPE C 1 ½ : 1 (34) Notes: 1. Numbers shown in parentheses next to maximum allowable slopes are angles expressed in degrees from the horizontal. Angles have been rounded off. 2. A short-term maximum allowable slope of 1/2H:1V (63) is allowed in excavations in Type A soil that are 12 feet (3.67m) or less in depth. Short term maximum allowable slopes for excavations greater than 12 feet (3.67m) in depth shall be 3/4H:1V (53). 3. Sloping or benching for excavations greater than 20 feet deep shall be designed by a registered professional engineer. TABLE 2 Sloping Requirements for Layered Soils Slope Required for Each Soil Layer Layered Soil Type Type A Layer Type B Layer Type C Layer B over A ¾:1 1:1 C over A ¾:1 1 ½:1 C over B 1:1 1 ½:1 A over B 1:1 1:1 A over C 1 ½:1 1 ½:1 B over C 1 ½:1 1 ½:1 Staff Electric Company, Inc. Trenching and Excavation Safety 10
Slope Configurations 1. All simple slope excavations 20 feet or less in depth shall have a maximum allowable slope of ¾:1. 2. Simple Slope Short Term 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. 3. All excavations 8 feet or less in depth which have unsupported vertically aided lower portions shall have a maximum vertical side of 3 ½ feet (Example Type A soil). Staff Electric Company, Inc. Trenching and Excavation Safety 11