Excavation Safety. Basic

Transcription

1 Excavation Safety Basic This course introduces the student to the safety hazards, precautions, and requirements within OSHA 1926, Subpart P, Excavations. This course provides general information about the hazards, protective systems, and safe work practices related to working in excavations and trenches.

2 This page intentionally blank

3 OSHAcademy Course 157 Study Guide Excavation Safety: Basic Copyright 2018 Geigle Safety Group, Inc. No portion of this text may be reprinted for other than personal use. Any commercial use of this document is strictly forbidden. Contact OSHAcademy to arrange for use as a training document. This study guide is designed to be reviewed off-line as a tool for preparation to successfully complete OSHAcademy Course 157. Read each module, answer the quiz questions, and submit the quiz questions online through the course webpage. You can print the post-quiz response screen which will contain the correct answers to the questions. The final exam will consist of questions developed from the course content and module quizzes. We hope you enjoy the course and if you have any questions, feel free to or call: OSHAcademy NW Greenbrier Parkway, Suite 230 Beaverton, Oregon instructor@oshatrain.org +1 (888) Disclaimer This document does not constitute legal advice. Consult with your own company counsel for advice on compliance with all applicable state and federal regulations. Neither Geigle Safety Group, Inc., nor any of its employees, subcontractors, consultants, committees, or other assignees make any warranty or representation, either express or implied, with respect to the accuracy, completeness, or usefulness of the information contained herein, or assume any liability or responsibility for any use, or the results of such use, of any information or process disclosed in this publication. GEIGLE SAFETY GROUP, INC., DISCLAIMS ALL OTHER WARRANTIES EXPRESS OR IMPLIED INCLUDING, WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Taking actions suggested in this document does not guarantee that an employer, employee, operator or contractor will be in compliance with applicable regulations. Ultimately every company is responsible for determining the applicability of the information in this document to its own operations. Each employer s safety management system will be different. Mapping safety and environmental management policies, procedures, or operations using this document does not guarantee compliance regulatory requirements.

4 This page intentionally blank

5 Contents Modules and Learning Objectives... 1 Course Introduction... 3 Module 1: The Hazards... 4 Excavation vs. Trench... 4 How Cave-ins Occur... 5 Common Soil Problems... 5 Soil Mechanics... 5 Tension Cracks... 6 Sliding or Sluffing... 6 Heaving or Squeezing... 7 Boiling... 7 Unit Weight of Soils... 7 Sliding Problems... 8 Soil Testing... 9 Soil and Stability... 9 Visual Tests Manual Tests Manual Test Examples Competent Person Module 2: Protection Systems Pre-Job Planning Protective Systems Other Safety Precautions... 14

6 Installation and Removal of Protective Systems Appropriate Protective System Designs Method 1: Sloping Method 2: Design Using Data Method 3: Trench Box or Shield Benching Shoring Types Hydraulic Shoring Pneumatic Shoring Other Protective Systems Ingress and Egress Additional Hazards and Protections Additional Resources... 22

7 Modules and Learning Objectives Module 1 The Hazards Learning objectives in this module include: Describe the difference between an excavation and a trench. Describe some common soil problems that create hazards in excavations. Describe soil mechanics causing tension cracks, slide or sluffing, and heaving or squeezing. Discuss how soil is weighed and how soil weight is a major hazard for excavation workers. Describe the differences among Type A, B, and C soils in terms of stability. Describe the various visual and manual soil testing methods. Discuss the role of and requirements for the excavation competent person. Module 2 Protection Systems Learning objectives in this module include: Describe the importance of completing pre-job planning activities. Describe the three primary protection methods: sloping, shoring, and shielding, and give examples. Briefly describe the steps in installing and removal of protective systems. Discuss the design requirements for sloping and shoring, the use of data, and trench boxes. Discuss the design requirements for benching. Describe the use of hydraulic and pneumatic shoring systems. Discuss the requirements for safe ingress into and egress from excavations. Copyright 2018 Geigle Safety Group, Inc. Page 1 of 22

8 Discuss various additional safety precautions for workers while working in the excavation. Copyright 2018 Geigle Safety Group, Inc. Page 2 of 22

9 Course Introduction Excavation and trenching are among the most hazardous construction operations. OSHA's standard, 1926, Subpart P, Excavations, contains requirements for excavation and trenching operations. Proper trenching operations are necessary to protect the workers from soil collapse. The basic trenching operations that help make a trench safe for workers are described and illustrated in this course. The methods of shoring installation are also discussed briefly. This course is not intended to be used as a step-by-step guideline in the excavation process. This course highlights methods for protecting employees against cave-ins, and describes safe work practices for employees. A necessary first step in planning the approach to any trenching or other excavation project is to understand what could go wrong. This understanding can help avoid many of the problems associated with excavation. This course is also not intended to be a guideline for compliance with all pertinent OSHA regulations, but rather an overview of safe practices in trenching operations. Though the course is not intended to be inconsistent with OSHA standards, if an area is considered by the reader to be inconsistent, the OSHA standard should be followed. Copyright 2018 Geigle Safety Group, Inc. Page 3 of 22

10 Module 1: The Hazards Trenching and excavation work presents serious hazards to all workers involved. Cave-ins pose the greatest risk and are more likely than some other excavation-related incidents to result in worker fatalities. One cubic yard of soil can weigh as much as a car. Employers must ensure that workers enter trenches only after adequate protections are in place to address cave-in hazards. Other potential hazards associated with trenching work include falling loads, hazardous atmospheres, and hazards from mobile equipment. Excavation vs. Trench Dig a hole in the ground and you've made an excavation. Excavations can be any size: wide, narrow, deep, or shallow. A trench is a narrow excavation, not more than 15 feet wide at the bottom. If you install forms or other structures in an excavation that reduce its width to less than 15 feet, measured at the bottom, the excavation is also considered a trench. If you work in an excavation that's five feet deep (or deeper) you must be protected from a cave-in. If a competent person, who has training in soil analysis, determines that there's a potential for an excavation to cave-in, you must be protected regardless of its depth. Quiz Instructions After each section, there is a quiz question. Make sure to read the material in each section to discover the correct answer to these questions. Circle the correct answer. When you are finished go online to take the final exam. This exam is open book, so you can use this study guide. 1. A is not more than 15 feet wide at the bottom. a. channel b. ditch c. excavation d. trench Copyright 2018 Geigle Safety Group, Inc. Page 4 of 22

11 How Cave-ins Occur Undisturbed soil stays in place because opposing horizontal and vertical forces are evenly balanced. When you create an excavation, you remove the soil that provides horizontal support. Soil will eventually move downward into the excavation. The longer the face (a side of the excavation) remains unsupported, the more likely it is to cave in. Common Soil Problems The terms soil and earth are commonly referred to in the excavation process to describe the naturally occurring materials uncovered on a project. Soil conditions vary from one site to the next. Soil may be loose or partially cemented, organic or inorganic. However, most soils can be referred to as a mixture or an accumulation of mineral grains that are not cemented together. An exception is hard rock, which remains firm after exposure to the elements. Soil failure is defined as the collapse of part or all of an excavation wall. The most common soil failure is typically described as an unexpected settlement, or cave-in, of an excavation. Soil sliding is the most common factor leading to soil failure. Proper planning and supervision can avoid the unsafe working conditions caused by soil sliding. Unless such safety precautions have been implemented, sliding soil failure can occur in all types of excavations (including sloped trenches and excavations with braced trench boxes). 2. In an excavation, what is the most common factor leading to soil failure? a. Tension cracks b. Soil sliding c. Boiling d. Prior disturbance Soil Mechanics A number of stresses and deformations can occur in an open cut or trench. For example, increases or decreases in moisture content can adversely affect the stability of a trench or excavation. The following diagrams show some of the more frequently identified causes of trench failure. Copyright 2018 Geigle Safety Group, Inc. Page 5 of 22

12 Tension Cracks Tension cracks usually form at a horizontal distance of one-half to three-quarters times the depth of the trench, measured from the top of the vertical face of the trench. Sliding or Sluffing Copyright 2018 Geigle Safety Group, Inc. Page 6 of 22

13 This may occur as a result of tension cracks. 3. Tension cracks usually form at a horizontal distance of. a. twice the depth of the trench b. one-half to three-quarters times the depth of the trench c. within one foot of the vertical face of the trench d. about twice the width or one-half the height of the trench Heaving or Squeezing Bottom heaving or squeezing is caused by the downward pressure created by the weight of adjoining soil. This pressure causes a bulge in the bottom of the cut, as illustrated below. Heaving and squeezing can occur even when shoring or shielding has been properly installed. Boiling Boiling is evidenced by an upward water flow into the bottom of the cut. A high-water table is one of the causes of boiling. Boiling produces a quick condition in the bottom of the cut and can occur even when shoring or trench boxes are used. 4. What causes bottom heaving or squeezing in a trench? a. Downward pressure created by the weight of adjoining soil b. Upward movement of the soil due to loss of downward pressure c. A high-water table causes upward movement of trench base d. A lack of downward pressure from directly above Unit Weight of Soils This refers to the weight of one unit of a particular soil. The weight of soil varies with type and moisture content. One cubic foot of soil can weigh from 110 pounds to 140 pounds or more, and one cubic meter (35.3 cubic feet) of soil can weigh more than 3,000 pounds. A safe slope can be defined as the maximum angle of the edge wall or bank of an excavation at which sliding will not occur. The unique mixtures of the different types of soil (sand, clay, silt and rock) necessitate different safe slopes from one excavation site to the next. There are other complicating factors that can result in sliding soil failures. During an excavation, visibly different layers of soil may be uncovered. Each of those layers may call for different safe slopes. It is essential to plan your excavation around the most gradual (rather than steepest) safe slope for all of the different soil types and layers encountered during the excavation. Copyright 2018 Geigle Safety Group, Inc. Page 7 of 22

14 Another complicating factor is that soil composition mixtures may vary significantly from one area of the project to another. During an excavation, as the soil composition changes, the safe slope for trench wall excavation also changes. Thus, across an excavation site, the slope of the bank may need to be different to provide a safe working environment. 5. One cubic foot of soil can weigh, and one cubic meter of soil can weigh. a. up to 100 pounds, as much as 500 pounds b. 100 pounds, up to 1,500 pounds c. 140 pounds or more, more than 3,000 pounds d. 280 pounds, around 2,000 pounds Sliding Problems Sliding and other modes of failure can also occur in soils that are not densely compacted. For example, a trench that is made close to a previously dug trench is very unstable. If noncompacted soil is discovered, the normal safe slope for dense soil will not be enough to prevent sliding. Bracing or further sloping may be necessary. If cracks are observed in rocky types of soil, sliding has already occurred. These cracks should signal that a more gradual slope for excavation is needed because the rocky soil is very susceptible to slides and other types of failure. Excavations that have been stable for long periods are also subject to sliding types of failure. After prolonged exposure to the elements, the moisture content in the soil may increase. This increase in moisture may be due to various causes, such as rainfall or a broken water line. The extra soil moisture tends to speed up sliding soil failures. Determining the correct safe slope can be quite difficult for certain types of soil. The OSHA standard has developed a simple method of determining safe excavation bank slopes for different soil types. This method will be discussed in more detail in a later section of this document. Soil failure can occur for any number of reasons. Factors that increase the chances of soil failure are: 1. excessive vibration - heavy equipment movement, earthquakes 2. surface encumbrances - obstructions, broken water lines Copyright 2018 Geigle Safety Group, Inc. Page 8 of 22

15 3. weather conditions - prolonged periods of rain 6. Each of the following is a factor that increases the chance of soil failure, EXCEPT. a. excessive vibration b. compaction c. surface encumbrances d. weather conditions Soil Testing A competent person must conduct visual and manual soil tests before anyone enters an excavation. Visual and manual tests are a critical part of determining the type of protective system that will be used. Soil and Stability Some soils are more stable than others. The type of soil is one of the factors that determine the chance that an excavation will cave in. There are three basic soil types that you may encounter: Type A very stable. Clay is an example. Type B less stable than type A soil. The soil will crack or fissure. Crushed rock, silt, and soils that contain an equal mixture of sand and silt are examples. Type C the least stable soil. Particles do not stick together. Gravel and sand are examples. Soil has other qualities that affect its stability. These include granularity, saturation, cohesiveness, and unconfined compressive strength. Granularity refers to the size of the soil grains; the larger the grains, the less stable the soil. Saturation means how much water soil will absorb. Cohesiveness means how well soil holds together; clay is a cohesive soil. Unconfined compressive strength is determined by a test that shows how much pressure it takes to collapse a soil sample. For example, type A soil must have an unconfined compressive strength of at least 1.5 tons per square foot. Copyright 2018 Geigle Safety Group, Inc. Page 9 of 22

16 7. Which of the following soil types is least stable? a. Class A b. Class B c. Class C d. Class D Visual Tests Visual testing involves looking at the soil and the area around the excavation site for signs of instability. The competent person might do visual tests such as the following: Observe the soil as it is excavated. Soil that remains in large clumps when excavated may be cohesive. Soil that breaks up easily is granular. Examine the particle sizes of excavated soil to determine how they hold together. Look for cracks or fissures in the faces of the excavation. Look for layers of different soil types and the angle of the layers in the face of the excavation that may indicate instability. Look for water seeping from the sides of the excavation. Look for signs of previously disturbed soil from other construction or excavation work. Consider vibration from construction activity or highway traffic that may affect the stability of the excavation. 8. Which of the following visual tests indicate stability? a. Signs of previously disturbed soil b. Soil that forms large clumps c. Cracks or fissures d. Layers of different soil Manual Tests Manual testing involves evaluating a sample of soil from the excavation to determine qualities such as cohesiveness, granularity, and unconfined compressive strength. Soil can be tested Copyright 2018 Geigle Safety Group, Inc. Page 10 of 22

17 either on site or off site but should be tested as soon as possible to preserve its natural moisture. Manual Test Examples Plasticity test: This is sometimes called the "pencil test." Shape a sample of moist soil into a ball and try to roll it into threads about 1/8-inch in diameter. Cohesive soil will roll into 1/8-inch threads without crumbling. Dry strength test: Hold a dry soil sample in your hand. If the soil is dry and crumbles on its own or with moderate pressure into individual grains or fine powder, it s granular. If the soil breaks into clumps that are hard to break into smaller clumps, it may be clay combined with gravel, sand, or silt. Thumb penetration test: This test roughly estimates the unconfined compressive strength of a sample. Press your thumb into the soil sample. If the sample resists hard pressure it may be type A soil. If it s easy to penetrate, the sample may be type C. Pocket penetrometers: offer more accurate estimates of unconfined compressive strength. These instruments estimate the unconfined compressive strength of saturated cohesive soils. When pushed into the sample, an indicator sleeve displays an estimate in tons per square foot or kilograms per square centimeter. 9. Which of the following manual test results indicates Class C soil? a. The soil sample is hard to break into smaller clumps b. The soil sample does not crumble using the plasticity test c. The thumb easily penetrates the soil sample d. The pocket penetrometer over 1.5 tons per square foot Competent Person A designated competent person who has training in soil analysis, protective systems, and OSHA's excavation requirements must be on site to classify the soil, select a protective system, oversee installation, and inspect the system after installation. If there are no existing hazards the competent person can leave the excavation site for a short time, but must be present when a protective system is moved. Soil conditions could change or new hazards may arise that require the competent person s judgment. Copyright 2018 Geigle Safety Group, Inc. Page 11 of 22

18 The competent person must be knowledgeable about the type of soil excavated and the protective system used and must inspect them daily for signs of instability, damage, or other hazards; The competent person must approve any changes. Inspections are also necessary after heavy rain or activities such as blasting that may increase the risk of cave-in. The competent person must have authority to immediately correct the hazards and to order employees to leave the excavation until the hazards have been corrected. An employee who is trained and can identify excavation hazards but doesn't have the authority to correct them is not a competent person. 10. An excavation competent person must. a. first obtain permission to make any changes b. have at least five years of excavation experience c. be a designated registered engineer d. have authority to immediately correct hazards Copyright 2018 Geigle Safety Group, Inc. Page 12 of 22

19 Module 2: Protection Systems Pre-Job Planning Pre-job planning is very important to prevent accidents when trenching. In other words, safety cannot be improvised as the work progresses. The following concerns must be addressed by a competent person: Evaluate soil conditions and select appropriate protective systems. Construct protective systems in accordance with the standard requirements. Contact utilities (gas, electric) to locate underground lines. Plan for traffic control, if necessary. Determine proximity to structures that could affect your choice of protective system. Test for low-oxygen, hazardous fumes and toxic gas, especially when gasoline enginedriven equipment is running, or the dirt has been contaminated by leaking lines or storage tanks. Provide safe access into and out of the excavation. Inspect the site daily at the start of each shift, following a rainstorm, or after any other hazard-increasing event. 1. What is always required because safety cannot be improvised as part of the excavation work process? a. Conduct pre-job planning b. Removal of all archaeological artifact c. Report all accidents to OSHA within 24 hours d. Continuous improvement processes Protective Systems All excavations are hazardous because they are inherently unstable. If they are restricted spaces, they present the additional risks of oxygen depletion, toxic fumes, and water accumulation. If you are not using protective systems or equipment while working in trenches Copyright 2018 Geigle Safety Group, Inc. Page 13 of 22

20 or excavations at your site, you are in danger of suffocating, inhaling toxic materials, fire, drowning, or being crushed by a cave-in. There are different types of protective systems. Sloping involves cutting back the trench wall at an angle inclined away from the excavation. Shoring requires installing aluminum hydraulic or other types of supports to prevent soil movement and cave-ins. Shielding protects workers by using trench boxes or other types of supports to prevent soil cave-ins. Designing a protective system can be complex because you must consider many factors: soil classification, depth of cut, water content of soil, changes due to weather or climate, surcharge loads (For example, spoil and other materials to be used in the trench) and other operations in the vicinity. 2. Each of the following is one of the three primary protective systems for excavations, EXCEPT. a. sloping b. shaking c. shoring d. shielding Other Safety Precautions The OSHA standard requires you to provide support systems such as shoring, bracing, or underpinning to ensure that adjacent structures such as buildings, walls, sidewalks, or pavements remain stable. The standard also prohibits excavation below the base or footing of any foundation or retaining wall unless: You provide a support system such as underpinning, The excavation is in stable rock, or A registered professional engineer determines the structure is far enough away from the excavation and the excavation will not pose a hazard to employees. Copyright 2018 Geigle Safety Group, Inc. Page 14 of 22

21 Excavations under sidewalks and pavements are prohibited unless you provide an appropriately designed support system or another effective means of support. There must not be any indications of a possible cave-in (while the trench is open) below the bottom of the support system. Also, you must coordinate the installation of support systems closely with the excavation work. Once the work is finished, you are required to backfill the excavation when you take apart the protective system. After the excavation is cleared, remove the protective system from the bottom up. Make sure you are careful! In the next section, you'll learn more about safely installing and removing protective systems. 3. What does OSHA require to make sure buildings, walls, sidewalks and pavements remain stable? a. Ensure the excavation is no closer than 50 feet to walls b. Provide warning notices to all building occupants c. Install guardrails around all excavations d. Provide shoring, bracing, or underpinning Installation and Removal of Protective Systems You must take the necessary steps to protect yourself and your employees when installing and removing a protective system. The OSHA standard requires you to take the following steps to protect your employees: Connect members of the support systems securely. Install support systems safely. Avoid overloading members of support systems. Install other structural members to carry loads imposed on the support system when you need to remove individual members temporarily. In addition, the standard permits excavation of two feet or less below the members of a support or shield system of a trench if the system is designed to resist the forces calculated for the full trench depth. Copyright 2018 Geigle Safety Group, Inc. Page 15 of 22

22 4. All of the following steps are required by OSHA when installing or removing a protective system, EXCEPT. a. avoid overloading members of support systems b. connect members of the support systems securely c. limit excavations below shield system to three feet d. install structural members to carry sufficient loads Appropriate Protective System Designs Designing a protective system can be complex. You must consider many factors, including: 1. soil classification 2. depth of cut 3. water content of soil 4. changes due to weather and climate 5. other operations in the vicinity Once you have selected an approach, however, the system must meet the required OSHA performance criteria. The OSHA standard describes methods and approaches for designing protective equipment. Let s discuss the different methods to designing protective equipment. Method 1: Sloping Slope the sides to an angle that isn't steeper than 1½:1. (34 degrees measured from the horizontal) For example, for every foot of depth, the trench must be excavated back 1½ feet. All simple slope excavations 20 feet or less deep should have a maximum allowable slope of 1½:1. These slopes must be excavated to form configurations similar to those for Type C soil. A slope of this gradation or less is safe for any type of soil. Copyright 2018 Geigle Safety Group, Inc. Page 16 of 22

23 5. To achieve a slope of 34 degrees, for every one foot in depth, excavate the sides back a. 1 foot b. 1½ feet c. 2 feet d. 2½ feet Method 2: Design Using Data Use tabulated data such as tables and charts approved by a registered professional engineer to design excavation. This data must be in writing and must include enough explanatory information, including the criteria for making a selection and the limits on the use of the data, for the user to make a selection. At least one copy of the data, including the identity of the registered professional engineer who approved it, must be kept at the worksite during the construction of the protective system. After the system is completed, the data can then be stored away from the jobsite. However, a copy must be provided upon request to the Assistant Secretary of Labor for OSHA. Method 3: Trench Box or Shield In this method, you would use a trench box or shield designed or approved by a registered professional engineer. Timber, aluminum, or other suitable material may also be used in the construction. OSHA standards permit the use of a trench shield if it provides the same level of protection as the appropriate shoring system. Employers can choose the most practical method for the particular circumstance, but that system must meet the required performance criteria. The standard doesn't require a protective system when an excavation is made entirely in stable rock or is less than five feet deep. However, in this case, a competent person must examine the ground and find no indication of a potential cave-in. Copyright 2018 Geigle Safety Group, Inc. Page 17 of 22

24 6. OSHA requires a protective system unless an excavation is. a. made entirely in stable rock or less than five feet deep b. made in Type A soil or under six feet in depth c. designed by a registered engineer or made in rocky soil d. approved by local utilities or made entirely in stable rock Benching There are two basic types of benching: simple and multiple. The type of soil determines the horizontal to vertical ratio of the benched side. As a general rule, the bottom vertical height of the trench must not exceed 4 feet. Subsequent benches may be up to a maximum of 5 feet vertical in Type A soil and 4 feet in Type B soil. All subsequent benches must be below the maximum slope allowed for that soil type. Also, in Type B soil, the trench excavation is permitted only in cohesive soil. Type C soil is not stable enough for benching as a protective system: use sloping instead. 7. Benching may be used as a protective system in which two soil types? a. Soil types A, B, or C b. Soil type A only c. Soil type B only d. Soils types A and B Shoring Types Shoring is the part of a support system for trench faces. It is used to prevent movement of soil, underground utilities, roadways and foundations. Shoring or shielding is used when the location or depth of the cut makes sloping back to the maximum allowable slope impractical. Shoring consists of posts, struts and sheeting. There are two types of shoring: timber and aluminum hydraulic. Copyright 2018 Geigle Safety Group, Inc. Page 18 of 22

25 Hydraulic Shoring Hydraulic shoring, a pre-fabricated strut and/or wale system made from aluminum or steel. Hydraulic shoring provides a critical safety advantage over timber shoring because workers do NOT have to enter the trench to install or remove hydraulic shoring. Other advantages to most hydraulic systems include: light enough to be installed by one worker gauge-regulated to ensure even distribution of pressure along the trench line can have their trench faces "pre-loaded" to use the soil s natural cohesion to prevent movement can be adapted easily to various trench depths and widths All shoring should be installed from the top down and removed from the bottom up. Hydraulic shoring should be checked at least once per shift for leaking hoses and/or cylinders, broken connections, cracked nipples, bent bases, and other damaged or defective parts. Pneumatic Shoring Pneumatic shoring works in a manner similar to hydraulic shoring. The primary difference is pneumatic shoring uses air pressure in place of hydraulic pressure. However, you need to have an air compressor on site when using pneumatic shoring. Air shoring involves using compressed air instead of hydraulic fluid to expand the trench jacks into position. Using the air type of system, pins are put in place to lock the jacks when a desired level of stability is achieved. To remove this type of trenching system, air is injected into the jacks to extend them. This allows the pin to be removed. These types of jacks are popular since they are cleaner than hydraulic jacks and there isn't a danger from the leakage of fluids or other lubrication. 8. Why does hydraulic shoring provide a critical safety advantage over timber shoring? a. Hydraulic shoring is less expensive to use b. Hydraulic shoring can be loaded with any kind of hydraulic fluid c. Workers do not have to enter the trench to install or remove shoring d. Timber shoring is heavier and less stable long-term Copyright 2018 Geigle Safety Group, Inc. Page 19 of 22

26 Other Protective Systems As mentioned earlier, when a trench is excavated, employees who work in the area must be protected from cave-ins. Therefore, the contractor should consider excavating a wider area than the necessary minimum. When this is done, it provides a more comfortable working environment for your employees in the trench. This extra working area may provide a way for workers to escape an unexpected crisis, such as falling objects or debris. Contractors should also reduce risk by limiting the number of workers in the trench at all times. The only workers allowed in the trench should be those who are absolutely needed to perform the task at hand. As the trench is backfilled, the braces and planks can be removed to be used at another site. If installed and removed correctly, vertical planks and trench braces may be used several times! Ingress and Egress Access to and exit from the trench require the following conditions: Trenches 4 ft. or more in depth should be provided with a fixed means of egress. Spacing between ladders or other means of egress must be such that a worker will not have to travel more than 25 ft. laterally to the nearest means of egress. Ladders must be secured and extend a minimum of 36 in (0.9 m) above the landing. Metal ladders should be used with caution, particularly when electric utilities are present. 9. When in a trench, workers should be no farther from a ladder than a. 15 feet b. 25 feet c. 30 feet d. 40 feet Additional Hazards and Protections In addition to cave-ins and related hazards, workers involved in excavation work are exposed to hazards involving falling loads and mobile equipment. To protect workers from these hazards, OSHA requires employers to take certain precautions. For example, employers must: Copyright 2018 Geigle Safety Group, Inc. Page 20 of 22

27 Protect workers from excavated or other materials or equipment that could pose a hazard by falling or rolling inside the excavation by placing and keeping such materials or equipment at least 2 feet (0.61 meters) from the edge and/or by using a retaining device to keep the materials or equipment from falling or rolling into the excavation. Provide a warning system (such as barricades, hand or mechanical signals, or stop logs) when mobile equipment is operated adjacent to an excavation, or when such equipment must approach the edge of an excavation, and the operator does not have a clear and direct view of the edge. Protect workers from loose rock or soil that could fall or roll from an excavation face by scaling to remove loose material, installing protective barricades at appropriate intervals, or using other equivalent forms of protection. Institute and enforce work rules prohibiting workers from working on faces of sloped or benched excavations at levels above other workers unless the workers at the lower levels are adequately protected from the hazards of falling, rolling, or sliding material or equipment. Institute and enforce work rules prohibiting workers from standing or working under loads being handled by lifting or digging equipment. Require workers to stand away from vehicles being loaded or unloaded to protect them from being struck by any spillage or falling materials. (Operators may remain inside the cab of a vehicle being loaded or unloaded if the vehicle is equipped, in accord with 29 CFR (b)(6), to provide adequate protection for the operator.) 10. Which of the following is NOT allowed when working in a trench? a. Provide a warning system when equipment is operating by the excavation b. Keep materials at least 2 feet from the edge of the excavation c. Workers may work under loads only if a spotter is close by d. Require workers to stand away from vehicles loading or unloading Copyright 2018 Geigle Safety Group, Inc. Page 21 of 22

28 Additional Resources Trenching and Excavation Safety, OSHA Excavations and Trenching, Oregon OSHA OSHA Technical Manual - Excavations, OSHA Safety Manual for Excavation, Ohio BWC Copyright 2018 Geigle Safety Group, Inc. Page 22 of 22