Excavation Safety

Excavation Safety

Excavation Safety • Trenching and excavation procedures are among the most hazardous of all construction activities. • Tens of thousands of people work in trenches and excavations every day • This course is designed to equip you with the knowledge you need to reduce your likelihood of injury while working in or around trenching and excavation work sites. Excavation Safety

Excavation Safety • AECOM Excavation Policies are slightly different for each of the following regions. • North America • UK, Ireland, Europe, and Middle East • Asia Pacific Excavation Safety

Excavation Safety • By the end of this course, you will be able to: • Recognize trenching and excavation hazards. • Know the AECOM safety requirements for trenching and excavation activities. Excavation Safety

Excavation Safety • Let’s begin by examining trenching and excavation hazards. • Recognize trenching and excavation hazards. • Know the AECOM safety requirements for trenching and excavation activities. Excavation Safety

Trenching and Excavation Hazards • What is a trench: A trench is a narrow excavation made below the surface of the ground. In general, the depth of a trench is greater than its width, and the width (measured at the bottom) is not greater than 15 feet (4.6 meters). • What is an excavation: An excavation is any man-made cut, cavity, trench, or depression in the earth. Excavation Safety

Trenching and Excavation Hazards • Studies done by NIOSH show that, between 1992 and 2006, about 1,000 lost time injuries occurred annually in the US as a result of excavation and trench cave-ins. Of these, an average of 47 per year are known to result in death. Some experts believe this number may be well over 100 per year. Excavation Safety

Trenching and Excavation Hazards • Cyprus: Worker Rescued from Unstable Excavation – An East European worker was safely rescued from a 4 meter (13 foot) deep unstable excavation in the Strovolos district of Nicosia where sewage pipe work had been undertaken. 26 November 2009 • United States: Worker Dies in Trench Collapse – A 38-year old male construction laborer died when the unprotected 8 foot (2.4 meter) high walls of the trench he was working in collapsed. 3 November 2003 • New Zealand: Worker Dies in Excavation Collapse – A 34-year old worker died after becoming trapped in a 13 foot (4 meter) deep excavation at a landfill site. 12 December 2009 Excavation Safety

Trenching and Excavation Hazards • A person partially or fully buried in a trench collapse is likely to suffer: • Fractures • Bruises, contusions, and abrasions • Sprains and strains • Cuts and lacerations • Concussions • Amputations • Asphyxiation • Death Excavation Safety

Trenching and Excavation Hazards Delete slide? • This video demonstrates how quickly an excavation collapse an happen. Excavation Safety

Trenching and Excavation Hazards • Why do serious injuries and fatalities continue to occur? • The items below are examples of things that contribute to casual behaviors around excavation sites. • Lack of training. • Perception of the safety costs associated with the excavation as excessive and unnecessary. • Insufficient enforcement of safety requirements by management. • Perception of personal immunity. (It will not happen to me! I can outrun an excavation collapse! • A casual attitude towards excavation safety will increase your likelihood of being injured. Excavation Safety

Trenching and Excavation Hazards • Why are excavation and trenches potentially hazardous. • Soil is extremely heavy. A cubic yard of soil, less than the size of an average office desk, may weigh more than 2,700 pounds (1,227.3 kilograms), the equivalent of a midsize car. • Many people think they can push their way out of a collapsed trench or excavation, but even a world class weightlifter can bench press only about 500 pounds (227kilograms). Excavation Safety

Trenching and Excavation Hazards • The most common hazards at any excavation or trench site are below. • Falls: Someone could accidentally fall into the excavation. • Cave-ins: There is no longer material available to support the walls of the excavation. Pressure from the surrounding soil could cause the walls to collapse. • Falling Vehicles: A vehicle may fall into the excavation if the operator does not have a clear and direct view of the excavation’s edges. • Vehicle Pressure: Vehicles add additional pressures to the already weakened soil. • Falling Loads: Falling loads present a hazard because someone may be working underneath. The vehicle operator may not see them and unload on top of them. • Hazardous Atmospheres: An excavation may be considered a confined space. Appropriate evaluation and controls must be taken to avoid exposure to contamination. • Loose Rock or Soil: Loose rock or soil may fall or roll from an excavation face. This may injure workers in the excavation. • Water: Water increases the possibility of cave-ins. The increased water pressure exerted on the soil can be a factor in causing the wall to collapse. • Adjacent Structures: Structures rely on a sold foundation to evenly distribute the weight. When the foundation is undermined, the excavation or structure may collapse or shift. • Underground Installations: Water, sewer, telephone, fuel, and electric lines. . Excavation Safety

Excavation Safety • The remainder of this course will focus on the steps you can take to reduce your chances of being injured on a trenching or excavation site. • Recognize trenching and excavation hazards. • Know the AECOM safety requirements for trenching and excavation activities. Excavation Safety

Excavation Requirements • AECOM Health and Safety Policies outline nine requirements for excavation work • An excavation competent person • Preliminary planning • Access and egress • Soil classification • Protection systems • Hazardous atmospheres • Prevention of water accumulation • Permit authorizations and inspections • Training and briefings • Refer to the Safety, Health, and Environment AECOM Ecosystem page for more information. Excavation Safety

Excavation Requirements – Competent Person • Where potential employee exposure to hazards associated with the excavation can reasonably be anticipated, an excavation competent person must be on site. The excavation competent person: • Has formal documentation of training as an excavation competent person. • Must be physically located at the excavation site at all times while work is in progress. • Is responsible for conducting daily inspections of excavations, adjacent areas, and protective systems prior to each shift. • Is responsible for inspection after every rainstorm or other potentially hazard-producing event. • Must have knowledge of soils and soil classification. • Understands design and use of protective systems. • Understands the requirements of the applicable regulations. • Has authority to stop work and take corrective actions when conditions change. • Has the ability to recognize and test hazardous atmospheres. • If AECOM hires a subcontractor to perform excavation or trenching activities, the subcontractor will be required to assign an excavation competent person to the project. Documentation of this person’s qualifications will be maintained in the project safety file. Excavation Safety

Excavation Requirements – Preliminary Planning • Prior to any excavation activities, AECOM must evaluate the following: • The presence of underground or overhead utilities. • Adjacent structures or retaining walls. • Placement of spoil or soil piles away from future excavation work. • Routes of heavy equipment and vehicular traffic. • Development of emergency procedures. Excavation Safety

Excavation Requirements – Soil Classification • To understand soil pressures in excavations, look at this example. Think of the ground as many 1 foot (.3 meters) square blocks. Remember, a cubic foot of soil weights about 100 pounds (45 kilograms Excavation Safety

Excavation Requirements – Soil Classification • A block 5 feet (1.5 meters) deep supports its own weight and the weight of the four blocks above it. So there is a 500 pound (227 kilograms) force exerted vertically on whatever lies below. Excavation Safety

Excavation Requirements – Soil Classification • Additionally, there is a horizontal force in all outward directions. The outward force is equal to one-half of the vertical force Excavation Safety

Excavation Requirements – Soil Classification • In the earth, the columns press against each other to maintain equilibrium Excavation Safety

Excavation Requirements – Soil Classification • When a trench is excavated the equilibrium is broken. One of the blocks may no longer be able to support its weight and the blocks above it, causing a trench failure. Excavation Safety

Excavation Requirements – Soil Classification • These pictures can show some common causes of excavation and trench failures. • Tension Crack: Tension cracks form at a horizontal distance of 0.5 to 0.75 times the depth of the trench • Substance and Bulging: An unsupported excavation can create an unbalanced stress in the soil which causes subsidence at the surface and bulging of the vertical face of the trench. Excavation Safety

Excavation Requirements – Soil Classification • These picture can show some common causes of excavation and trench failures. • Heaving or Squeezing: 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. • Sliding or Sluffing: Sliding, also called sluffing, is a result of tension cracks. Excavation Safety

Excavation Requirements – Soil Classification • These picture can show some common causes of excavation and trench failures. • Boiling: An upward flow of water into the bottom of the cut is evidence of boiling, which is often caused by a high water table. • Toppling: Toppling is also caused by tension cracks. It occurs when the trench’s vertical face shears along the tension crack line and topples into the excavation Excavation Safety

Excavation Requirements – Soil Classification • There are four classifications of rock and soil. The classification you are working with will dictate the type of protective system you will need. • When sloping, benching, or installed protective systems are used, soil classification of each rock and soil deposit must be completed by a competent person. Excavation Safety

Excavation Requirements – Soil Classification • Stable Rock: 1) Natural solid mineral material. 2) Vertical sides will remain intact while exposed. • Type A: Cohesive soils with an unconfined compressive strength of 1.5 tons per square foot (tsf) (144 kPa) or greater. Examples: clay, silty clay, sandy clay, clay loam, cemented soils, silty clay loam-in some cases, and sandy loam – in some classes. No soil is type A if the soil: 1) is fissured; 2) has been previously disturbed; 3) is subject to vibration from heavy traffic, pile driving, etc.; 4) is subject to other factors that would require it to be classified as a less stable material • Type B: 1) Cohesive soil with an unconfined compressive strength greater than 0.5 tsf (48 kPa) but less than 1.5 tsf (144 kPa). 2) Granular cohesionless soils including angular gravel, silt, silt loam, sandy loam, and in some cases, silty clay loam and sandy clay loam. 3) Previously disturbed soils except those which would otherwise be classified as Type C. 4) Dry rock that is not stable. 5) Soil that meets the unconfined compressive strength or cementation requirements for Type A but is fissured or subject to vibration. Excavation Safety

Excavation Requirements – Soil Classification Type C: 1) Cohesive soil with an unconfined compressive strength of 0.5 tsf (48 kPa) or less. 2) Granular soils including gravel, sand, and loamy sand. 3) Submerged soil or soil from which water is freely seeping. 4) Submerged rock that is not stable. Excavation Safety

Excavation Requirements – Soil Classification • Each layer may be classified individually. If not classified individually, the soil must be classified on the basis of the soil classification of the weakest soil layer. • Base the classification of the results of at least one visual and one manual analysis. See the Safety, Health, and Environment AECOM Ecosystem page for more information. • If the soil types are unknown, you must assume the soil is Type C. Excavation Safety

Excavation Requirements – Soil Classification • What is the order of these soil types in order of strength. • Sand • Stable Rock • Clay • Silt Excavation Safety

Excavation Requirements – Protective Systems • Cave-ins are the most dangerous excavation hazard. Anyone working in an unprotected excavation or trench can potentially be engulfed. For this reason, the best protection from a cave-in is not to enter the excavation at all. There is often a way to get what you need without entering the excavation. For example • Get soil samples from the excavation using a backhoe. • Build piping systems above ground and lower then into the excavation. • Lower a video camera to inspect the excavation or boring. Excavation Safety

Excavation Requirements – Protective Systems • AECOM requires that excavations over 4 feet (1.2 meters) deep offer protection from cave-in by • Sloping • Benching • Shoring • Shielding • Excavations greater than 20 feet (6 meters) must be designed and stamped by a registered Professional Engineer. Excavation Safety

Excavation Requirements – Protective Systems • Sloping prevents cave-ins by providing inclined walls away from the excavation. The degree of the slope is determine by the type of soil. These simple slopes can only be used in excavations 20 feet (6.1 meters) deep or less. Excavation Safety

Excavation Requirements – Protective Systems • Benching is achieved when the sides of the excavation form a series of horizontal levels or steps. Excavation Safety

Excavation Requirements – Protective Systems • Benching: • As a general rule, the bottom vertical height of the trench must not exceed 4 feet (1.2 meters) for the first bench. • Subsequent benches may be up to a maximum of 5 feet (1.5 meters) vertical in Type A soil and 4 feet (1.2 meters) in Type B soil to a total depth of 20 feet (6 meters). • Subsequent benches must be below the maximum allowable slope for that soil type. • For Type B soil, benching the excavation is permitted in cohesive soil only. Excavation Safety

Excavation Requirements – Protective Systems • Shoring is the use of a metal, hydraulic, mechanical, or timber structure to support he sides of the excavation. • Prevents the movement of soil, underground utilities, roadways, and foundations. • Used when the location or depth of the cut makes sloping back to the maximum allowable slope impractical. • Consists of posts, wales, struts, and sheeting. • All shoring should be installed from the top down and removed from the bottom up. Excavation Safety

Excavation Requirements – Protective Systems • There are two basic types of shoring. • Timber Shoring: 1) Can take two or more workers to install. 2) Workers must enter the trench for installation and removal. 3) Knots and other imperfections in the wood can lead to failure. 4) Cutting word to appropriate sizes can be costly and difficult. • Hydraulic Shoring: 1) Light enough to be installed by one worker. 2) Workers do not have to enter the excavation for installation and removal. 3) Easily adaptable to various depths and widths. 4) Gauge-regulated to ensure even distribution of pressure along the trench line. 5) Today, the trend is toward using hydraulic shoring because of its safety advantages over timber shoring. Excavation Safety

Excavation Requirements – Protective Systems • A shield or trench box protects the workers within the structure by shielding them from forces imposed on it by a cave-in. A shield or trench box: • Can be permanent or temporary. • Does not support excavation walls like shoring. • The area between the trench box and the excavation face should be as small as possible. • The area between the trench box and excavation face should be backfilled to prevent lateral movement of the box. • Shield loads must not exceed those which it was designed to withstand. Excavation Safety

Excavation Requirements – Protective Systems • Let’s review. Match the protective system to the matching definition. Sloping Benching Shoring Shielding or trench box 1. Uses a metal, hydraulic, mechanical or timber structure to support the sides of the excavation. 2. Protects the workers within the structure by shielding them from forces imposed on it by a cave-in. 3. Achieved when the sides of the excavation for a series of horizontal levels. 4. Prevents cave-ins by providing inclined walls away from the excavation. Excavation Safety

Excavation Requirements – Protective Systems • Protective systems must have the capacity to resist all loads that are intended or could reasonably be expected to be applied or transmitted to the system. • 1) Soil classification • 2) Depth of cut • 3) Water content of soil • 4) Underground utilities • 5) Other operations in the area • 6) Type of work to be done in the trench • Protective systems for excavations or trenches deeper than 20 feet (6 meters) must be designed and stamped by a registered Professional Engineer. Excavation Safety

Excavation Requirements – Protective Systems • Vehicle Traffic – Warning Systems • Mobile equipment may fall into the excavation if the operator does not have a clear view of the edge of the excavation area. A warning system must be in place to prevent an incident • Hand signals or mechanical signals • Barricades • Stop logs Excavation Safety

Excavation Requirements – Protective Systems • Falling Loads • Workers should never stand under loads handled by lifting or digging equipment. Don appropriate personal protective equipment when working in close proximity to heavy equipment (hard hat, safety glasses, steel-toed boots, traffic vest, hearing protection). Excavation Safety

Excavation Requirements – Protective Systems • Adjacent Structures • A support system must be used if there is a structure adjacent to the excavation. Support systems include: • Shoring • Bracing • Underpinning Excavation Safety

Excavation Requirements – Protective Systems • Loose rock or soil may fall or roll into the excavation. Here are things you can do for protection from falling rock or soil. • Loose material should be removed from the excavation wall. • Excavated material or other equipment should be kept away from the edge of the excavation. Local regulations usually require guardrails, barricades, or fall arrest systems when equipment or personnel are within a certain distance of the excavation • The excavation face should have a protective barricade to stop and contain falling material. • Retaining devices should be used to prevent excavated material or equipment from falling or rolling into the excavation Excavation Safety

Excavation Requirements – Protective Systems • Fall protection must be provided to prevent employees from falling into an excavation. • Many walkways located above lower levels must have guardrails (see your local regulations for details). • Temporary excavations must be backfilled upon completion. • Excavations must be covered or barricaded to prevent falls. Covers must be labeled and secured to prevent accidental removal. Excavation Safety

Excavation Requirements – Protective Systems • Vehicle crossings, walkways, and bridges should not be made unless absolute necessary. • If such access-ways are required, they must be designed by and installed under the supervision of a registered Professional Engineer. Excavation Safety

Excavation Requirements – Hazardous Atmospheres • Any excavation greater than 4 feet (1.2 meters) deep with a potential for a hazardous atmosphere should be tested and monitored. This includes excavations in which are: • Oxygen concentrations less than 19.5%. • Flammable gases greater than 10% of the lower flammable limit. • Toxic chemicals greater than a chemical's published exposure limit. Excavation Safety

Excavation Requirements – Hazardous Atmospheres • When required, air monitoring should be conducted at multiple vertical depths of the excavation to detect potentially stratified gas layers. Gases with heavy densities may accumulate at the bottom of a trench or excavation. • Air monitoring must be documented and maintained in the project safety files. Project Safety File Excavation Safety

Excavation Requirements – Hazardous Atmospheres • If hazardous conditions are present, the following must be provided: • Respiratory protection • Ventilation • Emergency rescue teams and/or equipment • If the excavation qualifies as a confined space, a Confined Space Entry Permit may be required. Excavation Safety

Excavation Requirements – Access and Egress • AECOM requires ramps or ladders within 25 feet (7.5 meters) of the entrance for excavations deeper than 4 feet (1.2 meters). • This means that an employee should not have to travel more than 25 feet (7.5 meters) to the nearest access. • Ideally, ladders should be placed as close as possible to the employees working in the trench or excavation. Ladders must extent 3 feet (0.8 meters) above the excavation leading edge and it must be fixed to ensure stability. Excavation Safety

Excavation Safety