157 Excavation Safety: Basic

Glossary

This glossary includes terms associated with OSHA's Recommended Practices for Safety and Health Programs.

A

• Accepted engineering practices means those requirements which are compatible with standards of practice required by a registered professional engineer.
• Air Monitoring. The process of sampling the air within a trench or excavation to detect hazardous atmospheres, such as low oxygen levels, toxic gases, or combustible vapors. OSHA requires air monitoring in trenches deeper than 4 feet if there is a risk of hazardous atmosphere exposure.
• Aluminum Hydraulic Shoring means a pre-engineered shoring system comprised of aluminum hydraulic cylinders (crossbraces) used in conjunction with vertical rails (uprights) or horizontal rails (wales). Such system is designed specifically to support the sidewalls of an excavation and prevent cave-ins.

B

• Backhoe. A versatile piece of heavy equipment with a bucket attached to a long arm, commonly used for digging trenches, lifting materials, and moving soil. Backhoes are often used in excavation work because they can perform precise digging and maneuver in relatively small spaces.
• Bank. The material or ground adjacent to an excavation. Maintaining a stable bank is essential, as instability or erosion of the bank can lead to soil slipping or collapsing into the trench, posing risks to workers below.
• Bell-bottom pier hole means a type of shaft or footing excavation, the bottom of which is made larger than the cross section above to form a belled shape.
• Bench Excavation. An excavation method where horizontal steps or levels (benches) are cut into the trench walls. This technique reduces vertical pressure on trench walls, making it a safer method for excavations in cohesive soils. Bench excavation is often used in wide, deep excavations.
• Benching. A trench protection technique involving cutting the sides of a trench into a series of horizontal steps or benches, which reduce the vertical pressure on each level. This method is most effective in cohesive soils, such as clay, where each bench acts as a level of support for the one above it. Benching is not permitted for Type C soils, as they are too unstable. Bench height and width are determined by OSHA guidelines and the soil classification.
• Bucket. The scooping attachment on digging equipment, such as an excavator or backhoe, used to remove soil and material from an excavation site. Buckets come in various sizes and designs, tailored to specific types of soil and tasks (e.g., trenching, loading, or rock excavation).

C

• Cave-in. A dangerous situation where trench walls suddenly collapse, sending soil or rock into the excavation. This can occur when trench walls are inadequately supported, making it a leading cause of fatalities in excavation work. Cave-ins can bury workers under several tons of soil in seconds, leaving little time for escape. OSHA mandates protective measures in trenches deeper than 5 feet to prevent cave-ins.
• Competent Person. An individual assigned by an employer to oversee safety on an excavation site. This person must be knowledgeable about trenching hazards, soil classifications, and protective systems, and has the authority to make changes as needed. A competent person inspects the trench daily, especially after events like rain or heavy equipment activity, which may destabilize trench walls. OSHA requires a competent person to monitor excavations to ensure compliance and address hazards.
• Compactor. A machine used to compress or compact soil in an excavation or trench, making it more stable. Compactors are often used in backfill operations to reduce soil movement and prevent future settlement, which can destabilize structures.
• Crawler Excavator. A type of excavator with tracks instead of wheels, providing increased stability on uneven or soft surfaces. Crawler excavators are commonly used in trenching operations where maneuverability and stability are essential for safe digging.
• Cross Bracing. Structural support used within shoring systems to increase stability by holding opposing trench walls in place. Cross braces can be installed horizontally or at an angle, and they help prevent soil movement within the trench.

D

• Degradation. The process by which soil strength is reduced, often due to factors like moisture, exposure to weather conditions, or vibrations from nearby equipment. Degradation increases the likelihood of trench collapse and requires additional protective measures.
• Dewatering Pump. A device used to remove water that accumulates in an excavation site, helping maintain dry and stable conditions. Dewatering pumps are essential in trenching and excavation operations where water intrusion could weaken soil and lead to cave-ins.
• Dragline Excavator. A type of heavy equipment with a large bucket suspended from a boom, used for removing soil from large, deep excavations. Dragline excavators are effective in moving soil over long distances and are often used in large-scale excavation projects.

E

• Encroachment. The presence of heavy equipment, materials, or traffic near the edge of an excavation. Encroachment can destabilize the trench walls by adding pressure to the edges, increasing the risk of collapse. OSHA recommends maintaining a "setback distance" for heavy equipment near trench edges.
• Excavation. Any human-made cut, cavity, trench, or depression formed by removing soil, rock, or other earth materials. Excavations can range from shallow ditches to deep trenches used for utility lines or foundations. OSHA enforces specific safety regulations for excavation work due to the high risk of cave-ins, hazardous atmospheres, and other risks.

F

• Face of the Excavation. The vertical or inclined surface on the side of an excavation. Managing the face of the excavation is crucial for stability, as improperly managed faces can lead to soil movement or collapse, endangering workers inside the trench.
• Faces or sides means the vertical or inclined earth surfaces formed as a result of excavation work.
• Failure means the breakage, displacement, or permanent deformation of a structural member or connection so as to reduce its structural integrity and its supportive capabilities.
• Fall Protection. Safety measures designed to prevent falls into an excavation, which may include guardrails, barriers, and personal fall arrest systems. When trench depths exceed 6 feet or more, OSHA requires fall protection measures to prevent accidents from above-ground personnel, equipment, or materials inadvertently falling into the trench.

G

• Grade. The slope or level of the ground surrounding an excavation. Maintaining an even grade is essential to prevent water runoff into the trench, which could weaken trench walls and increase the risk of cave-ins.

H

• Hazard Analysis. A detailed assessment conducted to identify potential risks associated with trenching and excavation activities. Hazard analyses help in planning protective measures, such as choosing appropriate shoring, sloping, or shielding systems.
• Hazardous Atmosphere. A dangerous air environment in a trench, which may contain toxic gases, flammable vapors, or oxygen-deficient air. Common sources include decaying materials, natural gases, or nearby industrial activities. OSHA requires atmospheric testing before entry into trenches deeper than 4 feet where these hazards may exist, and adequate ventilation or other measures if unsafe conditions are detected.
• Hydraulic Shoring. A protective system that uses hydraulic pistons and panels to support trench walls. Hydraulic shoring can be quickly adjusted, making it a popular choice for trenches with varying soil stability. The system is designed to prevent cave-ins by applying pressure against trench walls.

I

• Ingress and Egress. Safe entry and exit from trenches and excavations, typically achieved by ladders, steps, ramps, or other devices. OSHA mandates that ladders or other access points be located within 25 feet of workers in trenches that are 4 feet deep or more. Proper ingress and egress prevent falls and help workers exit quickly in case of emergency.
• Inspections. Regular checks conducted by a competent person to ensure trench safety, identify hazards, and confirm the stability of protective systems. Inspections are required at least once daily and must be performed more frequently after rain, vibrations, or other conditions that could affect trench stability.

J

K

• Kickout. The displacement or ejection of shoring or shielding systems from a trench wall, typically caused by lateral pressures from the soil. A kickout can lead to immediate collapse and is a serious hazard for workers within the trench.

L

• Ladder. An essential piece of equipment in trenching, ladders provide safe entry and exit for workers. OSHA requires ladders within 25 feet of all workers in trenches deeper than 4 feet, allowing for a quick escape in emergencies.
• Ladder Access. The provision of ladders within a trench or excavation for safe entry and exit. OSHA requires that ladders be located within 25 feet of all workers in trenches deeper than 4 feet to ensure quick and easy escape in emergencies.
• Laser Level. A precision tool used to ensure that trench bottoms and pipe installations are level, which is essential for accurate drainage and structural stability. Laser levels are frequently used in excavation to maintain accuracy and alignment over long distances.

M

N

O

• Overburden. The soil or material that lies above the level of the excavation, which can exert additional pressure on trench walls, increasing the risk of collapse. OSHA recommends storing overburden materials at least 2 feet from the trench edge to avoid added stress on trench walls.

P

• Pile Driving. The use of heavy equipment to drive piles into the ground near an excavation site. This process creates vibrations that can destabilize trench walls and increase the risk of cave-ins. OSHA requires additional precautions when pile driving is performed near trenches.
• Pneumatic Shoring. A trench support system that uses air pressure to stabilize trench walls. Pneumatic shoring systems are highly effective for quick adjustments and are commonly used in trenches with rapidly changing soil stability.
• Protective System. Methods and equipment designed to prevent trench walls from collapsing and to protect workers from soil, rocks, or materials falling into the excavation. Protective systems include sloping, shoring, benching, and shielding. The choice of protective system depends on factors like soil type, trench depth, and nearby vibrations.

Q

• Qualified Person. An individual with in-depth knowledge and experience who can assess conditions and hazards related to a specific type of work, such as trenching. This person may design or approve protective systems for deep excavations and is often involved in creating safety protocols tailored to specific excavation projects. OSHA requires qualified persons for certain tasks, such as designing trench protections deeper than 20 feet.
• Quick Coupler. A hydraulic device used on excavators to quickly switch between attachments, such as buckets or hammers, without the need for manual adjustments. Quick couplers increase efficiency and flexibility in trenching operations, allowing for quick changes between digging, lifting, or breaking tasks.

R

• Rammer. A compacting tool used to compress soil and backfill in a trench, creating a stable foundation for pipes or structures. Rammers are typically handheld and use high-impact forces to pack down loose soil, reducing the risk of future settlement.
• Ramp. An inclined surface used to allow access into or out of an excavation, often as an alternative to ladders. Ramps must be stable, constructed to support the weight of both workers and equipment, and designed to prevent slipping.
• Registered Professional Engineer means 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.

S

• Shear Wall. A vertical section of trench wall that has not been sloped, benched, or supported. Shear walls present significant risks if not stabilized and are generally only allowed in stable soil types.
• Sheepsfoot Roller. A type of compactor with raised, knob-like feet on its drum, designed for compacting cohesive soils. Sheepsfoot rollers are commonly used in trenching to compress backfill materials, preventing soil settling and providing a stable foundation.
• Sheeting means the members of a shoring system that retain the earth in position and in turn are supported by other members of the shoring system.
• Shielding. A protective measure using trench boxes or other structures to protect workers within the trench. Shields, unlike shoring, do not prevent a cave-in but create a safe zone if one occurs. Trench boxes are most common and should be installed properly to provide maximum safety. OSHA requires shielding systems in unstable soils or deep trenches unless another protective method is in place.
• Shoring. A support system that stabilizes trench walls, typically made from hydraulic, mechanical, or timber structures to prevent soil movement and cave-ins. Shoring systems are crucial in trenches with unstable or weak soil types, as they create a supportive structure within the trench walls. OSHA defines specific requirements for shoring based on soil stability and trench dimensions.
• Shoring Box. Also known as a trench box, a shoring box is a protective device placed within a trench to prevent soil from caving in on workers. Shoring boxes are made of steel or aluminum and provide a safe zone inside the trench by holding back soil pressure.
• Sloping. A method of excavation where trench walls are cut back at an angle based on soil classification, which lessens the risk of wall collapse. Sloping creates a gradual incline, redistributing weight to minimize cave-ins, and is often used with stable soil types. OSHA specifies angle ratios for different soil types; for example, Type C soils require a 1.5:1 ratio (1.5 feet horizontal to 1 foot vertical).
• Soil Classification. The process of categorizing soil into Type A, Type B, or Type C, according to OSHA standards, which helps determine the level of protective measures required. Type A is the most stable (e.g., clay), Type B is moderately stable (e.g., silt), and Type C is the least stable (e.g., sand or gravel). Soil testing by a competent person helps guide decisions on sloping, benching, and shoring.
• Spoil Pile. The pile of excavated soil and material located near a trench or excavation. OSHA requires that spoil piles be kept at least 2 feet from the edge of the trench to prevent material from falling back into the excavation, which could cause injuries or destabilize the trench walls.
• Stable rock means natural solid mineral material that can be excavated with vertical sides and will remain intact while exposed. Unstable rock is considered to be stable when the rock material on the side or sides of the excavation is secured against caving-in or movement by rock bolts or by another protective system that has been designed by a registered professional engineer.
• Structural ramp means a ramp built of steel or wood, usually used for vehicle access. Ramps made of soil or rock are not considered structural ramps.
• Support system means a structure such as underpinning, bracing, or shoring, which provides support to an adjacent structure, underground installation, or the sides of an excavation.
• Surveying Equipment. Tools such as GPS units, laser levels, and total stations used to measure and map excavation sites accurately. Surveying equipment ensures that trenches are excavated at the correct depth, alignment, and grade, which is crucial for structural integrity and drainage.

T

• Tabulated data means tables and charts approved by a registered professional engineer and used to design and construct a protective system.
• Toe of the Slope. The bottom of an inclined trench wall where the sloped or benched section meets the trench floor. Properly managing the toe of the slope is crucial to prevent soil from sliding into the trench and to maintain stability.
• Trench (Trench excavation) means a narrow excavation (in relation to its length) made below the surface of the ground. In general, the depth is greater than the width, but the width of a trench (measured at the bottom) is not greater than 15 feet (4.6 m). If forms or other structures are installed or constructed in an excavation so as to reduce the dimension measured from the forms or structure to the side of the excavation to 15 feet (4.6 m) or less (measured at the bottom of the excavation), the excavation is also considered to be a trench.
• Trench Box. A protective shield that prevents cave-ins by supporting trench walls. Made of steel or aluminum, trench boxes are used in trenches with unstable soil and are essential for protecting workers from cave-ins. Trench boxes can be adjusted to different depths and are moved as excavation progresses.
• Trencher. A machine specifically designed for digging narrow, straight trenches, often used for laying utilities or pipelines. Trenchers come in various types, including chain trenchers, which use a chain to dig through soil, and micro-trenchers, which create small, shallow trenches for fiber optic cables.
• Trench Shield. A heavy-duty protective structure, often made of steel or aluminum, designed to prevent soil from caving into a trench, thus protecting workers inside. Unlike shoring, which supports the walls of the trench to prevent movement, a trench shield acts as a shield around workers, creating a safe zone in the event of a collapse. Trench shields are generally placed inside trenches and moved along as work progresses. They are commonly used in deeper or unstable soils and are required by OSHA when other trench protection methods are insufficient. Trench shields are also known as "trench boxes" and are available in various sizes to accommodate different trench dimensions.
• Type A Soil. The most cohesive and stable soil type, which includes undisturbed clay and silty clay. Type A soils can support steeper trench walls than less stable types, requiring less protective support. However, even Type A soil can lose stability under vibrations, moisture, or weather changes.
• Type B Soil. A moderately cohesive soil that is less stable than Type A. This includes silt, silt loam, and previously disturbed soils. Trenching in Type B soils requires more conservative angles for sloping and additional protective measures like benching or shoring, as it is more prone to collapse.
• Type C Soil. The least stable soil classification, which includes sand, gravel, and other loose or granular materials. Type C soil requires the most stringent protective systems and cannot safely support sloping alone. Because of its high risk of collapse, trenches in Type C soils need protective measures like shoring and shielding.

U

• Undercutting. The practice of excavating soil or material from beneath a structure or bank, which can destabilize the structure and cause collapse. OSHA discourages undercutting in excavation sites due to the high risk of destabilizing surrounding soil and structures.
• Undermining. A condition where soil erosion or displacement occurs below the surface of the trench, which weakens the trench walls and increases the risk of collapse. Factors like nearby water sources, improper excavation methods, or vibrations from machinery can cause undermining, making regular inspections vital.
• Uprights means the vertical members of a trench shoring system placed in contact with the earth and usually positioned so that individual members do not contact each other. Uprights placed so that individual members are closely spaced, in contact with or interconnected to each other, are often called "sheeting".
• Utility Locating. The practice of identifying and marking underground utility lines, including gas, water, electricity, and telecommunications, before excavation work begins. Utility locating helps avoid accidental strikes on utility lines, which can result in injuries, equipment damage, or environmental hazards. OSHA requires that utilities be located before starting excavation to ensure a safe work environment.

V

• Vibration Monitoring. The process of observing and controlling vibrations from machinery or nearby traffic to prevent destabilization of trench walls. Vibrations can weaken trench stability, and OSHA requires special precautions in areas with high vibration activity.
• Vibratory Plate Compactor. A machine with a flat metal plate that vibrates to compact loose soil or gravel, often used in backfilling operations to stabilize soil layers. Vibratory compactors are crucial for creating a firm base in trenches, reducing soil settlement and supporting the trench’s structural integrity.

W

• Wales means horizontal members of a shoring system placed parallel to the excavation face whose sides bear against the vertical members of the shoring system or earth.
• Walkway or Bridge. A structure that spans over an excavation or trench, allowing workers to cross safely without entering the trench. Walkways and bridges must have guardrails if the trench depth or width poses a fall hazard. These structures prevent accidental falls into the excavation and ensure a continuous path over the work site.
• Water Accumulation. The collection of water in a trench or excavation site, which can destabilize soil and increase the likelihood of a cave-in. Water accumulation may occur from rain, groundwater, or leaks, and OSHA requires dewatering solutions, such as pumps or drainage, to reduce risks and maintain trench stability.
• Weather-Related Hazards. Environmental conditions such as rain, snow, freezing, or high heat that can weaken trench walls, reduce soil stability, and create slip hazards. OSHA requires additional inspections and safety measures to manage weather-related hazards in trenching work.
• Wheel Loader. A heavy equipment machine with a large bucket at the front used to load soil, gravel, or other materials into trucks or onto spoil piles. Wheel loaders are often used on excavation sites to move large volumes of material quickly, facilitating efficient material handling.

X

• X-Ray Fluorescence (XRF) Testing. A non-destructive testing method used to detect and analyze elements in soil or material samples. XRF can help identify contaminants and assess soil composition, which is critical in understanding soil behavior for trenching and excavation safety.

Y

• Yield Point. The stress level at which soil or a trench wall begins to deform or collapse. Understanding the yield point of the soil helps in determining the right protective systems, as materials beyond this point cannot maintain their shape under pressure.

Z

• Zero Energy State. A condition where all energy sources, such as utilities, vibrations, and machinery, are secured and de-energized before excavation. This state minimizes the risk of accidental activation of equipment or disturbances that could weaken trench walls. Ensuring a zero-energy state protects workers from sudden hazards, particularly when underground utility lines or machinery vibrations are nearby.
• Zone of Influence. The area surrounding an excavation that may be affected by soil movement or load pressures. Heavy equipment, material storage, or vehicle movement within the zone of influence can increase the likelihood of trench wall collapse. OSHA recommends keeping heavy loads away from the trench edge to minimize risk within the zone of influence.