Instructor: George Bunker 970-632-4917

Course Duration: 3 Hours

 Definition:

• Trenching: A narrow excavation (depth > width) made below the surface of the ground.
• Excavation: Any man-made cut, cavity, trench, or depression in the earth’s surface formed by earth removal.

Common injuries and fatalities associated with trenching and excavation

Trenching and excavation work can be highly dangerous if proper safety measures aren't followed. Here are some common injuries and fatalities associated with trenching and excavation work:

1. Cave-Ins (Collapses)

• Most Common Cause of Fatalities:
  • Cave-ins occur when trench walls collapse, burying workers under soil. Soil can weigh as much as 3,000-4,000 pounds per cubic yard, making it nearly impossible for trapped workers to escape.
  • Injuries: Asphyxiation, crush injuries, fractures, and death.
  • Fatalities: Most fatalities result from suffocation or being crushed by the soil.

2. Falls

• Falling into Trenches:
  • Workers, equipment operators, or pedestrians can fall into unprotected trenches or excavations.
  • Injuries: Broken bones, head injuries, and lacerations.

3. Struck-by Incidents

• Falling Materials or Equipment:
  • Tools, materials, or heavy machinery can fall into trenches, striking workers.
  • Injuries: Head injuries, fractures, spinal injuries, and death.
• Mobile Equipment Strikes:
  • Workers in or near trenches may be struck by moving equipment, such as backhoes or trucks, due to limited visibility or improper communication.
  • Injuries: Crush injuries, amputations, or fatalities.

4. Hazardous Atmospheres

• Oxygen Deficiency:
  • Excavations may expose workers to hazardous atmospheres such as oxygen-deficient environments or the presence of toxic gases.
  • Injuries: Loss of consciousness, respiratory issues, suffocation, and fatalities.
• Toxic or Combustible Gases:
  • Accumulation of gases like methane, carbon monoxide, or other toxic fumes, particularly in confined spaces within excavations.
  • Injuries: Poisoning, explosions, or asphyxiation.

5. Water Accumulation/Flooding

• Sudden Water Inflow:
  • Water can accumulate rapidly in trenches due to rain, broken pipes, or groundwater seepage, trapping and drowning workers.
  • Injuries: Drowning, hypothermia, and asphyxiation.

6. Electrocution

• Contact with Underground Utilities:
  • Accidental contact with buried electric lines during digging can cause electrocution.
  • Injuries: Severe burns, cardiac arrest, neurological damage, and death.

7. Explosions

• Rupturing Gas Lines:
  • Striking underground gas lines during excavation can lead to gas leaks, which may cause explosions or fires.
  • Injuries: Burns, severe trauma, and fatalities.

8. Musculoskeletal Injuries

• Manual Handling and Overexertion:
  • Workers frequently lift heavy tools or materials, leading to musculoskeletal injuries.
  • Injuries: Back strains, sprains, hernias, and repetitive stress injuries.

9. Hypothermia or Heat Stress

• Environmental Conditions:
  • Workers in deep trenches may be exposed to extreme weather conditions like cold or heat, leading to conditions like hypothermia or heat stroke.
  • Injuries: Heat exhaustion, heat stroke, or hypothermia.

These risks underscore the importance of following the company OSHA regulations, implementing protective systems, conducting frequent inspections, and having a competent person on-site to manage trench safety.

To ensure safe working conditions and minimize hazards such as cave-ins, hazardous atmospheres, and falling loads, as required by 29 CFR 1926 Subpart P (Excavations), a systematic approach focusing on key areas is essential:

1. Hazard Identification & Risk Assessment

• Daily Inspections: There should be a designated competent person assigned on every project to inspect excavations, adjacent areas, and protective systems before the start of each shift and after every event (e.g., rainstorms or other incidents) that could increase hazards. Competent Person is assigned by safety or project supervision and CPs shall be trained and experienced in excavation safety.
• Soil Classification: Accurately classify soil conditions to determine the proper protective systems. Use manual tests like pocket penetrometers and visual observations to ensure compliance.

2. Protective Systems for Cave-ins

• Shoring & Shielding: Use appropriate trench boxes or shoring systems to prevent cave-ins. Systems should be designed by a qualified professional and installed according to manufacturer specifications.
• Sloping & Benching: Ensure proper sloping or benching of the trench walls depending on soil type. Follow the prescribed slope angle for different soil types as outlined in the regulations.
• Training and procedures for protective syatems is available at the company safety support center.

3. Safe Access & Egress

• Ladders & Ramps: Ladders, ramps, or other safe means of access and egress for workers in trenches deeper than 4 feet as required by the company procedures is required. Ladders or other means of egress should be located within 25 feet of workers at all times.

4. Hazardous Atmospheres

• Air Monitoring: Test for hazardous atmospheres (oxygen deficiency, toxic fumes, or combustible gases) if the excavation is deeper than 4 feet or if hazardous substances are present.
• Ventilation: Use appropriate ventilation systems to control and eliminate hazardous atmospheres when detected. Implement emergency protocols in the permitting process and provide respirators when necessary.

5. Falling Loads & Vehicle Safety

• Heavy Equipment: Ensure proper safe distances between heavy equipment and the excavation site to prevent falling materials. Use barriers and flags to keep workers clear from areas where loads are being hoisted.
• Material Handling: Store spoil piles and materials at least 2 feet away from trench edges to prevent them from falling into the excavation.

6. Employee Training & Awareness

• Competency Training: Successful completiong of this training module will help to ensure all workers are trained on the hazards of excavation, protective systems, and emergency protocols, including confined spaces and hazardous atmosphere recognition.
• Communication Systems: Develop clear communication protocols to notify workers about potential hazards in real-time, particularly when there are atmospheric or structural changes.

7. Permit System & Compliance

• Permit to Work: It is required that a permit is completed and approved approved for excavations, with the competent person signing off on the protective measures in place before work begins.
• Documentation: All permits including electronic and hand written shall be submitted using the support system form so as to ensure records of inspections, protective systems used, atmospheric tests, and corrective actions taken to ensure compliance with 29 CFR 1926 Subpart P are maintained in our document management system (DMS).

Soil Types and Their Impact on Protective Systems

Understanding soil types is crucial for determining the appropriate protective systems required for excavation work, as outlined by OSHA in 29 CFR 1926 Subpart P. Soils are categorized into three primary types: Type A, Type B, and Type C. Each type has unique stability characteristics that influence the choice of protective systems like sloping, benching, shoring, or shielding.

Soil Types and Stability Characteristics

1. Type A Soil: Highly Stable

• Definition: Type A soil is cohesive with a high compressive strength of 1.5 tons per square foot (tsf) or greater.
• Examples: Clay, silty clay, and clay loam.
• Stability Characteristics:The most stable soil type.
• Resistant to cave-ins under dry conditions and without vibration.
• Protective Systems:Sloping/Benching: The maximum allowable slope for excavations less than 20 feet deep is ¾:1 (53 degrees).
• Shoring/Shielding: Requires lighter protective systems compared to Types B and C because of the soil's stability. Less support is needed to prevent cave-ins.
• Special Considerations: Type A soil can become unstable if fissured, subject to heavy loads or vibrations, or in conditions like previously disturbed ground.

2. Type B Soil: Moderately Stable

• Definition: Type B soil has medium compressive strength, ranging between 0.5 and 1.5 tsf.
• Examples: Silt, silty loam, sandy loam, previously disturbed soils, and medium clay.
• Stability Characteristics:Less stable than Type A but more stable than Type C.
• Susceptible to collapse under pressure or if exposed to vibrations.
• Protective Systems:Sloping/Benching: The maximum allowable slope for excavations less than 20 feet deep is 1:1 (45 degrees).
• Shoring/Shielding: More robust protective systems are required than for Type A soil. Properly designed shoring or trench boxes are recommended to maintain stability.
• Special Considerations: Type B soil is often found in conditions with prior excavation or disturbance, making it more prone to cave-ins.

3. Type C Soil: Least Stable

• Definition: Type C soil has a low compressive strength of 0.5 tsf or less.
• Examples: Gravel, sand, and loamy sand. Also includes soils that are submerged, waterlogged, or subject to seeping.
• Stability Characteristics:The least stable of the soil types, with a high risk of cave-ins.
• Cannot hold its shape and often crumbles easily.
• Protective Systems:Sloping/Benching: The maximum allowable slope for excavations less than 20 feet deep is 1½:1 (34 degrees).
• Shoring/Shielding: Requires the most robust protective systems, such as strong trench boxes or hydraulic shoring, to prevent cave-ins due to the soil’s lack of cohesion.
• Special Considerations: Excavation in Type C soil is particularly dangerous and requires enhanced safety measures due to the rapid deterioration of trench walls.

How Soil Type Affects the Choice of Protective Systems

1. Sloping and Benching:

• The angle of sloping or benching is directly affected by the soil type. More stable soils like Type A allow steeper slopes, while less stable soils like Type C require much shallower slopes to prevent cave-ins.

2. Shoring and Shielding:

• Protective systems like trench boxes or hydraulic shoring must be stronger and more robust for unstable soils (Type B and C) compared to stable Type A soil. Type C soils require the highest level of support due to their tendency to crumble and shift.

3. Depth Considerations:

• Soil stability decreases with increased depth. Even in Type A soil, deeper excavations may require more sophisticated protective systems to counteract the pressures and risks associated with increased depth.

4. Environmental Factors:

• Conditions like moisture, vibrations, and previously disturbed ground can change the classification of soil and, therefore, the required protective systems. For example, dry Type A soil may behave more like Type B if it's exposed to water or vibration.

Benching and sloping are two protective systems used to prevent trench and excavation cave-ins. These systems vary depending on the type of soil (classified as Type A, B, or C) and the depth of the excavation.

1. Sloping Requirements

Sloping involves cutting back the trench walls at an angle inclined away from the excavation to prevent cave-ins. The angle of the slope depends on the soil type and the depth of the trench.

• General Sloping Guidelines:
  • Trenches 5 feet or deeper require sloping unless made in stable rock or a protective system is used (e.g., shoring or trench boxes).
  • The slope angle varies according to soil type as per OSHA's standards in 29 CFR 1926.652.

Soil Type and Sloping Ratios:

• Stable Rock:
  • No slope is required.
  • Vertical trench walls are allowed.
• Type A Soil (Most Stable):
  • Slope ratio: ¾:1 (53-degree angle)
  • For every foot of depth, the trench must be sloped ¾ of a foot back.
• Type B Soil:
  • Slope ratio: 1:1 (45-degree angle)
  • For every foot of depth, the trench must be sloped 1 foot back.

Type C Soil (Least Stable):

• Slope ratio: 1½:1 (34-degree angle)
• For every foot of depth, the trench must be sloped 1½ feet back.

2. Benching Requirements

Benching is a protective system that uses horizontal steps or "benches" to help stabilize the trench walls. Benching can be used in combination with sloping to prevent cave-ins. However, OSHA only allows benching in certain soil types.

• General Benching Guidelines:
  • Benching is not permitted in Type C soil, which is the least stable.
  • Benching can be used for Type A and Type B soils.
  • The benching configuration must follow specific height and width requirements based on soil type.

Benching Configurations:

Type A Soil:

• The trench can have multiple horizontal benches.
• Each bench must be no higher than 4 feet.
• The overall angle of incline, including benching, must be equal to or less than a slope of ¾:1 (53 degrees).

Type B Soil:

• Benching can still be used, but the overall angle of incline, including benching, must be equal to or less than a slope of 1:1 (45 degrees).
• Similar to Type A, benches must not exceed 4 feet in height.

Type C Soil:

Benching is not allowed due to the unstable nature of this soil type.

3. Key Considerations

• Depth: Trenching systems are required in trenches that are 5 feet or deeper, unless the excavation is made entirely in stable rock.
• Competent Person: A competent person must assess the soil and determine the appropriate protective system (sloping, benching, shoring, or shielding).
• Hazard Prevention: Workers must stay within the sloped or benched area and away from the edges to avoid falling into the trench or being caught in a cave-in.

By following these guidelines, workers can be better protected from cave-ins and other trenching hazards.

How Soil Affects the Selection of Protective Systems

The more unstable the soil, the more robust and extensive the protective system needs to be:

• Stable Soils (Type A):
  • Simple sloping and benching systems can be used due to the soil's ability to hold its shape. However, deeper trenches may still require additional protective measures like shoring.
• Moderately Stable Soils (Type B):
  • A combination of sloping and benching can be used, but with a more cautious approach. Protective measures like shoring or shielding are frequently used, especially for deeper excavations.
• Unstable Soils (Type C):
  • The most stringent protective measures are necessary, including sloping at very shallow angles or using trench boxes and hydraulic shoring. Sloping alone often cannot provide sufficient protection due to the high risk of cave-ins.

Pre-excavation planning is essential for ensuring safety and compliance during trenching and excavation projects. It involves identifying potential hazards, preparing protective measures, and setting clear procedures before digging begins. Here’s a detailed breakdown of the key components:

1. Conducting Utility Locates: Marking Underground Utilities (Call 811)

Importance:

Before any excavation begins, it's critical to locate and mark underground utilities, such as gas lines, electrical cables, water lines, sewer systems, and communication lines. Striking underground utilities can result in severe injuries, service disruptions, and costly damages. Calling 811 is a nationwide service in the U.S. that connects excavators with utility companies to mark underground utilities.

Steps for Utility Locates:

• Call 811:
  • Call at least 48-72 hours before starting excavation (depending on local requirements).
  • Provide detailed information about the project, including location, size, and scope of work.
  • The utility locator service will contact local utility companies, which will dispatch technicians to mark the utility locations with color-coded paint, flags, or stakes on the ground.

Wait for Marking:

• Do not start digging until all utilities are marked or you receive confirmation that the area is clear.
• Marked areas should be avoided or carefully dug using non-destructive techniques (e.g., vacuum excavation or hand digging).

Color Codes for Utility Markings:Red: Electric power lines

• Yellow: Gas, oil, steam, petroleum
• Orange: Communication lines, cables, TV
• Blue: Potable water
• Green: Sewers and drain lines
• White: Proposed excavation area
• Pink: Temporary survey markings

Document and Verify:

• Once marked, take photos and document the utility locations to ensure reference throughout the project. Verify the location of utilities by carefully exposing them if necessary.

2. Identify Entry/Exit Points and Traffic Control

Entry/Exit Points:

Planning for safe access and egress to and from the excavation site is essential for worker safety. Properly designed entry and exit points prevent falls, trips, and slips, and ensure workers can quickly exit in case of emergencies.

Steps for Identifying Entry/Exit Points:

• OSHA Requirement: Trenches 4 feet or deeper must have a safe means of entry and exit, such as ladders, ramps, or stairways.
• Locate Access Points:
  • Ladders: Place ladders at intervals no more than 25 feet from any worker in a trench to ensure they can reach an exit quickly.
  • Ramps/Stairways: Ensure ramps or stairways are sturdy, well-constructed, and free from obstructions or hazards.
• Inspection:
  • Regularly inspect entry/exit points for damage, shifting, or degradation, especially after rain or use.

Traffic Control:

For projects near roads or in high-traffic areas, implementing a traffic control plan is vital to protect both workers and the public.

Steps for Traffic Control:

• Establish Work Zones: Clearly define and separate the work zone from pedestrian and vehicle traffic using cones, barricades, and signs.
• Signage:
  • Use proper warning signs before the excavation zone to inform drivers and pedestrians of the work ahead.
  • Signs should comply with local Department of Transportation (DOT) standards and be visible from a distance.
• Flaggers and Spotters:
  • In areas where traffic flows through or near the work zone, assign flaggers to direct vehicles and keep the area safe.
  • Use spotters when operating heavy equipment near the excavation to prevent vehicle and equipment collisions.
• Vehicle Access:
  • Plan and designate separate vehicle entry/exit points to reduce the risk of accidents near the excavation site.
  • Ensure proper barriers or controls for vehicles to avoid them falling into open excavations.

3. Ensure Your Project Has an Emergency Action Plan (EAP)

Importance:

An Emergency Action Plan (EAP) is a comprehensive procedure that outlines the steps workers must take in the event of an emergency, such as a cave-in, equipment failure, hazardous gas release, or contact with underground utilities. It is critical for minimizing injuries, ensuring worker safety, and coordinating an effective emergency response.

Steps for Developing an Emergency Action Plan:

Go to the Safety tab of the safety support center and click on the Emergencies link. Then click on the Emergency Action Planner. This tool will walk you through the necissary inputs required for developing an EAP.

• Identify Potential Emergencies:
  • Assess the job site for specific risks such as cave-ins, flooding, exposure to hazardous gases, utility strikes, or vehicle accidents.
• Develop Procedures for Each Emergency:
  • Clearly outline the steps workers should take in the event of an emergency.
  • Include instructions on how to shut down equipment, evacuate workers, administer first aid, and contact emergency services.
• Assign Responsibilities:
  • Designate key personnel responsible for leading emergency actions, such as site supervisors or competent persons.
  • These individuals should be trained to direct emergency procedures and make critical decisions quickly.
• Emergency Evacuation Plan:
  • Clearly define evacuation routes from the excavation site.
  • Ensure exit points (ladders, ramps, stairways) are accessible and unobstructed for a quick and safe evacuation.
  • Conduct drills to practice the emergency evacuation plan with workers.
• First Aid and Rescue Equipment:
  • Equip the site with first aid kits, stretchers, and emergency breathing apparatus if necessary.
  • Ensure workers have access to personal protective equipment (PPE), such as fall protection harnesses or respiratory protection, for emergencies.
• Communications Plan:
  • Ensure workers know how to quickly contact emergency services (911).
  • Provide backup communication methods (radios or satellite phones) if working in remote areas.
• Utility-Strike Response:
  • Develop a specific action plan if underground utilities are struck, including immediate evacuation and notification of utility companies to shut down lines.
• Rescue Operations:
  • Ensure that workers are trained in non-entry rescue techniques if possible (e.g., pulling workers out of the trench without entering).
  • If trench entry is required for rescue, ensure that only trained rescue personnel enter, following confined space and rescue protocols.
• Coordination with Local Emergency Services:
  • Before starting excavation, inform local emergency responders of the worksite location and potential hazards.
  • Ensure they are familiar with the site layout and can respond quickly if needed.

By thoroughly addressing utility locates, safe entry/exit points, traffic control, and having an emergency action plan in place, the risk of accidents and injuries during trenching and excavation work can be significantly reduced. These steps help ensure worker safety and compliance with OSHA standards.

Emergency Procedures

The Emergency Action Plan (EAP) should be used in conjunction with the Job Hazard Analysis (JHA) and the Trenching and Excavation Permit to establish and communicate emergency procedures before work begins.

Pre-job planning, using these tools, ensures workers are properly trained on evacuation and rescue protocols. Various training resources are available to meet the requirements. Completing the assigned training modules listed in the Training Matrix provided by the Support Center will ensure you have the necessary awareness and knowledge to safely participate in trenching and excavation activities.

First Aid and Rescue Operations

• Ensure appropriate first aid supplies are readily available on-site.
• Rescue equipment must be easily accessible for deep trench emergencies. In some cases, it may be necessary to subcontract rescue services or have the local fire department provide standby rescue services on-site.

Cave-in Rescue Considerations

Only trained professionals should attempt to rescue individuals trapped in a cave-in to prevent further injuries or fatalities. If an employee becomes trapped in a cave-in, emergency services must be contacted immediately.

Trenching & Excavation Permits:

• A Trenching and Excavation Permit is required whenever an excavation exceeds 4 feet in depth and will be entered by a worker, and anytime an exvacation will reach 20 feet or more in detpth.
• Permits are available on the safety support center under the Safety tab in the Permits link.
• Paper and written permits must be shared through the same online resource.

Recordkeeping Requirements:

• All permits and inspections will submitted through the electronic system and records are automatically stored via the built-in document management system. 

Real-World Example: The 2016 Boston Trench Collapse

Incident Summary:

In October 2016, two workers were killed in a trench collapse in Boston, Massachusetts. The workers were installing a new water pipe in an unshored trench that was approximately 12 feet deep. During the work, a section of the trench wall collapsed, burying both men. Adding to the tragedy, the trench quickly filled with water, drowning the workers before rescue teams could reach them.

What Went Wrong:

1. Lack of Protective Systems:

• The trench was not properly protected with a trench box, shoring, or sloping to prevent cave-ins. OSHA regulations require trenches deeper than 5 feet to have protective systems, but none were in place.

2. Inadequate Pre-Planning and Hazard Identification:

• The workers were not properly trained or briefed on the specific hazards of trenching work. The employer failed to conduct a thorough Job Hazard Analysis (JHA), which could have identified the need for proper protective systems and additional safety measures.

3. Failure to Monitor Site Conditions:

• The trench was dug in unstable soil conditions near a water main, which increased the risk of collapse. The employer did not account for these factors or monitor changing soil conditions, especially given the risk of water accumulation.

4. Emergency Response and Rescue Planning:

• There was no effective emergency action plan in place. When the collapse occurred, workers on site were not trained to perform immediate rescues or had the proper equipment to attempt non-entry rescue methods safely.

How It Could Have Been Prevented:

1. Use of Proper Protective Systems:

• A trench box or appropriate shoring should have been used to support the trench walls. OSHA mandates the use of protective systems for trenches deeper than 5 feet unless the excavation is made entirely in stable rock. Sloping or benching the trench walls could have also prevented the collapse by reducing the weight exerted on the trench.

1. Pre-Excavation Planning and Training:

• A thorough Job Hazard Analysis (JHA) should have been conducted to assess the risks associated with trenching. Workers should have been trained on recognizing trench hazards, protective system requirements, and proper safety protocols. Conducting utility locates and ensuring no water main risks were involved should have been part of the pre-planning process.

2. Soil Testing and Monitoring:

• A competent person should have been assigned to conduct regular soil analysis and monitor conditions in the trench. If the competent person had observed changes in soil stability or water infiltration, work could have been paused until the necessary precautions were taken.

3. Emergency Action Plan (EAP):

• The employer should have developed a clear emergency action plan that included procedures for trench collapse scenarios, rescue protocols, and coordination with emergency services. Workers should have been trained to recognize the signs of an imminent collapse and to evacuate immediately. The plan should have outlined non-entry rescue methods in case of a cave-in, as well as how to manage water-related hazards in the trench.

A Safe Trench