More than 800 construction workers are involved in accidents each year on the job. Of these accidents, approximately 40 workers are involved in an incident related to excavation or trenching. That is why the Occupational Safety and Health Administration (OSHA) has gone to great lengths to define threats and identify safe practices. Fortunately, a little knowledge goes a long way when it comes to safe excavations and earth removal.
Trenching and Excavating 101: What to Watch Out For
When it comes to trenching and excavating, you must have a thorough understanding of the most significant risks posed by these operations. One of the primary threats associated with trenching and excavating is cave-ins, accounting for most worker injuries and fatalities. Trench collapses lead to dozens of deaths and hundreds of injuries annually. Other potential issues include hazardous atmospheres, falls, falling loads, and incidents involving mobile equipment.
The best guard against these potential hazards is to never enter a construction site without the proper protective gear or a trench that fails to have the right protective systems in place.
Trenching and Excavation Safety Systems
A protection system should always be in place for commercial trenches five feet or deeper. The only exception is an excavated trench comprised of stable rock. Once a trench reaches a depth of twenty feet, its safety system must be designed by a registered engineer, or tabulated data that has been prepared or approved by such an expert. Different types of protective systems exist.
SHORING is installing supports to prevent cave-ins and soil shifting.
SLOPING is cutting back the trench wall at an angle inclined away from the excavation.
SHIELDING relies on trench boxes or other support types to avoid sediment cave-ins.
BENCHING protects employees from cave-ins by removing earth from the excavation sides to form one or more horizontal steps or levels and cannot be used in Type C soils.
How to Select the Best Safety System
The decision-making process for choosing the right safety system can be complicated, involving multiple considerations, including:
• Changes due to weather or climate
• Other operations in the vicinity
• Surcharge loads (may include materials used in the trench or spoil)
What to Know about Soil Types
Excavation safety requires a competent person onsite who understands different soil types and can guide you through the process of installing the best safety system for specific soil conditions. OSHA relies on three tests. At least two of these tests should be implemented any time soil conditions may change.
Granular soils contain coarse particles like gravel or sand. As a result, the dirt does not stick together and therefore requires more extraordinary measures to prevent a cave-in.
Cohesive soils include enough clay or fine particles that individual particles stick together. Cohesive soil is less likely to cave in.
OSHA relies on a measurement known as unconfined compressive strength (the amount of pressure it requires to collapse a specific soil type) to categorize each soil type.
STABLE ROCK is natural solid mineral matter. You can excavate with vertical sides and it remains intact while exposed. Stable rock is the safest soil in which to work because there are no individual particles that could separate or cave in.
TYPE A, the next most stable of the soil types, is highly cohesive and boasts a high unconfined compressive strength (1.5 tons per square foot or more). Type A soils include clay, silty clay, sandy clay, and clay loam.
TYPE B soil is cohesive but has been disturbed or otherwise fissured. It is characterized by particles that refuse to stick together mixed with Type A soil. Type B soil demonstrates medium unconfined compressive strength (0.5 – 1.5 tons per square foot) and includes silt, silt loam, angular gravel, and soil located near sources of vibration or marked by fissures.
• TYPE C soil is the least stable. Its granular soil particles do not stick together. It has a low unconfined compressive strength (0.5 tons per square foot or less) and includes sand and gravel as well as soil with clear signs of water seepage.
Consistently monitor for changing conditions as exposure to vibrations or precipitation can lead to changing soil conditions and require different safety systems.
Daily Inspections by a Competent Employee
Inspections must occur before workers enter the excavation area or trench to help eliminate the risk of excavation hazards. OSHA defines a competent person as an individual capable of identifying predictable and existing hazards or working conditions that are considered unsanitary, dangerous, or hazardous to workers. A competent person will:
• Inspect protective systems
• Monitor water removal equipment
• Design structural ramps
• Conduct site inspections
• Take speedy action and corrective measures to mitigate potential hazards
Understanding Access and Egress Points
The designated competent person regularly inspects excavations and trenches four feet or deeper to ensure safe access and egress. Means of entry and escape must lie within 25 feet of employees.
Following these OSHA guidelines ensures the safest working conditions for all employees on a job site.
• Maintain surcharge loads a minimum of two feet away from trench edges
• Keep heavy equipment away from trench edges
• Know where all underground utilities are located
• Test for low oxygen, toxic gases, and hazardous fumes
• Inspect trenches at the beginning of each shift
• Never work under raised loads
• Inspect earthworks after rainstorms and other precipitous weather
• Inspect trench after any occurrence impacting conditions
• Ensure all personnel wear high visibility clothing when exposed to vehicular traffic
Whether your construction company has one year of experience or two decades in trenching, backfilling jobs, and shoring, approach each new job with meticulous preparation and care. The root of most on-the-job accidents is a lack of initial planning. Do not wait until work commences to figure out the best safety system for an excavation or trench as making adjustments to fix sloping and shoring issues will slow your operations and increase your project costs. Putting a band-aid on potential safety issues increases the likelihood of an excavation failure or cave-in down the road.
Safety Factors to Consider Before Bidding
Before preparing a bid, understand the safety issues at the job site. Know what materials and equipment employees need on hand to comply with OSHA safety standards. This safety checklist can help evaluate each job site before drawing up a plan. • Proximity and physical condition of nearby structures
• Ground and surface water
• Location of the water table
• Underground and overhead utilities
• Quantity of protective systems or shoring that may be required
• Number of ladders needed
Taking test borings for soil conditions and types, observations, job site studies, consultations with utility companies, and meetings with local officials can all help determine the kind, amount, and cost of safety equipment needed for workers to do their jobs properly, safely, and more cost-effectively.
Promoting Excavation at Your Workplace
Trenching and excavation are among the two most dangerous activities at construction sites. For this reason, you must approach both with great care. OSHA lays out a comprehensive system of regulations to help ensure the safety of workers.
From employing a competent person at your job site to understanding soil types and safety system implementation, these precautions translate into a safer workplace.
Ankit Sehgal is the Chief Executive Officer at Swiftdrain, a global drainage and infrastructure products manufacturing company. He oversees all product design and development at the firm, including engineering, materials sourcing, and production. For more, visit swiftdrain.com.