excavation and trenching explanations - 1shoppingcart.com · 2017-08-15 · excavation and...
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Excavation and Trenching
Explanations
OSHA Introduction: 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. An unprotected trench can be an early grave. 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.
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Excavation Equipment
Outline of Dangers and Precautions
Never Stand In A Swing Path Always Avoid Pinch Points Use Spotters As Needed
Never Get Under A Load Always Use Tag Lines
Stay Out Of Line Of Fire
Equipment Can Turn Over Ensure Solid Ground
Watch Equipment Near Edges
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Are Damaged Utilities
Really A Big Deal?
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Gas, Petroleum, Chemicals, and Acids
Excavator Struck a 10” Gas Main Worker Burned Over 70% of Body
Maryville, Illinois
Materials can be Highly Volatile
One Spark is All it Takes
Even Static Electricity can Ignite
Explosions can be Catastrophic
Greatest Danger to the Public
Don’t Risk It, Check It
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Identifying Utilities
Utility Markers Color Coded Paint Marking Flags
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A Final Warning!
If You Discover Tape, Treat It As If A Utility Is Directly Below Use Hand Digging Or Non-Intrusive Excavation To Expose The Utility
Do Not Continue The Equipment Excavation Never Assume Utilities Will Always Have Marking Tape
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The Anatomy of a Cave-In
Distress means that the soil is in a condition where a cave-in is imminent or is likely to occur. Warning Signs:
The development of fissures in the face or adjacent to excavation. The subsidence of the edge of an excavation. The slumping of material from the face of an excavation. The bulging or heaving of material from the bottom of excavation. The spalling of material from the face of an excavation. Small amounts of material suddenly separating from the face of an
excavation and trickling or rolling down into the excavation.
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OSHA Overview of Soil Mechanics Figure V:2-3. Toppling
This figure illustrates how toppling occurs when the trench's vertical face shears along the tension crack line and topples into the excavation.
Figure V:2-4. Subsidence and Bulging This figure illustrates how an unsupported excavation can create an unbalanced stress in the soil, which, in turn, causes subsidence at the surface and bulging of vertical face of trench.
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Two Buried Workers
Buried Worker
What Else Do You See?
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But it’s Just a Little Hole
37%
26%
26%
11%
Depth in Feet
0-5' 6-10'
11-15' 16-20'
26% for depths of 6-10”
37% of All Trenching
Accidents Occur at Depths 5’ or Less
Trench Accidents by Depth
Why 0-10’?
These are the most common work depths. Safety is often neglected because of the more shallow depth.
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Preventing Cave-Ins
Evaluate Work Area and Excavation Conditions for Hazards
Competent Person Must Evaluate Required Materials
Determine Soil Type and Classification Excavations Over 5‘ Must Have a Protective System
Support/Shoring Systems, Sloping and Benching, Shielding
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Determining the Soil Type
Soil Classification Must Be Performed By A Competent Person
Visual Test
Check Entire Work Area For Hazards Look For; Fissured Ground Layered Soil Disturbed Earth Seepage Water Runoff Potential Inadequate Drainage Vibration Soil composition and substance
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Type B – Includes cohesive soil with an unconfined compressive strength greater than 0.5 tsf (48 kPa) but less than 1.5 tsf (144 kPa) and granular cohesion less soils (such as angular gravel, similar to crushed rock, silt, silt loam, sandy loam, and, in some cases, silty clay loam and sandy clay loam).
*See Appendix A to Subpart P of Part 1926, paragraph (b) — Definitions (Type B), for a detailed definition of Type B soil.
Angular Gravel Soil
Silt
Silt Loam
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Soil Composition Analysis
Unconfined compressive strength means the load per unit area at which a soil will fail in compression. It can be determined by laboratory testing or estimated in the field using a pocket penetrometer, thumb penetration tests, or other methods.
Some Methods of Testing
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Implement Protective Systems
Shoring Sloping Shielding
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MAXIMUM ALLOWABLE SLOPES
SOIL OR ROCK TYPE
MAXIMUM ALLOWABLE SLOPES (H:V)(1) FOR EXCAVATIONS LESS THAN 20 FEET DEEP(3)
STABLE ROCK TYPE A (2) TYPE B TYPE C
VERTICAL (90º) 3/4:1 (53º) 1:1 (45º) 1 ½:1 (34º)
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Shoring Systems
There are many different types, configurations, and applications. Refer to the OSHA Standard; 1926 Subpart P App C,D,E, and F for specifications.
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Aluminum Pneumatic Shoring Systems
Top Priority- Follow Manufacturers Guidelines
• Deviation from Guidelines Require Written Approval • Protective Systems Selection in Accordance with OSHA • Use Tabulated Data Such as Tables and Charts • Systems Must be Securely Connected in Every Part • Protect Employees Against Struck By, Pinch Points,
Overhead, and Falls During Installation • Excavation of material to a level no greater than 2 feet
below bottom of support system. • Not Subject to loads exceeding the systems capability. • Competent Person Must Inspect After Damage Occurs • Removal of the system begins at and progresses from the
bottom of the excavation. • Backfilling shall progress together with the removal of
support systems from excavations. ©MiCAH Safety Solutions, LLC
Water Accumulation Hazards
1926.651(h)(1) Employees shall not work in excavations in which there is accumulated water, or in excavations in which water is accumulating, unless adequate precautions have been taken to protect employees against the hazards posed by water accumulation. The precautions necessary to protect employees adequately vary with each situation, but could include special support or shield systems to protect from cave-ins, water removal to control the level of accumulating water, or use of a safety harness and lifeline.
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Hazardous Atmospheres
Some Causes to Recognize
Equipment and Vehicle Exhaust
Sewer Gas Accumulation
Damaged Utilities
Nearby Operating Facilities
Welding and Compressed Gas Use
Fire and Smoke
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Safe or Unsafe?
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Ladders- Ingress and Egress
What about this ladder? Ladders must extend 3’ above any
excavation or surface. Must be secured in place, top and
bottom to prevent sliding/movement. Lateral travel distance no more than
25’. Multiple ladders lashed together
cannot be used. Must be free of defects, damage, and
hazards. Must be inspected prior to use. Ladders on a 4/1 slope when possible.
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Stability of Adjacent Structures
OSHA- 1926.651(i)
Evaluate Work Area Before Excavation Determine Possible Structure Hazards Verify Stability Of Structures Sidewalks, Pavements, Etc. Consider Possible Undermining Protective Systems For Workers Shoring, Bracing, Underpinning Prevent Collapse Of Structures
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Safety Training Review
Key Focus Points
Keep heavy equipment away from trench edges. Maintain communication around equipment. Keep surcharge loads at least 2 feet from edges. Know where underground utilities are located. Test for low oxygen, hazardous fumes and toxic gases. Inspect trenches start of each shift, and after heavy rain. Implement and use an Excavation Daily Checklist. Protect water ways from environmental hazards. Do not work under raised loads. Employees must be protected from lose rock or soil. Ensure adequate protection based on soil conditions. Use proper means of entry and exit to the excavation.
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This is What We Are Trying to Prevent
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