Excavation and Trenching Explanations - 1ShoppingCart.com · 2017-08-15 · Excavation and...

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.

©MiCAH Safety Solutions, LLC

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


Are Damaged Utilities

Really A Big Deal?


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


Identifying Utilities

Utility Markers Color Coded Paint Marking Flags


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


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.


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.


Two Buried Workers

Buried Worker

What Else Do You See?


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.


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


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


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


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


Implement Protective Systems

Shoring Sloping Shielding


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)


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.


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.


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


Safe or Unsafe?


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.


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


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.


This is What We Are Trying to Prevent


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Excavation and Trenching Explanations - 1ShoppingCart.com · 2017-08-15 · Excavation and...

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