Excavation Hazards
Injury and Death
Excavating is one of the most hazardous construction operations
Most accidents occur in trenches 5-15 feet deep
There is usually no warning before a cave-in
Definitions
Excavation – a man-made cut, cavity, trench, or depression formed by earth removal.
Trench – a narrow excavation. The depth is greater than the width, but not wider than 15 feet.
Shield - a structure able to withstand a cave-in and protect employees
Shoring - a structure that supports the sides of an excavation and protects against cave-ins
Sloping - a technique that employs a specific angle of incline on the sides of the excavation. The angle varies based on assessment of impacting site factors.
Focus of Training
The discussion of this topic covers four main points. At the conclusion of the training, you should be able to:
1. State the greatest risk that is present at an excavation.
2. Briefly describe the three main methods for protecting employees from cave-ins.
3. Name at least three factors that pose a hazard to employees working in excavations, and at least one way
to eliminate or reduce each of the hazards.
4. Describe the role of a competent person at an excavation site.
Protection of Employees
Employees should be protected from
cave-ins by using an adequately designed
protective system
Protective systems must be able to resist all expected loads to the system
Requirements for Protective Systems
A well-designed protective system
Correct design of sloping and benching systems
Correct design of support systems, shield systems, and other protective systems
Plus
Appropriate handling of materials and equipment
Plus
Attention to correct installation and removal
Equals Protection of employees at excavations
Design of Protective Systems
The employer shall select and construct :
slopes and configurations of sloping and benching systems
support systems, shield systems, and other protective systems
Shield - can be permanent or portable. Also known as trench box or trench shield.
Shoring - such as metal hydraulic, mechanical or timber shoring system that supports the sides
Sloping - form sides of an excavation that are inclined away from the excavation
Protect Employees Exposed to Potential Cave-ins
Slope or bench the sides of the excavation,
Support the sides of the excavation, or
Place a shield between the side of the excavation and the work area
Cave-in Hazard
This excavation has inadequate support posts and egress access
Inadequate Protective System
This worker is in a trench with no protective system, that is not sloped or benched and has no means of egress
Factors Involved in Designing a Protective System
Soil classification
Depth of cut
Water content of soil
Changes due to weather and climate
Other operations in the vicinity
Shoring
General
Provides a framework to work in
Uses wales, cross braces and uprights
Supports excavation walls
OSHA tables provide shoring data
Must know soil type
Must know depth and width of excavation
Must be familiar with the OSHA Tables
Trench Shield
A trench shield was built around this work area
Hydraulic Trench Support
Using hydraulic jacks the operator can easily drop the system into the hole
Once in place, hydraulic pressure is increased to keep the forms in place
Trench pins are installed in case of hydraulic failure
Materials and Equipment
Equipment used for protective systems must not have damage or defects that impair function.
If equipment is damaged, the competent person must examine it to see if it is suitable for continued use.
If not suitable, remove it from service until a professional engineer approves it for use.
Protection from Vehicles
Install barricades
Hand/mechanical signals
Stop logs
Grade soil away from excavation
Fence or barricade trenches left overnight
Hazardous Conditions
The weight and vibrations of the crane make this a very hazardous condition.
They should not be working under this crane.
Spoils
Measure from nearest part of the spoil to the excavation edge
Place spoils so rainwater runs away from the excavation
Place spoil well away from the excavation
Water accumulation
•
Oxygen deficiency
•
Toxic fumes
•
Access/Egress
•
Falls
•
Mobile equipment
Water is Hazardous
-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.
-If water is controlled or prevented from accumulating by the use of water removal equipment, the water removal equipment and operations shall be monitored by a competent person to ensure proper operation.
-If excavation work interrupts the natural drainage of surface water (such as streams), diversion ditches, dikes, or other suitable means shall be used to prevent surface water from entering the excavation and to provide adequate drainage of the area adjacent to the excavation.
Hazardous Atmosphere
Must also test where oxygen deficiency or a hazardous atmosphere could reasonably be expected to exist, before an employee enters the excavation.
If hazardous conditions exist, controls such as proper respiratory protection or ventilation must be provided. Also, controls used to reduce atmospheric contaminants to acceptable levels must be tested regularly.
Where adverse atmospheric conditions may exist or develop in an excavation, the employer also must provide and ensure that emergency rescue equipment, (e.g., breathing apparatus, a safety harness and line, basket stretcher, etc.) is readily available. This equipment must be attended when used.
Employees shall not be permitted to work in hazardous and/or toxic atmospheres. Such atmospheres include those with:
-- less than 19.5% oxygen,
-- a combustible gas concentration greater than 20% of the lower flammable limit, and,
-- concentrations of hazardous substance that exceed those specified in the Threshold Limit Values for airborne contaminants established by the ACGIH.
Means of Egress
A stairway, ladder, or ramp must be present in excavations that are 4 or more feet deep, and within 25 feet of the employees
Protection from Falls, Falling Loads, and Mobile Equipment
Install barricades
Use hand / mechanical signals
Grade soil away from excavation
Fence or barricade trenches left overnight
Use a flagger when signs, signals and barricades are not enough protection
Competent Person
Must have had specific training in and be knowledgeable about:
Soils classification
The use of protective systems
The requirements of the standard
Must be capable of identifying hazards, and authorized to immediately eliminate hazards
Inspections of Excavations
A competent person must make daily inspections of excavations, areas around them and protective systems:
Before work starts and as needed,
After rainstorms, high winds or other occurrence which may increase hazards, and
When you can reasonably anticipate an employee will be exposed to hazards.
Inspections of Excavations
If the competent person finds evidence of a possible cave-in, indications of failure of protective systems, hazardous atmospheres, or other hazardous conditions:
Exposed employees must be removed from the hazardous area
Employees may not return until the necessary precautions have been taken
Site Evaluation Planning
Before beginning excavation:
Evaluate soil conditions
Construct protective systems
Test for low oxygen, hazardous fumes and toxic gases
Provide safe in and out access
Contact utilities
Determine the safety equipment needed
-The greatest risk in an excavation is a cave-in.
-Employees can be protected through sloping, shielding, and shoring the excavation.
-A competent person is responsible to inspect the excavation.
-Other excavation hazards include water accumulation, oxygen deficiency, toxic fumes, falls, and mobile equipment.
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Description : Excavation Hazards Injury and Death Excavating is one of the most hazardous construction operations Most accidents occur in trenche...
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