Course Duration: 3 Hours

Burnt Mountain LLC. Learning Management System (BMLMS)

This training is based on the requirements of CFR 1926 Subpart P ‑ Excavations

BEFORE DOING ANY DIGGING CALL 811! 

 

Each year employees are killed while working in and around excavations and trenches.  Cave-ins are the leading hazard when working within a trench, therefore, project management should take the appropriate protective measures to provide for the safety of those employees required to work in and around excavations and trenches.

This presentation is designed to provide individuals with information on related OSHA regulations as well as methods to ensure the safety of those who may enter or work around excavations and trenches.

This presentation is not a substitute for any of the provisions of the Occupational Safety and Health Act of 1970 or for any standards issued by the U.S. Department of Labor. 

The following topics will be addressed in this program:

• Excavation and Trenching Hazards
• Protection of Employees
• Protective Systems Design
• Cave-in Hazards
• Competent Person
• Inspection of Excavations
• Site Evaluation Planning

The discussion of this topic covers four main points.  At the conclusion of the training, you should be able to:

• State the greatest risk that is present at an excavation.
• Briefly describe the three main methods for protecting employees from cave-ins.
• 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.
• Describe the role of a competent person at an excavation site.

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 (shield system) -- a structure able to withstand a cave-in and protect employees with the structure.  Shields can be permanent structure or can be designed to be portable and moved along as work progresses.  Also known as a trench box or trench shield.

Shoring (shoring system) -- a structure such as a metal hydraulic, mechanical or timber shoring system that supports the sides of an excavation and which is designed to prevent cave-ins.

Sloping (sloping system) -- protects employees from cave-ins by excavating to form sides of an excavation that are inclined away from the excavation to prevent cave-ins.  The angle of incline varies with differences in such factors as the soil type, environmental conditions of exposure, and application of surcharge loads.

The “Competent Person” must have had specific training in and be knowledgeable about:

• Soils classification
• The use of protective systems
• The requirements of the
    standard

A competent person must be capable of identifying hazards and authorized to immediately eliminate them.

 

Other hazards include:

• Asphyxiation due to a lack of oxygen
• Inhalation of toxic materials
• Moving machinery near the edge of the excavation can cause a collapse
• The accidental severing of underground utility lines
• Fire

OSHA Standard Exemptions:

House foundation/basement excavations (including those that become trenches by definition when formwork, foundations, or walls are constructed) are exempt from the OSHA standard.  The specific information regarding the interpretation of this exemption may be found on the OSHA public web site.  Reference 29 CFR 1926.652.

 

The exemption specifies height and width for the excavation, impact of water and environmental conditions, soil and equipment factors, and operation of heavy equipment in the vicinity.

• 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.

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.

Reference CFR 1926.652(a)

Protective system – a method of protecting employees from cave-ins, from material that could fall or roll from an excavation face or into an excavation, or from the collapse of adjacent structures.  Protective systems include support systems, sloping and benching systems, shield systems, and other systems that provide the necessary protection.

Spoil pile (surcharge) – material (soil or rock) removed from the cut which, after completing the underground work, will be returned to cover-up the excavation.

Different soils can have a drastic impact on how a project area is excavated. Knowing these soil types and how excavation practices affect the area helps you approach your project safely.

 

There are three classes of soil: Type A, Type B or Type C.

 

Type A soils include clay, silty clay, sandy clay and clay loam. This soil type is the most stable soil as far as excavation is concerned. The only exception would be if the soil is fissured or has been previously disturbed. It can also become unstable if water is seeping through it or if it has been subjected to vibrations from heavy traffic or pile drivers.

 

Type B Soils include angular gravel, silt, and silt loam. These soils often have been cracked or disturbed causing the soil to not stick together as well as a Type A soil would. Type B soils also include soils that would be classified as Type A, but they have been fissured or near sources of vibration.

 

The least stable of the soil types is Type C soils. These include gravel and sand. Soil with water seeping through creates instability and therefore are automatically classified as Type C soils regardless of soil type.

 

It’s important to remember that excavation areas can have all three soil types in different layers of the soil. The least stable layer determines the classification of that excavation area.  As you begin your excavation project, perform a visual test of the construction site. A visual inspection of the area will help determine any factors that will lower the strength of the soil. For example, if a soil comes out in clumps as it is being excavated, it is a cohesive soil and creates a stable environment for excavation. Other things to look for include sources of vibration near the excavation site, previously disturbed soil, or signs of water seeping through the soil. You can also look for crack-like openings or chunks of soil that crumble off. If any of these signs are present, the soil is an unstable soil type.

 

Choosing a good soil sample is key to performing a soil test. A sample should be typical of the surrounding soil in the excavation area. Additional soil tests should be conducted as the excavation deepens. Test the soil from the excavation pile, provided it is fresh soil and has not been compacted in any way. Dried soil samples produce different soil test results so testing with fresh soil is highly recommended.

 

A thumb penetration test can be used for all three soil types. However, Type A soils typically only show an indentation is the soil with a thumb penetration test. On the other hand, a Type C soil can be easily penetrated with a thumb penetration test. As conditions change, soil must be reclassified.

 

You can also test the soil using the plasticity method or the pencil test to see if the soil is cohesive. Another testing method is through the use of the pocket penetrometer. The pocket penetrometer provides a numerical number to the soil sample.

For a more comprehensive review of soil testing, you can view this video provided by OSHA:

A well-designed protective system

Correct design of:

- sloping and benching systems
- support systems
- shield systems
- other protective systems
+
Appropriate handling of materials and equipment
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Attention to correct installation and removal
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Protection of employees at excavations

Several factors come into play when developing a total “protective system”.  The design of the system itself, how materials and equipment are handled in and around the excavation, and installation and removal of protective system components.

The project team 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

Added means of protection include:

• Benching- excavating the sides of an excavation to form one or a series of horizontal levels or steps, usually with vertical or near-vertical surfaces between levels.
• Shoring or shielding- is used when the location or depth of the cut makes sloping back to the maximum allowable slope impractical. There are two basic types of shoring, timber and aluminum hydraulic.
• Trench boxes (shielding)- are different from shoring because instead of supporting the trench face, they are mostly serve to protect workers from cave-ins.  The excavated area between the outside of the trench box and the face of the trench should be as small as possible.  The space between the trench box and the excavation side may be backfilled (or other means may be used) to prevent lateral movement of the box.  Shields may not be subjected to loads exceeding those which the system was designed to withstand.  Trench boxes may be used in combination with sloping and benching.

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.

Reference 1926.652(b) Design of sloping and benching systems:

(1)Each employee in an excavation shall be protected from cave-ins by an adequate protective system except when:
(i)Excavations are made entirely in stable rock; or
(ii)Excavations are less than 5 feet in depth and examination of the ground by a competent person provides no indication of a potential cave-in.
(2)Protective systems shall have the capacity to resist without failure all loads that are intended or could reasonably be expected to be applied or transmitted to the system.

This excavation has inadequate support posts and egress access.

Reference 1926.652(a) and 1926.652(c)(1)

Designs for aluminum hydraulic shoring shall be in accordance with paragraph (c)(2), but if the manufacturer's tabulated data cannot be utilized, designs shall be in accordance with appendix D.

Employees exposed to potential cave-ins must be protected by sloping or benching the sides of the excavation, by supporting the sides of the excavation, or by placing a shield between the side of the excavation and the work area.

OSHA CFR 1926 Subpart P Appendix D Aluminum Hydraulic Shoring for Trenches contains information that can be used when aluminum hydraulic shoring is provided as a method of protection against cave-ins in trenches that are not more than 20 feet deep.

This worker is in a trench with no protective system that is neither sloped nor benched and has no means of egress.

Reference 1926.652(a) and (b) and (c)

 

OSHA CFR 1926.652(c)

The project manager or his/her designee must select and construct designs of support systems, shield systems, and other protective systems

Trenches more than 5 feet deep must have proper shoring or must have a stabilized slope

Trenches less than 5 feet - a competent person must inspect to determine that a protective system is not necessary in soils where there is no indication of a potential cave-in

In hazardous soil conditions, trenches under 5 feet need protection

Factors Involved:

• Soil classification
• Depth of cut
• Water content of soil
• Changes due to weather and climate
• Other operations in the vicinity

General

•  Provides a framework to work in
•  Uses wales, cross braces and uprights
•  Supports excavation walls

OSHA tables provide shoring data. The competent person:

•  Must know soil type
•  Must know depth and width of excavation
•  Must be familiar with the OSHA Tables

A trench shield (also called a trench box) was built around this work area.  The individual working within this trench is now considered protected against ground cave-ins.

 

• 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; these keep the jacks in place

Reference 1926.652 (d)

(1)Materials and equipment used for protective systems shall be free from damage or defects that might impair their proper function.

(2)Manufactured materials and equipment used for protective systems shall be used and maintained in a manner that is consistent with the recommendations of the manufacturer, and in a manner that will prevent employee exposure to hazards.

(3)When material or equipment that is used for protective systems is damaged, a competent person shall examine the material or equipment and evaluate its suitability for continued use. If the competent person cannot assure the material or equipment is able to support the intended loads or is otherwise suitable for safe use, then such material or equipment shall be removed from service and shall be evaluated and approved by a registered professional engineer before being returned to service.

• Equipment used for protective systems must not have damage or defects that impair function.
• If the 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.

Reference 1926.651(f) Warning system for mobile equipment

When mobile equipment is operated adjacent to an excavation, or when such equipment is required to approach the edge of an excavation, and the operator does not have a clear and direct view of the edge of the excavation, a warning system shall be utilized such as barricades, hand or mechanical signals, or stop logs. If possible, the grade should be away from the excavation.

• Install barricades
• Hand/mechanical signals
• Stop logs
• Grade soil away from the excavation
• Fence or barricade trenches left overnight

In addition to the unprotected trench, a cave-in hazard is increased by machinery which gets too close.

Even normal vehicular traffic, such as that along an adjacent interstate or road through an industrial park may impact an excavation.  The vibrations from continuous or heavy traffic may undermine the soil and cause a cave-in.

• The weight and vibrations of the crane make this a very hazardous condition.
• They should not be working under this crane.

Reference 1926.651(j)(2)

Protect employees from materials or equipment that could fall or roll into excavations. 

You may also use retaining devices that are sufficient to prevent materials or equipment from falling or rolling into excavations

• Don’t place spoils within  2 feet from the edge of excavation
• Measure from the 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

Other excavation hazards may result due to:

 

• Water accumulation
• Oxygen deficiency
• Mobile Equipment
• Access/Egress
• Toxic Fumes
• Falls

When water is present in an excavation it is extremely hazardous to enter.

OSHA CFR 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.

(2)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.

(3)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.

The presence of water in an excavation should always be suspect. Not only may it erode side walls but the presence of water in the soil will

increase the weight per cubic foot of soil which, in itself, may cause a cave-in of side walls.

Excavations at a depth of 4' feet or greater must be tested for the following before human entry: 

• Oxygen deficiency
• High combustible  gas concentration
• High levels of other hazardous substances

The Competent Person 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 site management must also 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 a hazardous substance that exceed those specified in the Threshold Limit Values for airborne contaminants established by the ACGIH.

A stairway, ladder, or ramp must be present in excavations that are 4 or more feet deep, and within 25 feet of employees

Reference 1926.651(c(1)

Means of Egress (Structural ramps):

• Structural ramps that are used solely by employees as a means of access or egress from excavations shall be designed by a competent person. 
• Structural ramps used for access or egress of equipment shall be designed by a competent person qualified in structural design and shall be constructed in accordance with the design.
• Ramps and runways constructed of two or more structural members shall have the structural members connected together to prevent displacement.
• Structural members used for ramps and runways shall be of uniform thickness.
• Cleats or other appropriate means used to connect runway structural members shall be attached to the bottom of the runway or shall be attached in a manner to prevent tripping.
• Structural ramps used in lieu of steps shall be provided with cleats or other surface treatments to the top surface to prevent slipping.

Reference 1926.651(c) and 1926.1053 (ladder)

These two ladders which are lashed together are not an adequate means of egress.

The ladder should extend 3 feet above the top of the excavation.

Special Protection from Falls, Falling Loads and Mobile Equipment.

To protect employees from these hazards, OSHA requires the the following precautions:

• Keep materials or equipment that might fall or roll into an excavation at least 2 feet from the edge of excavations, or have retaining devices, or both.
• Provide warning systems such as mobile equipment, barricades, hand or mechanical signals, or stop logs, to alert operators of the edge of an excavation.  If possible, keep the grade away from the excavation.
• Provide scaling to remove loose rock or soil or install protective barricades and other equivalent protection to protect employees against falling rock, soil, or materials.
• Prohibit employees from working on faces of sloped or benched excavations at levels above other employees unless employees at lower levels are adequately protected from the hazard of falling, rolling, or sliding material or equipment.
• Prohibit employees under loads that are handled by lifting or digging equipment.  To avoid being struck by any spillage or falling materials, require employees to stand away from vehicles being loaded or unloaded.  If cabs of vehicles provide adequate protection from falling loads during loading and unloading operations, the operators may remain in them.
• Install barricades
• Use hand/mechanical signals
• Grade soil away from the excavation
• Fence or barricade trenches left overnight
• Use a flagger when signs, signals, and barricades are not enough protection

Reference 1926.651(k)

Daily inspections of excavations, the adjacent areas, and protective systems shall be made by a competent person for evidence of a situation that could result in possible cave-ins, indications of failure of protective systems, hazardous atmospheres, or other hazardous conditions.  An inspection shall be conducted by the competent person prior to the start of work and as needed throughout the shift. Inspections shall also be made after every rainstorm or other hazard increasing occurrence. These inspections are only required when employee exposure can be reasonably anticipated.

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 occurrences which may increase hazards, and
• When you can reasonably anticipate an employee will be exposed to hazards.

Reference 1926.651(k)

Where the competent person finds evidence of a situation that could result in a possible cave-in, indications of failure of protective systems, hazardous atmospheres, or other hazardous conditions, exposed employees shall be removed from the hazardous area until the necessary precautions have been taken to ensure their safety.

The following concerns must be addressed by the Competent Person:

 

• Evaluate soil conditions [1926 Subpart P Appendix A] and select appropriate protective systems [1926 Subpart P Appendix F]. 
• Construct protective systems in accordance with the standard requirements [1926.652].
• Preplan; contact utilities (gas, electric) to locate underground lines, plan for traffic control if necessary, determine proximity to structures that could affect the choice of the protective system.  
• Test for low oxygen, hazardous fumes, and toxic gases, especially when gasoline engine-driven equipment is running, or the dirt has been contaminated by leaking lines or storage tanks.
• Ensure adequate ventilation or respiratory protection if necessary.
• Provide safe access into and out of the excavation.
• Provide appropriate protections if water accumulation is a problem.
• Inspect the site daily at the start of each shift, following a rainstorm or after any other hazard-increasing event.
• Keep excavations open the minimum amount of time needed to complete operations. 
   
• Surface crossing of trenches should not be made unless absolutely necessary.  However, if necessary, they are only permitted under the following conditions:
• Vehicle crossings must be designed by and installed under the supervision of a registered professional engineer.
• Walkways or bridges must:
  • Have a minimum clear width of 20 inches,
  • Be fitted with standard rails, and
  • Extend a minimum of 24 inches past the surface edge of the trench.

•  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.