Excavations : OSHA Office of Training and Education 1 Excavations
Excavation Hazards : OSHA Office of Training and Education 2 Excavation Hazards Cave-ins are the greatest risk
Other hazards include:
Asphyxiation due to lack of oxygen
Inhalation of toxic materials
Fire
Moving machinery near the edge of the excavation can cause a collapse
Accidental severing of underground utility lines
Injury and Death : OSHA Office of Training and Education 3 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 : OSHA Office of Training and Education 4 Definitions Excavation – a man-made cut, cavity, trench, or depression formed by earth removal 15 ft and wider.
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.
Slide 5 : OSHA Office of Training and Education 5 Focus of Training The greatest risk at an excavation
How to protect employees from cave-ins
Factors that pose a hazard to employees working in excavations
The role of a competent person at an excavation site
Protection of Employees : OSHA Office of Training and Education 6 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 : OSHA Office of Training and Education 7 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 : OSHA Office of Training and Education 8 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
The three S’s are as follows
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 : OSHA Office of Training and Education 9 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
Slope Angels : OSHA Office of Training and Education 10 Slope Angels Type A = ¾-1
Type B = 1-1
Type C = 1 ½- 1
First # = horizontal
Second # = vertical
Slide 11 : OSHA Office of Training and Education 11 Cave-in Hazard This excavation has inadequate support posts and egress access Inadequate protective system
Inadequate Protective System : OSHA Office of Training and Education 12 Inadequate Protective System
Factors Involved in Designing a Protective System : OSHA Office of Training and Education 13 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
Type A : OSHA Office of Training and Education 14 Type A Fine grained
Doesn’t crumble
Hard to break up when dry
Examples:
Clay
Hardpan
Silty or sandy clay, clay loam
Type B : OSHA Office of Training and Education 15 Type B Granular: coarse grains
Little or no clay content
Crumbles easily when dry
Examples:
Silt
Loam
Angular gravel
Type C : OSHA Office of Training and Education 16 Type C Granular soil very coarse
Minimal cohesion
Examples:
Sand
Gravel
Loamy sand
Wet soil
Unstable wet rock
Shoring : OSHA Office of Training and Education 17 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
Slide 18 : OSHA Office of Training and Education 18
Trench Shield : OSHA Office of Training and Education 19 Trench Shield A trench shield was built around this work area
Shield : OSHA Office of Training and Education 20 Shield Shields are manufactured by a number of companies and are designed to protect workers working within the confines of the shield.
Tabulated data for the maximum allowable depth it can be used. The tabulated data must accompany the shield when it is being used.
Additionally, the shield must be designed by a Registered Professional Engineer, be in good condition, and used properly.
Hydraulic Trench Support : OSHA Office of Training and Education 21 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 : OSHA Office of Training and Education 22 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 : OSHA Office of Training and Education 23 Protection from Vehicles Install barricades
Hand/mechanical signals
Stop logs
Grade soil away from excavation
Fence or barricade trenches left overnight
Slide 24 : OSHA Office of Training and Education 24
Slide 25 : OSHA Office of Training and Education 25 Hazardous Conditions The weight and vibrations of the crane make this a very hazardous condition.
They should not be working under this crane.
Spoils : OSHA Office of Training and Education 26 Spoils Don’t place spoils within 2 feet from edge of excavation
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
Slide 27 : OSHA Office of Training and Education 27 Other Excavation Hazards Water accumulation
Oxygen deficiency
Toxic fumes
Access/Egress
Falls
Mobile equipment
Water is Hazardous : OSHA Office of Training and Education 28 Water is Hazardous When water is present in an excavation it is extremely hazardous to enter Note that these workers are not wearing hardhats to protect them from materials falling into the trench
Help! : OSHA Office of Training and Education 29 Help!
Water = Cave-in Hazard : OSHA Office of Training and Education 30 Water = Cave-in Hazard These workers must be protected from cave-in. Note the water in the bottom of the trench. This is a very hazardous condition!
Hazardous Atmosphere : OSHA Office of Training and Education 31 Hazardous Atmosphere Test excavations more than 4 feet before an employee enters the excavation for:
Oxygen deficiency
High combustible gas concentration
High levels of other hazardous substances
Means of Egress : OSHA Office of Training and Education 32 Means of Egress A stairway, ladder, or ramp must be present in excavations that are 4 or more feet deep, every 25 feet laterally This ladder does not meet the requirements of the standard The ladder should extend 3 feet
above the excavation
Slide 33 : OSHA Office of Training and Education 33 Access and Egress 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
Protection from Falls, Falling Loads, and Mobile Equipment : OSHA Office of Training and Education 34 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
Slide 35 : OSHA Office of Training and Education 35 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 : OSHA Office of Training and Education 36 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 : OSHA Office of Training and Education 37 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 : OSHA Office of Training and Education 38 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 Fissure
Slide 39 : OSHA Office of Training and Education 39 Summary 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.