4 of 34

Excavation Hazards

Excavation 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 breaking of underground utility lines

5 of 34

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 4 meters
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.

6 of 34

The risk of working in excavation

How to protect employees from cave-ins

Factors that pose a hazard to employees working in excavations

The role of a competent person in excavation site

Focus of Training

7 of 34

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

8 of 34

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

9 of 34

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

10 of 34

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

11 of 34

Cave-in Hazard

This excavation has inadequate support posts and egress & access

Inadequate protective system

12 of 34

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

13 of 34

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

14 of 34

Shoring

General

Provides a framework to work in
Uses wales, cross braces and uprights
Supports excavation walls
Must know soil type
Must know depth and width of excavation

15 of 34

Sloping & Benching

The design of protection systems, including sloping, benching, shoring and shielding, will depend primarily on two factors:

The types of soil encountered, and in the depth of the excavations
Persons working in excavations can be protected by sloping and benching the sides of the excavation in accordance with the industrial safety and Health Law

16 of 34

Sloping & Benching

	Type	Slope	maximum degree
Soil	Wet soil	1 : 1 ~ 1 : 1.5	45° ~ 34°
	Dry soil	1 : 0.5 ~ 1 : 1	63° ~ 45°
Rock	Weathered rock	1 : 0.8	51°
	Loose rock	1 : 0.5	63°
	Stable rock	1 : 0.3	73°

17 of 34

Trench Shield

A trench shield was built around this work area

18 of 34

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

19 of 34

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.

20 of 34

Protection from Vehicles

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

21 of 34

Hazardous Conditions

The weight and vibrations of the crane make this a very hazardous condition.

They should not be working under this crane.

22 of 34

Spoils

Don’t place spoil soil within 1 meter from edge of excavation
Rocks, stones or other debris will not be left any closer than 2 meters to the edge of the 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

23 of 34

Water accumulation

Oxygen deficiency

Toxic fumes

Access/Egress

Falls

Mobile equipment

Other Excavation Hazards

24 of 34

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

25 of 34

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!

26 of 34

Hazardous Atmosphere

Test excavations more than before an employee enters the excavation for:

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

27 of 34

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

This ladder does not meet the requirements of the standard

The ladder should extend 3 feet

above the excavation

28 of 34

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

Hanging electrical cables touching the aluminum ladder

Access and Egress

29 of 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 flag man when signs, signals and barricades are not enough protection
All heavy equipments (e.g. compressor units, generators, etc.) shall be kept minimum of 2 meters away from the edge
Wheel locks are to be placed on any wheeled vehicle, which is parked, in close proximity to an excavation.
Heavy vehicular traffic shall not be permitted near un-shored sides
Location of underground utilities

30 of 34

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

31 of 34

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.

32 of 34

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

33 of 34

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

34 of 34

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.

Summary