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TRENCH AND EXCAVATION SAFETY GUIDE

I. POLICY A. PURPOSE The purpose of the Excavation and Trenching Safety Program is to put into place work

practices and procedures that will protect workers from the hazards that may be found in or around excavations or trenches.

B. DUTIES AND RESPONSIBILITIES

1. Designated Supervisors shall:

a. Work with the Safety Supervisor and Engineer in preparing and implementing all

provisions of the Trenching and Shoring Plan for work areas under their control; b. Receive training for “Competent Person” for trenching as defined by Cal/OSHA. c. Act as the “Competent Person” for excavation sites under their control; d. Assure that the equipment necessary to complete an excavation safely is

available and in good condition; e. Assure that all underground utility installations such as sewer, telephone, fuel

tanks, electric, gas, and water lines are located and marked before excavation begins;

f. Conduct soils tests to determine soil type; g. Ensure that underground installations are protected, supported or removed while

the excavation is open; h. Ensure worker protection and compliance with other applicable safety plans,

programs and guidelines; i. Ensure protection of the public with appropriate barricades; j. Determine what protective systems will be used to prevent cave-ins; and, k. Conduct daily inspections of excavations, the adjacent areas, and protective

systems for evidence of a situation that could result in possible cave-ins, indications of failure of protective systems, hazardous atmospheres or other hazardous conditions.

2. Employees shall:

a. Complete all safety training requirements and request further instruction if

unclear on any part of the Trenching and Shoring Plan;

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b. Use appropriate safety and personal protective equipment (PPE); c. Adhere to the requirements of the Trenching and Shoring Plan; and, d. Report all work place injuries and unsafe conditions.

3. Safety Supervisor a. Provide consultation b. Work with the designated Supervisor/Competent person or Engineer in preparing

the Trenching and Shoring Plan with periodic review and revisions as needed; c. Distribute the Trenching and Shoring Plan to all affected individuals; d. Investigate and document all reported accidents and/or near-miss accidents that

are directly or indirectly related to trenching; and receive training as” Competent Person” to assist the designated Supervisor in developing the Trenching and Shoring Plan.

e. Coordinate training and retraining of those who may be involved in excavations.

II. TRAINING

All personnel involved in trenching or excavation work shall be trained in the requirements of this plan. Training shall be performed before anyone is assigned duties in excavations.

A. TRAINING OF THE DESIGNATED SUPERVISOR

1. All Designated Supervisors of trenches and excavations shall meet the Cal/OSHA

requirements for a “Competent Person.” 2. Designated Supervisors will attend a “Competent Person” training course.

B. TRAINING OF WORKERS

Personnel who perform work in excavations shall comply with the requirements of this plan

and receive appropriate training that shall include at a minimum: 1. Safe work practices that must be followed during work in excavations.

2. The use of personal protective equipment (PPE) that will typically be required during

work in excavations, including but not limited to safety shoes, hardhats, and fall protection devices;

3. Procedures to be followed if a hazardous atmosphere exists or could reasonably be

expected to develop during work in an excavation; and 4. Emergency and non-entry rescue methods, and procedures for calling rescue

services.

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C. RETRAINING

Retraining will be performed whenever site inspections conducted by the Designated Supervisor or the Safety Office indicate that a worker does not have the necessary knowledge or skills to safely work in or around excavations.

III. EXCAVATION PROCEDURES A. PRE-WORK SITE INSPECTION

Prior to excavation the site shall be thoroughly inspected by the Designated Supervisor to

determine if special safety measures must be taken. (See Appendix A.)

B. SURFACE ENCUMBRANCES All equipment, materials, supplies, permanent installations (for example, buildings or

roadways), trees, brush, boulders, and other objects at the surface that could present a hazard to employees working in the excavation shall be removed or supported as necessary to protect employees.

C. UNDERGROUND UTILITIES

1. The location of sewers, telephone, fuel, electric, water lines, or other underground installations that may be encountered during excavation work shall be determined and marked prior to opening an excavation.

2. The Underground Service Alert (Dig Alert) will be contacted to request marking of all

existing underground utilities. (Call 811 – Toll Free.) See Appendix B. 3. If the nature of the emergency requires the initiation of the excavation prior to the

placement of utility location markings, all excavation shall be done with the assumption that other utilities exist in the area.

4. Utilities left in place shall be protected by barricades, shoring, suspension or other

means as necessary to protect employees. 5. When constructing substructures around an existing duct line, the cables and/or duct

lines containing cables shall be properly supported and protected from physical damage.

6. Movement and rerouting of cables shall be done by qualified workers.

D. CHIPPING CONCRETE

1. Personal protective devices such as goggles, protective face shields with eye protection, foot shields, and hearing protection shall be worn when appropriate for the chipping operations.

2. Caution shall be exercised not to strike electric or telephone conduits, gas lines or

other substructures when working in tunnels or trenches.

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3. When chipping around a duct line containing energized high-voltage conductors (600 volts and above), an “OK – TO WORK HOT” shall be obtained and a second qualified person shall be present and shall act as a safety observer.

4. Exercise extreme caution while exposing duct. Consider that all conduits contain

energized cables until proven otherwise. 5. Cables adjacent to a chipping operation shall be de-energized when possible and

protected, as the hazard requires. 6. Consult the Electrical Services Section Rule No.6 (Chapter 44) for more guidelines

on conduit chipping procedure, when working on electrical services projects.

E. ADJACENT STRUCTURES Excavations adjacent to buildings, walls, or other structures shall not commence until support for such facilities has been provided. If the ability of the side slopes of the excavation to support such structures is in question, the excavation shall not proceed until a registered professional engineer has determined that the excavation will not pose a hazard to the workers or to the stability of the structure.

F. PROTECTION OF THE PUBLIC

1. Barricades, walkways, lighting and posting shall be provided as necessary for the protection of the public prior to the start of excavation procedures.

2. Guardrails, fences, or barricades shall be provided on excavations adjacent to

walkways, driveways and other pedestrian or vehicle thoroughfares. Warning lights or other illumination shall be maintained as necessary for the safety of the public and employees from sunset to sunrise.

G. SURFACE CROSSINGS

Surface crossing of trenches should be discouraged; however, if trenches must be crossed, such crossings are permitted only under the following conditions:

1. Vehicle crossings must be designed by and installed under the supervision of a registered professional engineer.

2. Walkways or bridges must be provided for foot traffic. These structures shall:

a. have a safety factor of 4; b. have a minimum clear width of 20 in (0.51 m); c. be fitted with standard rails; and d. extend a minimum of 24 in (.61 m) past the surface edge of the trench.

H PROTECTION OF WORKERS IN EXCAVATIONS

1. Access and Egress a. Stairs, ladders or ramps shall be provided where workers are required to enter

trench excavations over 4 feet deep. b. A means of exit shall be provided every 25 feet of trench length.

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c. Ladders must be secured and extend a minimum of 36 inches above the landing. (See Chapter 33, Ladders, for general information and inspection requirements.)

I. VEHICULAR TRAFFIC

When the work area is in or adjacent to a vehicular right of way, all workers shall be

provided with and shall wear high visibility vests or other suitable garments. (See Chapter 37, Traffic Control.)

J. FALLING LOADS

1. Workers shall stand away from loading or unloading operations to avoid being struck

by spillage or falling materials. 2. No worker shall be permitted underneath loads being handled by lifting or digging

equipment.

K. SOIL FALL HAZARD

1. Workers doing work in an excavation shall be protected from falling rock or soil. 2. Side slopes of the excavation (trench) shall be scaled to remove loose material and

protective covering added as necessary to prevent material from falling. 3. Excavated spoil and equipment shall be placed at least two feet from the edge of

excavations and/or sufficiently restrained in order to prevent movement into the excavation.

L. WARNING SYSTEM FOR MOBILE EQUIPMENT

A warning system shall be used when mobile equipment is operated next to the edge of an

excavation if the operator does not have a clear, direct view of the edge of the excavation.

M. WORKING DISTANCE

1. A safe working distance shall be maintained from other workers to avoid being struck by their tools.

2. Workers shall not work where they are out of sight or more than 50’ from other

workers. 3. Workers shall not work closer than six feet to an excavating machine in

operation. The employee shall face the machine while working within 6 feet of equipment not in operation.

N. HAZARDOUS ATMOSPHERES

If the possibility of a hazardous atmosphere exists, excavation entrance shall not be authorized until testing (with corrective action taken if necessary) indicates that an acceptable atmospheric condition exists. The requirements for confined space atmospheric

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testing in Chapter 21- Confined Space Policy, shall be followed if a hazardous atmosphere is suspected. If a hazardous atmosphere occurs during excavation work (such as a gas leak), all workers shall evacuate the immediate area until the hazard is abated.

O. WATER ACCUMULATIOIN

Because of the necessity of dealing with leaking water pipelines, water accumulation is a frequent concern. All subsurface excavations where the soil is saturated, or there is standing water, shall include special precautions to protect against the hazards of soil slippage or cave-ins. Precautions or methods may consist of the following:

1. Use of special support or shield systems approved by a Registered Professional

Engineer. 2. Water removal equipment, such as pumps, used and monitored by a competent

person. 3. No one shall work in excavations during a rainstorm unless circumstances warrant it

and adequate precautions are taken. 4. Trenches shall be inspected by the Designated Supervisor after each rain and before

anyone is permitted to re-enter the excavation.

P. INSPECTIONS

1. The Designated Supervisor shall conduct daily inspections of excavations, adjacent area, and protective systems for evidence of a situation that could result in a cave-in, failure of protective systems, hazardous atmospheres, or other hazardous conditions.

2. Inspections should be conducted prior to the start of work and as needed throughout

the shift. 3. Inspections should also be made after every rainstorm. 4. These inspections are only required when the trench will be or is occupied by

workers. 5. When a hazardous condition is found, exposed workers shall be removed from the

area until precautions have been taken to assure their safety. 6. Inspections shall be documented on the Trench Inspection form. (See Appendix C)

IV. REQUIREMENTS FOR PROTECTIVE SYSTEMS A. PROTECTION OF WORKERS IN EXCAVATIONS Personnel working in an excavation shall be protected from cave-ins by using either an

adequate sloping and benching system or an adequate support or protective system. The only exceptions are when the excavation is made entirely in stable rock or the excavation is

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less than 5 feet in depth where examination of the ground by the Designated Supervisor provides no indication of a potential cave-in.

B. SOIL CLASSIFICATIONS

In order to design the most appropriate protective system, the Designated Supervisor shall

determine the soil type using a visual test or one or more manual tests. A soil analysis form shall be completed to document the results of the tests. (See Appendix A.) 1. Visual Test The entire excavation site including the soil adjacent to the site is observed. During

the visual test, the Designated Supervisor shall check for crack-line openings along the failure zone that indicate tension crack and observe the open side of the excavation for indications of layered geologic structuring. Other conditions to look for are signs of bulging, boiling or sloughing, as well as signs of surface water seeping from the side of the excavation or from the water table.

2. Manual Tests

a. Thumb Penetration Test – When the thumb is pressed firmly in to the soil and penetrates no further than the length of the nail, it is probably Type B soil. If the thumb penetrates the full length of the thumb, it is Type C. This is the least accurate of the manual test methods.

b. Dry Strength Test – If a sample of dry soil is crumbled freely or with moderate

pressure into individual grains it is considered granular, or Type C. Dry soil that falls into clumps that subsequently break into smaller clumps is probably clay in combination with gravel, sand, or silt (Type B).

c. Plasticity or Wet Thread Test – A moist sample of the soil is molded into a ball

then rolled into a thin thread approximately 1/8 inch in diameter by two inches in length. If the soil sample does not break when held by one end, it may be considered Type B. If the soil sample does break, it is considered Type C.

d. A pocket penetrometer, shear vane, or Tourane may also be used to determine

the unconfined compression strength of soils.

C. TYPES OF PROTECTIVE SYSTEMS

The following systems may be used to protect workers from cave-in in trenches of more than 5 feet deep. The Designated Supervisor should select the method of protection that is most suitable for the particular job site, taking into consideration soil type and surrounding structures. If the soil is not classified, then the excavation must be sloped at an angle not steeper than one and a half horizontal to one vertical. Protective systems for Excavation greater than 20 feet shall be approved by a registered Professional Engineer.

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1. Sloping Maximum allowable slopes for excavations less than 20 feet deep based on soil type

and angle to the horizontal are as follows:

A 10 foot deep trench in Type B soil would have to be sloped to a 45-degree angle,

or sloped 10-feet back in both directions. Total distance across a 10-foot-deep trench would be 20-feet, plus the width of the bottom of the trench itself. In Type C soil, the trench would be sloped at a 34-degree angle, or 15-feet back in both directions for at least 30-feet across, plus the width of the bottom of the trench itself. (Attachment B illustrates simple slope trenching in B and C type soils.)

2. Benching As a general rule, the bottom vertical height of the trench must not exceed 4 ft (1.2 m) for the first bench. Subsequent benches may be up to a maximum of 5 ft

(1.5 m) vertical in Type A soil and 4 ft (1.2 m) in Type B soil to a total trench depth of 20 ft (6.0 m). All subsequent benches must be below the maximum allowable slope for that soil type. For Type B soil, the trench excavation is permitted in cohesive soil only.

Benching is not permitted in Type C soil.

3. Shoring Shoring is used when the location of the trench makes sloping back to the maximum

allowable slope impractical. There are two basic types of shoring Timber and Aluminum hydraulic. a. Timber The Designated Supervisor should use the information in the tables of Title 8

CCR Section 1541.1 Appendix D – Timber Shoring for Trenches. The members

Table 1 – Allowable Slopes

Soil

type Height/Depth ratio Slope angle

Stable Rock Vertical 90°

Type A ¾:1 53°

Type B 1:1 45°

Type C 1½:1 34°

(For a maximum excavation depth of 12 ft)

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of the shoring system that are to be selected using the tables are the cross braces, the uprights, and the wales where wales are required. The Designated Supervisor shall select the size and spacing of members using the appropriate table. The selection is based on the depth and width of the trench where the members are to be installed. In most instances, the selection is also based on the horizontal spacing of the cross braces. Where a choice is available, the horizontal spacing of the cross braces must be chosen before the size of any member can be determined.

b. Hydraulic Aluminum Shoring

Hydraulic shoring provides a critical advantage over timber shoring because

workers do not have to enter the trench to install them. They are gauge-regulated to ensure even distribution of pressure along the trench line; and they can be adapted easily to various trench depths and widths.

Hydraulic Shoring Support Systems shall be constructed and used in accordance with all specifications, recommendations and limitations issued by the manufacturer.

4. Shielding Trench boxes are different from shoring because instead of shoring up or otherwise

supporting the trench face, they are intended primarily to protect workers from cave-ins. Trench boxes are generally used in open areas, but they may be used in combination with sloping and benching. The Designated Supervisor shall ensure that the following safety measures are taken: a. Trench boxes shall be inspected for good condition each use. b. The excavated area between the outside of the trench box and the face of the

trench should be minimized. The space between the trench box and the excavation side must be backfilled to prevent lateral movement of the box.

c. The trench box must extend at least 18 inches above the surrounding area if there is sloping toward the excavation. This can be accomplished by providing a sloped area adjacent to the box.

d. Shields may ride two feet above the bottom of the excavation provided they are calculated to support the full depth of the excavation and there is no caving under or behind the shield.

e. Any modification to the shields must be approved by the manufacturer. f. Workers must enter and leave the shield in a protected manner, such as by a

ladder. Workers may not remain in the shield while it is being moved. 5. Protective Methods Using Other Tabulated Data Other tabulated data, such as tables and charts, may be selected for the design of

sloping, benching, shoring, or shielding systems. The tabulated data used must be written and include the following:

a. Identification of the factors that affect the selection of a protective system; b. Identification of the limits of use of the data; c. Information needed by the user to make a correct selection of a protective

system for the data; and

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d. At least one copy of the tabulated data with identifies the Registered Professional Engineer who approved the data shall be maintained at the job site during construction of the protective system.

6. Design by a Registered Professional Engineer

Sloping, benching, shoring and shielding systems may be designed by a Registered

Professional Engineer. The design shall be written and shall include the following:

a. A plan indicating the sizes, types, and configurations of the materials to be used in the protective system.

b. The identity of the Registered Professional Engineer approving the design. c. At least one copy of the design shall be maintained at the job site during

construction of the protective system. NOTE: All excavations more than 20 feet in depth must be approved by a Registered Professional Engineer.

V. EMERGENCY RESCUE

In the event of any emergency situation requiring rescue from an excavation, City of Glendale personnel shall not attempt to enter an unprotected trench to perform rescue.

Rescue services that can be performed safely from outside the excavation, such as hoisting a

harnessed victim, shall be undertaken. Other personnel in the excavation shall exit immediately, providing assistance only when not endangering their own safety.

Emergency rescue services will be provided for all trench emergencies by City of Glendale’s Fire

Department and fire departments in other jurisdictions as needed for mutual aid.

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APPENDIX A

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APPENDIX A (CONT’D)

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APPENDIX A (CONT’D)

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APPENDIX B

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APPENDIX C

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APPENDIX D

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APPENDIX D

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APPENDIX D

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APPENDIX D

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APPENDIX D

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APPENDIX D