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Excavations

Module 13

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DISCLAIMERThis material was produced under grant

number SH-22248-1 from the Occupational Safety and Health Administration, U.S.

Department of Labor. It does not necessarily reflect the views or policies of

the U.S. Department of Labor, nor does mention of trade names, commercial

products, or organizations imply endorsement by the U.S. Government.

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Objectives• After this module you should be able to– identify the most common excavation

hazards– take the steps necessary to avoid those

hazards

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Excavation Facts• As many as 400 workers die and another 4000

injured as a result of cave-ins each year• Most deaths occur in trenches 5-14 feet deep• Cave-ins cause death by: suffocation, crushing,

loss of circulation, falling objects• 1 cubic foot of soil can weigh up to 140 lbs• 1 cubic yard of soil can weigh up to 3000 lbs

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Excavation Hazards• Cave-in of a trench• Contacting underground utilities• Getting struck by falling objects• Falling into an excavation• Hazardous atmospheres• Equipment rolling into excavations

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Competent Person• Every excavation job must have one• This person must be trained on and

knowledgeable in– soils classification– the use of protective systems– the requirements of the OSHA standards

• This person must be able to identify hazards and immediately eliminate them

• Enter excavations only after their approval

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this 6’ deep vertical-sided trench is dangerous because it is not protected

Corrective Actions: never enter a trench like this; notify your supervisor

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What is a Cave-In?A cave-in is the separation of a mass of soil

or rock material from the side of an excavation and its sudden movement into the excavation either by falling or sliding

that could entrap, bury, or otherwise injure and immobilize a worker.

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this worker is being exposed to a life threatening situation, an excavation with no cave-in protection

Corrective Action: never enter a trench unless it is less than 5’ deep and you get permission from your supervisor or it has cave-in protection

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Soil Types• Excavation rules differ depending on the

type of soil• A competent person must determine the

type of soil using at least one visual and one manual analysis

Soil Type Description

Stable Rock most stable

Type A stable soil

Type B disturbed soil

Type C loose soil

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Shielding

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The Theory of Shielding• Shielding does not actually prevent a

cave-in• Trench shields and boxes, if installed

correctly, are designed to protect workers from the forces of a cave-in

• In order for the shield to do its job, the worker must stay within the protection of the shield even when entering and exiting

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this trench is not shielded to the trench bottom properly; these workers are still at risk for a cave-in

Corrective Action: shield the trench to no more than 2’ from the bottom

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the same shield is missing struts/crossbraces

Corrective Action: always install manufactured shielding according to the manufacturer’s directions

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this incomplete installation provides little if any protection; in fact, the panels themselves can become a crushing hazard

Corrective Actions: always install manufactured cave-in protection according to the manufacture; never skip steps

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these workers have left the protection of their trench box; a cave-in could happen at any moment

Corrective Action: never work unprotected, cave-ins can happen anytime without warning

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Shoring

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The Theory of Shoring• Shoring prevents cave-ins• Shoring, if designed and installed

correctly, counteracts the force of a cave-in

• In order for the shoring to do its job, the worker must stay within the protection of the shoring even when entering and exiting the trench

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make-shift, improperly designed shoring does little other then provide a false sense of security

Corrective Action: manufactured shoring should be used; install the shoring according to the manufacturer

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Sloping and Benching

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The Theory of Sloping and Benching

• Sloping and benching prevents cave-ins• Sloping and benching, if done correctly,

removes the risk of cave-ins by widening the trench from the bottom up

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this worker is able to work without the fear of a cave-in

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this pipeline trench is benched to prevent cave-ins

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Ramps, Ladders, and Stairs

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the worker in this trench has no safe means of exit

Corrective Action: for trenches 4’ deep or greater, install a ramp, ladder, or stairs no less than every 25’ from a worker in the trench

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Additional Concerns• Underground utilities• Overhead hazards• Mobile equipment• Walkways• Water in excavations• Hazardous atmospheres

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striking underground utilities can be deadly

this worker has used the one-call system to locate utilities; also, he is using safe and acceptable means to find the exact location of the utility

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this worker is at risk of being struck by falling rocks and excavated materials, in particular this soil spoil is too close

Corrective Action: keep excavated material (spoil) at least 2’ from the edge of the excavation

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Corrective Action: keep tools materials and other project related items at least 2 feet from the edge

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when mobile equipment is operated adjacent to an excavation, the operator must have a clear and direct view of the edge of the excavation, or…

… a warning system shall be utilized such as barricades, stop logs, or hand or mechanical signals; if possible, the grade should be away from the excavation

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using this method to cross an excavation can result in a serious fall

Corrective Action: construct a proper and safe walkway

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walkways or bridges must have a safety factor of 4, have a minimum clear width of 20”, be fitted with standard rails, and extend a minimum of 24” past the surface edge of the trench

this is an example of a proper walkway

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the presence of water usually means soil that is unstable

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Corrective Actions: select, inspect, and use water removal equipment correctly; consider such things as air-quality and personal health issues

excavations must be kept as water free as possible

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with the water pump running, a possible carbon monoxide exposure now exists

excavations greater than 4 feet in depth must be evaluated for oxygen deficiency, flammability, and toxicity

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these workers installed a high exhaust pipe to prevent asphyxiation

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compressed gas cylinders are not to be brought into trenches

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trying to keep as many air contaminants as possible above grade is a good idea

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Applicable Standards• 1926 Subpart P Excavations

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Your Employer is Responsible For• Preplanning the work• Protecting you from cave-ins• Inspecting the excavation at least daily

and throughout the shift as needed• Taking prompt corrective action when

needed

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Your Employer is Responsible For• Making sure a ladder is within 25’ of your

work area when deeper than 4’• Ensuring that excavated dirt, rocks, and

other materials are kept back 2’ from the excavation’s edge

• Testing the air in areas suspect to atmospheric hazards

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You are Responsible For• Following you company’s excavation and

trenching safety rules• Never enter a vertical-sided trench unless

it is less then 5’ deep and you get permission from your supervisor

• Never enter a trench unless it is laid back, shielded, boxed, or in solid rock

• If a trench box is used, never leave its protection while in the trench

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Memory Check1. How many feet must the excavated soil,

your tools, and other supplies be kept back from the excavation’s edge?

a. 1 footb. 2 feetc. 7.5 feetd. 25 feet

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Memory Check2. At what depth must a ladder, ramp,

steps or runway be present for quick worker exit?

a. 4 feetb. 5 feetc. 10 feetd. it is never required

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Memory Check3. What is the greatest hazard facing a

worker while working in a trench?a. hazardous atmospheresb. fallsc. cave-insd. falling objects

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Memory Check4. Unless a competent person indicates

that there is a potential for a cave-in, at what depth is a protective system required for a trench?

a. 2 feetb. 4 feetc. 5 feetd. 10 feet