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Excavation: Trenching Safety

​This Tailgate Talk is part of the NLTAPA collection.

Trench collapses cause dozens of fatalities and hundreds of injuries each year. Here are some guidelines that can help you trench safely on the work site.


  • Trenches 5 feet deep or greater require that a protective system be used.


  • Trenches 20 feet deep or greater require that a registered professional engineer design the protective system.


  • Keep heavy equipment and excavation spoils at least 2 feet away from the trench edge.


  • Provide stairways, ladders, ramps, or other safe means of access & egress in all trenches 4 feet or deeper every 25’. Consider this for shallower trenches as well!



Protective Systems


  • Sloping protects workers by cutting back the trench wall at an angle inclined away from the excavation.


  • Shoring protects workers by installing aluminum, hydraulic or other types of supports to prevent soil movement.


  • Shielding protects workers by using trench boxes or other types of supports to prevent soil cave-ins.



Competent Person


OSHA standards require that a competent person inspect the trench daily and as conditions change. (An OSHA “competent person” is defined as “one who is capable of identifying existing and predictable hazards in the surroundings or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them” [29 CFR 1926.32(f)].)



Four Types of Soil: (Quick Overview)


Stable Rock

Natural solid material that remains intact


Type A

Not previously disturbed cohesive soil with an unconfined compressive strength greater than or equal to 1.5 tsf


Type B

Unconfined compressive strength >0.5 tsf <1.5 tsf—angular gravel, silt, silt loam, sandy loam, and, in some cases, silty clay loam and sandy clay loam.


Type C

Unconfined compressive strength <0.5 tsf—Granular soils including gravel, sand, and loamy sand, soil from which water is freely seeping.



Configurations


Configurations of sloping and benching systems shall be in accordance with Figure B-1.



Resources and References:


OSHA 29 CFR 1926.32(f)

https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_ id=10618


OSHA Trenching and Excavating Webpage URL

https://www.osha.gov/SLTC/trenchingexcavation/index.html


American Pipeline Contractors Association Excavation and Trenching Best Practices http://www.americanpipeline.org/images/safetyzone/BestPractices/English/ ExcavAndTrenching_Operators.pdf