Keep Workers Safe While Trench Shoring By Steven Settelmayer Published On: Monday, April 27, 2015 7:58 PM

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Excavation and trenching is hazardous, so it is always important to practice safety. Without the proper precautions, workers can be badly hurt or even die due to dangerous exposures such as cave-ins, slipping and falling, structural failure and hazardous gases.

The following tips identify important elements to keep workers safe while trench shoring.

COMPETENT PERSON When inspecting a jobsite to determine where trenches will be, it is important to consider the many factors that come into play to provide the safest environment. Soil type, presence of ground water in the trench, surface encumbrances, location of existing structures and utilities (both underground and overhead) are but a few of the many things that must be taken into account to ensure worker safety. Per OSHA, it is also required to have a competent person, who is an individual responsible for monitoring worker safety on a jobsite. This person is required to be on all trench or excavation sites anytime there is potential employee exposure.

A competent person must be experienced in underground construction and trained in OSHA Subpart P. This requires attending an in-depth class that covers the trench and excavation standard, the intent and specifics of soil classification, and the specific characteristics and applications of how each of the systems work. This comprehensive class also should train employees on the potential risks on jobsites along with the responsibilities of the competent person. These risks include surface encumbrances, existing utilities, access and egress, exposure to vehicle hazards, falling loads, water accumulation, hazardous atmospheres, stability of adjacent structures, protection from loose soil or rocks, fall protection and required inspections.

SOIL TYPES A trench or excavation must have a protective system 5 feet or more in depth. Excavations less than 5 feet deep may still require a protective system if there is potential for cave-in. This call is the responsibility of the competent person. OSHA rules specify that a competent person on a jobsite will classify the soil type as Stable Rock, Type A, Type B or Type C in accordance with the definitions in 29 CFR 1926 Subpart P Appendix A. The competent person will classify the soil based on a visual and a manual test prescribed in Appendix A. It is also permissible to assume the soil is Type C and soil testing would not be required. When working in Type B soil, the protective systems minimum earthen slope is 1 horizontal to 1 vertical (45 degrees). The vertical height of benches in Type B soil cannot exceed 4 feet. When working in Type C soil, the protective systems minimum earthen slope is 1.5 horizontal to 1 vertical (34 degrees). The competent person is required to perform a daily inspection before prior to work and after each rainstorm or other hazard increasing occurrence.

Type A: o clay, silty clay and hardpan, which resist penetration. No soil is classified as Type A if it

is fissured, subject to vibration, was previously disturbed, is part of a sloped or layered system with a slope 4 horizontal to 1 vertical or greater or is seeping water.

Type B: o cohesive soil with an unconfined compressive strength greater than 0.5 tons per

square foot (TSF), but less than 1.5 TSF; o granular cohesionless soils, including angular gravel (similar to crushed rock), silt, silt

loam, sandy loam and, in some cases, silty clay loam and sandy clay loam; o previously disturbed soils, except those that would otherwise be classed as Type C

soil; and o soil that meets the unconfined compressive strength or cementation requirements for

Type A, but is fissured or subject to vibration. o dry rock that is not stable.

Type C: o soft cohesive soil with unconfined compression strength greater than 0.2 tons per

square foot, but less than 0.5 tons per square foot; o soft cohesive soil with unconfined compression strength less than 0.2 tons per square

foot; o clay, sand and loamy sand; o saturated soil that is stable, dry sand or dewatered soil; o fractured rock that is not stable; and o submerged sand and loamy sand that is flowing.

SELECTING A PROTECTIVE SYSTEM Sloping, shoring and trench shields are the three recognized types of protective systems. The decision on which one to use depends on the length, width and depth of the trench or pit and the lifting capability of onsite equipment. There are also several types of shoring systems, including timber, aluminum hydraulic shoring, beam and plate, soldier pile and lagging, tight sheeting and slide rail systems. Several types of trench shields, in varying heights, lengths and widths, are made of either aluminum or steel sidewalls. In some cases a site-specific engineered trench safety plan may be the best option and cost-effective solution for the job.

Soil is dynamic and, when opened for a pit or trench, can be dangerous. To keep workers safe, OSHA requires a competent person be on the jobsite to continuously monitor site conditions. There should be no short cuts when working in and around trenches or open pits as lives are in the balance. It is always best to consult with an experienced trench safety equipment supplier to determine which protective system will be best for the job.

Keep Workers Safe While Trench ShoringCOMPETENT PERSONSOIL TYPESSELECTING A PROTECTIVE SYSTEM