Chapter 11 Flashcards
In the U.S., an average of 60 to 100 workers die each year in trench cave ins.
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Before any trench rescue or entry operations are initiated, the area around the trench opening must be evaluated for stability.
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A shoring team is assigned the function of measuring and placing shoring members in the trench environment.
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Trench lip - top edge of a trench.
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Cut team - a team assigned the function of building shoring and cribbing elements and other items as needed.
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Shoring teams create a safe working environment by strategically placing components in a trench environment.
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Cut stations use powered and hand tools to build lumber components needed to support a trench rescue.
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Trenching tools include short handled shovels with a blade that can be swiveled 90 degrees to form a hoe.
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Collapsible canvas buckets are used to remove dirt from trenches during rescue operations.
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Vacuum trucks provide a means of quickly removing loose soil from the bottom of the trench.
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Generally, protective equipment is disassembled in the reverse order of placement.
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A trench should be considered an attractive nuisance and may make a tempting location for children to explore, or it might draw curious onlookers.
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According to NFPA 1006, the skill set of a Level 1 rescuer is limited to conducting trench rescue operations to a non-intersecting trench that is no deeper than 8 feet.
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Section 650 of 29 CFR 1926 defines the term trench at the US federal level as a narrow excavation made below the surface of the ground.
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In general, the depth is greater than the width, but the width of a trench is not greater than 15 feet.
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Trenches may be excavated in many different configurations including, straight wall, T, L, and X.
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A registered professional engineer must design shoring plans for trenches deeper than 20 feet.
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Soil is divided rock composed of natural mineral materials present in the earth’s crust.
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Sedimentary rock is composed of layers that include natural fissures between the layers.
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Trench lip protection should include indications of unstable areas.
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Cohesive soils get their strength through the friction and chemical bonding that occurs between particles.
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Cemented soils can lose stability through fissuring, and water can dissolve the minerals that bond the soil.
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Composed primarily of clay, cohesive soils vary based on the type of clay, the moisture content, and the amount of granular soil in the mixture.
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Granular soils are characteristically grainy and, depending on the size of particles, may be identified as gravel, sand, or silt.
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The stability of granular soils is dependent upon the angularity of the grains, the amount of natural cements present, and the moisture content.
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Loams are mixtures of cohesive soils and granular soils.
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The stability of loams depends on the percentage of each of the constituents and the moisture content.
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Cohesive soils may not be vary stable, depending on the moisture content of the soil and other environmental conditions.
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To simplify the field classification of soils, regulatory agencies in the US classify soils into four general types - stable rock, A, B, C.
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Depending upon its composition and moisture content, a cubic yard of soil can easily weigh over a ton.
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Testing soil samples from the spoil pile is an effective method of determining the condition of the soil in the trench walls.
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Cohesiveness is a factor of grain size.
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Cohesive soils remain in clumps, granular materials break up easily.
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Tension cracks and evidence of material spalling off the vertical trench walls could be indication of dangerously unstable soil.
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Evidence of layering in trench walls may show a slope toward the trench.
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