Presentation on theme: "EXCAVATION AND TRENCH PROTECTION"— Presentation transcript:
1 EXCAVATION AND TRENCH PROTECTION DANGERDeep ExcavationIS YOUR TEAM WORKING IN OR AROUND EXCAVATIONS. UNSTABLE EXCAVATIONS AND TRENCH WALLS CAN COLLAPSE, CRUSHING OR TRAPPING WORKERS. DEEP EXCAVATIONS CAN CAUSE SERIOUS INJURY OR DEATH IF A PERSON FALLS INTO THEM. LEARN HOW TO RECOGNISE DANGER AND PROTECT YOURSELF AND YOUR WORKMATES? READ THE INFORMATION BELOW AND DECIDE WHAT CHANGES CAN BE MADE TO THE WAY YOU WORK AND YOUR WORKING ENVIRONMENT TO MAKE IT A SAFER PLACETEST YOURSELF1. Describe two signs of soil distress:2. Describe why a worker buried up to the neck would not be able to breathe: ___________________________3. When working in a 4 ft (1.2m) trench, there must be an exit within 25 feet (8m). True or False? ______________________________4. Shielding is designed to prevent an excavated wall from caving in. True or False ?______________________________5. Name a portable device used for shielding: ______________________________6. How does water or rain impact the classification of soil?7. Trenches near landfills may not contain enough oxygen to support life. True or False? ___________________________8. Describe a way to protect trench workers from falling soil or objects: ___________________________9. Excavations need to be inspected only after they are first dug. True or False___________________________10. If you don’t know the soil type, what slope angle should you use to be safe? _____________Answers1. Signs of soil distress include cracks, slumping, bulging, sinking edge, or trickling pebbles.2. The soil exerts great pressure on the chest, which prevents chest expansion.3. True.4. False. Shoring prevent cave-ins and shielding protects workers from a cave-in.5. A trench box is a portable device that is used for shielding.6. Rain or water decreases the stability of soil. Saturated soil can be very unstable.7. True. The trench might be filled with a heavy gas (from the landfill) that displaces oxygen.8. Remove loose soil by scaling, provide protective barriers, keep material 2 feet (0.60cm) from trench’s edge.9. False. Inspect excavations daily, throughout the shift, and after conditions change./2 feet (0.45cm) horizontal for every vertical foot. So a 10 foot (3.1m) deep trench would slope out 15 feet (5m).What is a Trench?A narrow excavation deeper than it is wideNo more than 15 feet (5m) wide at bottomWhat is a cave-in?Soil or rock that suddenly falls or slides into an excavationCan entrap, bury, injure or immobilizeSoil gravitates downward, pressure pushes soil inward toward the trenchBottom third of wall typically fails firstSoil above the collapsed lower wall followsTrench BoxesOften designed to stackNever use sheeting to extend the heightCan be used in conjunction with sloping and benchingNo one permitted inside when being raised or loweredExcavations and InspectionsInspections conducted before work starts, throughout shifts and after rainstorm or snow/ice thawExcavations inspected for:Evidence of possible cave-insIndications of failure of protective systemsPotential hazardous atmosphereIf hazardous conditions are found, workers are not permitted to workSigns of Soil DistressFissures or cracksSlumping of materialBulging or heaving of material at the bottom lSinking of excavation’s edgeRavelling, or small amounts of material (i.e., pebbles) trickling into excavationConditions Causing Soil DistressNearby vibrating machineryNearby heavy, moving loadsSeeping water or rainHot, dry weatherFreeze and thawing of soilSupervisor and Safety Advisor carry out hazardous atmosphere checks prior to any work starting. A trained watchman stands by.Falling Soil or EquipmentProtect workers from loose rock/soil that may fall from an excavation faceCarry out scaling to remove loose soilInstall protective barricades, such as shoring or shieldsProtect workers from material or equipment that could fall into the excavationKeep material/equipment 2 feet (0.6m) from edgeUse retaining devicesAdjacent StructuresExcavations might endanger stability of buildings, walls, other structuresSidewalks, pavement not to be undermined unless supported to prevent collapseShoring, bracing, or underpinning used to ensure stability for employee protectionWater AccumulationWorkers have drowned in the water at the bottom of a trench or excavationNever work in an excavation where water is accumulating without proper precautionsSpecial shoring or shield systemWater removal system in operationPlace barriers and warning signs around deep excavations.Sloping trench walls is carried out mechanically, while supervisors check the installation of trench protection and look for potential hazards prior to work startingHazardous AtmospheresExcavations near sewers, landfills, hazardous substances storage areas may contain gassesTest atmosphere when deeper than 4 feet (1.3m)Ventilation or appropriate PPERescue and emergency equipment readyOther Trenching IssuesMark underground utilitiesStand away from lifting/digging equipmentUse warning systems or barricadesAlways use the correct PPETrenches 4 feet deep or more must have exit means within 25 feet of every workerUse fall protectionWorker on top watches excavation walls to warn trench workers of potential hazardsRememberCave-ins occur suddenly and can entrap, bury, or injureSoils have varying stability that determines the appropriate protectionBe aware of signs of soil distressBe aware of hazards associated with working around excavationsCarry out JSA before you start workSloping and BenchingSloping: this means angling of walls at an incline to help stabilize the slopeBenching: cutting a series of steps to angle the wallsSoil type determines angle of slope / benchType A: 3 feet (1.0m) horizontal to 4 feet 1.3m vertical (3/4:1)Type B: 4 feet (1.3m) horizontal to 4 feet (1.3m) vertical (1:1)Type C: 6 feet (1.8m) horizontal to 4 feet (1.3m) vertical (1-1/2:1)Benching is not permitted for Type C soilShoringSupport walls designed to prevent cave-inUsually built in place and designed by an engineerComponents include: uprights (sheeting), wales, and cross bracesShieldingWithstands forces of a cave-in and protects employees withinPermanent or portableTrench boxesDepending on soil stability it may not be necessary to slope trench walls. Required slope must be determined by a qualified engineer.Cave-in InjuriesSoil weighs 125 lbs per cubic foot or 170kgs per cubic meter.A worker can be crushed by soil, rock, or an objectSuffocation can occur even if worker’s head is not buried, soil exerts great pressure and prevents chest expansionImmobilized by soil’s suction effectSoil Classification is determined byGrain sizeSaturationCohesivenessUnconfined compressive strengthKnow Soil TypesType A - dense and heavy clay (most stable)Type B - silt, sandy loam, medium clayType C - gravel, loamy sand, soft clay (least stable)Purpose designed trench protection boxes must be used in unstable soils. Ensure they are used, protect yourselfWorking alone in a trench without supervision is dangerous and NOT permitted!Do not work on sides of sloped or benched excavation above other workersPrepared by: Andy Britten December 03
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