EXCAVATION AND TRENCH PROTECTION DANGER Deep Excavation IS 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 PLACE TEST YOURSELF 1. 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? _____________ Answers 1. 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. 10. 1-1/2 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 wide No more than 15 feet (5m) wide at bottom What is a cave-in? Soil or rock that suddenly falls or slides into an excavation Can entrap, bury, injure or immobilize Soil gravitates downward, pressure pushes soil inward toward the trench Bottom third of wall typically fails first Soil above the collapsed lower wall follows Trench Boxes Often designed to stack Never use sheeting to extend the height Can be used in conjunction with sloping and benching No one permitted inside when being raised or lowered Excavations and Inspections Inspections conducted before work starts, throughout shifts and after rainstorm or snow/ice thaw Excavations inspected for: Evidence of possible cave-ins Indications of failure of protective systems Potential hazardous atmosphere If hazardous conditions are found, workers are not permitted to work Signs of Soil Distress Fissures or cracks Slumping of material Bulging or heaving of material at the bottom l Sinking of excavation’s edge Ravelling, or small amounts of material (i.e., pebbles) trickling into excavation Conditions Causing Soil Distress Nearby vibrating machinery Nearby heavy, moving loads Seeping water or rain Hot, dry weather Freeze and thawing of soil Supervisor and Safety Advisor carry out hazardous atmosphere checks prior to any work starting. A trained watchman stands by. Falling Soil or Equipment Protect workers from loose rock/soil that may fall from an excavation face Carry out scaling to remove loose soil Install protective barricades, such as shoring or shields Protect workers from material or equipment that could fall into the excavation Keep material/equipment 2 feet (0.6m) from edge Use retaining devices Adjacent Structures Excavations might endanger stability of buildings, walls, other structures Sidewalks, pavement not to be undermined unless supported to prevent collapse Shoring, bracing, or underpinning used to ensure stability for employee protection Water Accumulation Workers have drowned in the water at the bottom of a trench or excavation Never work in an excavation where water is accumulating without proper precautions Special shoring or shield system Water removal system in operation Place 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 starting Hazardous Atmospheres Excavations near sewers, landfills, hazardous substances storage areas may contain gasses Test atmosphere when deeper than 4 feet (1.3m) Ventilation or appropriate PPE Rescue and emergency equipment ready Other Trenching Issues Mark underground utilities Stand away from lifting/digging equipment Use warning systems or barricades Always use the correct PPE Trenches 4 feet deep or more must have exit means within 25 feet of every worker Use fall protection Worker on top watches excavation walls to warn trench workers of potential hazards Remember Cave-ins occur suddenly and can entrap, bury, or injure Soils have varying stability that determines the appropriate protection Be aware of signs of soil distress Be aware of hazards associated with working around excavations Carry out JSA before you start work Sloping and Benching Sloping: this means angling of walls at an incline to help stabilize the slope Benching: cutting a series of steps to angle the walls Soil type determines angle of slope / bench Type 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 soil Shoring Support walls designed to prevent cave-in Usually built in place and designed by an engineer Components include: uprights (sheeting), wales, and cross braces Shielding Withstands forces of a cave-in and protects employees within Permanent or portable Trench boxes Depending on soil stability it may not be necessary to slope trench walls. Required slope must be determined by a qualified engineer. Cave-in Injuries Soil weighs 125 lbs per cubic foot or 170kgs per cubic meter. A worker can be crushed by soil, rock, or an object Suffocation can occur even if worker’s head is not buried, soil exerts great pressure and prevents chest expansion Immobilized by soil’s suction effect Soil Classification is determined by Grain size Saturation Cohesiveness Unconfined compressive strength Know Soil Types Type A - dense and heavy clay (most stable) Type B - silt, sandy loam, medium clay Type C - gravel, loamy sand, soft clay (least stable) Purpose designed trench protection boxes must be used in unstable soils. Ensure they are used, protect yourself Working alone in a trench without supervision is dangerous and NOT permitted! Do not work on sides of sloped or benched excavation above other workers Prepared by: Andy Britten December 03