Presentation on theme: "Trenching and Shoring UNIVERSITY of N ORTHERN C OLORADO."— Presentation transcript:
Trenching and Shoring UNIVERSITY of N ORTHERN C OLORADO
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Injury and Death Excavating is one of the most hazardous construction operations Most accidents occur in trenches 5-15 feet deep There is usually no warning before a cave-in Trenching Related Deaths 2000 to 2006………..271 trenching fatalities
Rules Underground Utilities must be located and marked before excavations begin Employees are not allowed in the excavation while heavy equipment is digging All employees on an excavation site must wear hard hats Employees shall be removed from the trench during a rainstorm Do NOT work under raised loads Stand away from equipment that is being loaded or unloaded to avoid being struck by falling materials or spillage Trench that is 4 feet or greater in depth requires a trench inspection form filled out by the competent person. All excavations or trenches 4 feet or greater in depth shall be appropriately benched, shored, or sloped. Excavations or trenches 20 feet deep or greater must have a protective system designed by a registered engineer.
Inspection Form To be completed by Competent Person Review Form Turn completed forms into EHS.
Soil classification Type A Type A Fine grained Fine grained Doesn’t crumble Doesn’t crumble Hard to break up when dry Hard to break up when dry Type B Type B Granular: coarse grains Granular: coarse grains Little or no clay content Little or no clay content Crumbles easily when dry Crumbles easily when dry Clay Loam Clay Silty loam Loam Angular gravel
Soil Classification Type C Type C Granular soil: very coarse Granular soil: very coarse Minimal cohesion Minimal cohesion Examples: Examples: o Sand o Gravel o Loamy sand o Submerged soil or soil with freely seeping water o Submerged rock that is not stable. Sand Gravel Loamy sand
Definitions “Competent person” is someone who: Can identify existing or predictable hazards in an excavation Has authority to take corrective actions as necessary Is familiar with the DOSH excavation standards Is knowledgeable in soil analysis and classification as well as the erection, use, and precautions for the protective system on site
Definitions Excavation – a man-made cut, cavity, trench, or depression formed by earth removal. Trench – a narrow excavation. The depth is greater than the width, but not wider than 15 feet. Shield - a structure able to withstand a cave-in and protect employees Shoring - a structure that supports the sides of an excavation and protects against cave-ins Sloping - a technique that employs a specific angle of incline on the sides of the excavation. The angle varies based on assessment of impacting site factors. Cave-in – The separation of soil or rock material from the side of an excavation.
Design of Protective Systems The employer shall select and construct : slopes and configurations of sloping and benching systems support systems, shield systems, and other protective systems Shield - can be permanent or portable. Also known as trench box or trench shield. Shoring - such as metal hydraulic, mechanical or timber shoring system that supports the sides Sloping - form sides of an excavation that are inclined away from the excavation
Materials and Equipment Equipment used for protective systems must not have damage or defects that impair function. If equipment is damaged, the competent person must examine it to see if it is suitable for continued use. If not suitable, remove it from service until a professional engineer approves it for use.
Benching Benching can be used in conjunction with sloping. Benching is NOT allowed in Type C soil. The bottom vertical height of the trench must not exceed 4 feet. Benches must be below the maximum allowable slope for that soil type. (example: A 10-foot deep trench in Type B soil must be benched back 10 feet in each direction, with the maximum of a 45 degree angle.)
Sloping Maximum allowable slopes for excavations less than 20 feet based on soil type and angle to the horizontal are as follows: Soil TypeHeight/Depth RatioSlope Angle Type A¾ : 153 degrees Type B1 : 145 degrees ees Type C1½ : 134 degrees
Shoring A support system for trench faces used to prevent movement of soil, underground utilities, roadways, and foundations. Three types of shoring: Aluminum Hydraulic Timber Pneumatic
Shielding Shielding also known as Trench Boxes focus on protecting from cave-ins. Workers must enter and leave the shield in a protective manner (ladder or ramp) Workers may NOT remain in the shield while the shield is being moved.
Inadequate Protective System This excavation has inadequate support posts and egress access This worker is in a trench with no protective system, that is not sloped or benched and has no means of egress
Hazardous Conditions The weight and vibrations of the crane makes this a very hazardous condition. They should not be working under this crane.
Warning Systems The following steps should be taken to prevent vehicles or people from falling Barricades must be installed where necessary Hand or mechanical signals must be used as required Trenches left open overnight shall be fenced and barricaded
Ingress / Egress Access to and exit from the trench requires the following conditions: Trenches 4 feet or more in depth should be provided with a fixed means of egress Spacing between ladders or others means of egress must be that the worker will not travel more than 25 feet laterally to the nearest egress Ladders must be secure extending a minimum of 36 inches above the landing Metal ladders should not be used when electrical utilities are present
20 Improper Means of Egress A stairway, ladder, or ramp must be present in excavations that are 4 or more feet deep, and within 25 feet of the employees The ladder should extend 3ft above the excavation Two ladders lashed together are not an adequate means of egress
Hazardous Atmospheres If there is any possibility that the excavation could contain a hazardous atmosphere, testing must be conducted prior to entry. (example: Natural gas line may warrant this) Test excavations more than 4 feet before an employee enters the excavation for: Oxygen deficiency High combustible gas concentration High levels of other hazardous substances All operations involving atmospheric testing will require Confined Space Entry procedures to be used. Continuous monitoring may be required. Oxygen should be between 19.5% %
22 Water is Hazardous When water is present in an excavation it is extremely hazardous to enter Methods for controlling standing water and water accumulation must be provided
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