Published on January 19, 2008
Excavations: Excavations Excavation Hazards: Excavation Hazards Cave-ins are the greatest risk Other hazards include: Asphyxiation due to lack of oxygen Inhalation of toxic materials Fire Moving machinery near the edge of the excavation can cause a collapse Accidental severing of underground utility lines Injury and Death: 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 Definitions: 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. Slide5: Focus of Training The greatest risk at an excavation How to protect employees from cave-ins Factors that pose a hazard to employees working in excavations The role of a competent person at an excavation site Protection of Employees: Protection of Employees Employees should be protected from cave-ins by using an adequately designed protective system Protective systems must be able to resist all expected loads to the system Requirements for Protective Systems: Requirements for Protective Systems A well-designed protective system Correct design of sloping and benching systems Correct design of support systems, shield systems, and other protective systems Plus Appropriate handling of materials and equipment Plus Attention to correct installation and removal Equals Protection of employees at excavations Design of Protective Systems: 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 Protect Employees Exposed to Potential Cave-ins: Protect Employees Exposed to Potential Cave-ins Slope or bench the sides of the excavation, Support the sides of the excavation, or Place a shield between the side of the excavation and the work area Slide10: Cave-in Hazard This excavation has inadequate support posts and egress access Inadequate protective system Inadequate Protective System : Inadequate Protective System Factors Involved in Designing a Protective System: Factors Involved in Designing a Protective System Soil classification Depth of cut Water content of soil Changes due to weather and climate Other operations in the vicinity Shoring: Shoring General Provides a framework to work in Uses wales, cross braces and uprights Supports excavation walls OSHA tables provide shoring data Must know soil type Must know depth and width of excavation Must be familiar with the OSHA Tables Trench Shield: Trench Shield A trench shield was built around this work area Hydraulic Trench Support: Hydraulic Trench Support Using hydraulic jacks the operator can easily drop the system into the hole Once in place, hydraulic pressure is increased to keep the forms in place Trench pins are installed in case of hydraulic failure Materials and Equipment: 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. Protection from Vehicles: Protection from Vehicles Install barricades Hand/mechanical signals Stop logs Grade soil away from excavation Fence or barricade trenches left overnight Slide18: Hazardous Conditions The weight and vibrations of the crane make this a very hazardous condition. They should not be working under this crane. Spoils: Spoils Don’t place spoils within 2 feet from edge of excavation Measure from nearest part of the spoil to the excavation edge Place spoils so rainwater runs away from the excavation Place spoil well away from the excavation Slide20: Other Excavation Hazards Water accumulation Oxygen deficiency Toxic fumes Access/Egress Falls Mobile equipment Water is Hazardous: Water is Hazardous When water is present in an excavation it is extremely hazardous to enter Note that these workers are not wearing hardhats to protect them from materials falling into the trench Water = Cave-in Hazard: Water = Cave-in Hazard These workers must be protected from cave-in. Note the water in the bottom of the trench. This is a very hazardous condition! Hazardous Atmosphere: Hazardous Atmosphere 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 Means of Egress: 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 This ladder does not meet the requirements of the standard The ladder should extend 3 feet above the excavation Slide25: Access and Egress These two ladders which are lashed together are not an adequate means of egress The ladder should extend 3 feet above the top of the excavation Protection from Falls, Falling Loads, and Mobile Equipment: Protection from Falls, Falling Loads, and Mobile Equipment Install barricades Use hand / mechanical signals Grade soil away from excavation Fence or barricade trenches left overnight Use a flagger when signs, signals and barricades are not enough protection Slide27: Competent Person Must have had specific training in and be knowledgeable about: Soils classification The use of protective systems The requirements of the standard Must be capable of identifying hazards, and authorized to immediately eliminate hazards Inspections of Excavations: Inspections of Excavations A competent person must make daily inspections of excavations, areas around them and protective systems: Before work starts and as needed, After rainstorms, high winds or other occurrence which may increase hazards, and When you can reasonably anticipate an employee will be exposed to hazards. Inspections of Excavations: Inspections of Excavations If the competent person finds evidence of a possible cave-in, indications of failure of protective systems, hazardous atmospheres, or other hazardous conditions: Exposed employees must be removed from the hazardous area Employees may not return until the necessary precautions have been taken Site Evaluation Planning: Site Evaluation Planning Before beginning excavation: Evaluate soil conditions Construct protective systems Test for low oxygen, hazardous fumes and toxic gases Provide safe in and out access Contact utilities Determine the safety equipment needed Fissure Slide31: Summary The greatest risk in an excavation is a cave-in. Employees can be protected through sloping, shielding, and shoring the excavation. A competent person is responsible to inspect the excavation. Other excavation hazards include water accumulation, oxygen deficiency, toxic fumes, falls, and mobile equipment.