Excavation/Trench Safety Tailgate Session

Transcription

1 Excavation/Trench Safety Tailgate Session Over a five year period, 26 California workers were killed and 207 others injured in trench caveins. In almost every instance, the cause of these accidents was a failure to properly shore or slope the trench. Source: Cal/OSHA Cave-ins are perhaps the most feared trenching hazard. But other potentially fatal hazards exist, including asphyxiation due to lack of oxygen in a confined space, inhalation of toxic fumes, drowning, etc. Electrocution or explosions can occur when workers contact underground utilities. Source: Fed OSHA What is an Excavation? An excavation is any man-made cut, cavity, trench, or depression in the earth's surface formed by earth removal. This can include excavations for anything from utility installations and maintenance to roadways. What is a Trench? A trench is defined as a narrow underground excavation that is deeper than it is wide, and no wider than 15 feet (4.5 meters). Dangers of Trenching and Excavation Operations Trenching and excavation work present serious hazards to workers. Cave-ins pose the greatest risk and are more likely to result in worker fatalities. Soil is extremely heavy and may weigh more than 100 pounds per cubic foot. Other potential hazards include: o Falls o Falling loads o Hazardous atmospheres o Underground utilities such as electricity and gas o Adjacent structure instability o Lack of access and egress o Water accumulation o Loose rocks and soil Importance of Pre-Planning Excavation Work Many on-the-job accidents result from inadequate planning. Failing to plan for proper shoring or sloping increases the possibility of a cave-in or other excavation failure. Required Procedures Prior to Conducting Excavation Work: 1. Call Underground Service Alert (USA) at least two (2) working days before the operation. 2. Mark the boundaries of the excavation area with white paint. 3. Wait for confirmation from the following utilities: 1

2 APWA Utility Color Codes Electric Gas-Oil-Steam Communication and Cable TV Water Sewer Reclaimed Water If you don t receive confirmation from all utilities, either by markings on the excavation location, telephone or , call Dig Alert immediately to let them know. Dig Alert will send out a no-show announcement to the utilities and ensure that they either contact the Department of Public Works to let us know there is no conflict, or go out and mark their lines. Required Training: Supervisors overseeing excavation jobs and those completing the Daily Excavation Checklist must complete the Excavation Safety Competent Person Course (16 Hours) Employees who work in excavations must complete the Excavation Safety Awareness Course (8 Hours) Access and Egress: A stairway, ladder, ramp or, other safe means of access and egress must be located no more than 25 feet away from all employees working in the excavation. Title 8, Section 1541(c)(2) Exposure to Traffic: When excavation work exposes employees to traffic hazards, employees shall wear Department Class 3 traffic high visibility safety vests and appropriate Personal Protective Equipment including hard hats and appropriate protective footwear. A traffic control plan shall be prepared for present traffic conditions and adjusted for deficiencies. Traffic control devices shall be placed according to the traffic control plan and in the direction of traffic flow. Upon completion of work, traffic control devices shall be removed against traffic flow. 2

3 Exposure to Falling Loads: No employee shall be permitted underneath loads being lifted in or out of the excavated work areas. Mobile Equipment Operation Areas: When mobile equipment is operating near an excavation and the operator does not have a clear view of the excavation edge, a warning system such as barricades, tape, hand signals, or stop logs shall be used. Hazardous Atmosphere Conditions: An employee trained in the proper use of the four-gas meter shall test the atmosphere in the excavation before employees enter depths greater than 4 feet, where oxygen deficiency (atmospheres containing less than 19.5 percent oxygen) or a hazardous atmosphere exists or could reasonably be expected to exist. Examples of hazardous environments are atmospheres containing a concentration of a flammable gas in excess of 20 percent of the lower flammable limit of the gas, environments with a potential exposure to Hydrogen Sulfide (H 2 S) or Carbon Monoxide (CO). If the atmosphere in the excavation is determined unsafe, allow the excavation to naturally ventilate and retest the atmosphere. Employees shall not enter excavations until they are deemed safe. Atmospheric testing shall be conducted as often as necessary to ensure that the atmosphere remains safe. Protection from Soil: Keep spoils and equipment at least 2 feet from the edge of the excavation. Title 8, Section 1541(j)(2) Daily Inspections: A competent person trained in the 16-hour Excavation Safety-Competent Person Course, must complete the Daily Excavation Checklist (See Attachment 3). The competent person must inspect the excavation and protective systems daily, before the start of work each day, and throughout the day as conditions change. Protective Systems: Employees working in excavations deeper than 5 feet must have a protective system implemented, such as shoring or sloping, except for excavations entirely in stable rock (very rare). A competent person may require a protective system in excavations less than 5 feet deep if there is a potential for a cave-in. Protective systems shall have the capacity to resist all intended or expected loads. A registered professional engineer must design protective systems for excavations over 20 feet deep. There are three support systems available to protect employees working in excavations (See Key Definitions for additional Information). These include: 3

4 Sloping This method involves sloping the existing face back to an established angle to prevent cave-ins. The soil shall be classified by a competent person to determine appropriate slope. Type C soil requirements shall be used if soil is not classified. Shoring must be installed according to the charts in the Cal/OSHA standard or the manufacturer s instructions which must be readily available on the jobsite. Shielding Trench shields or portable trench boxes help reinforce wall stability. Use this method when shoring is not practical. Shielding must be installed according to the manufacturer s instructions. Note: If the end of a trench over 5 feet in depth is not adequately sloped, benched or shielded, end shoring must be installed. The end shoring must be installed to withstand the pressure exerted along the sides of the trench, or in a manner that will provide equivalent structural restraint. Shoring Shield/Trench Box Sloping Note: A Registered Civil Engineer can sign and stamp an alternate design for a support system, shield system, or other protective system. For Excavation/Trench Policy Questions or Assistance: Contact your Divisional Safety Coordinator and Employee Health and Safety Representative. 4

5 Key Definitions: Competent Person. A competent person is someone who has completed the Department s Excavation Competent Person training, can recognize a hazard associated with trenching/excavation work and has the authority to take prompt corrective action on the job as conditions warrant. Benching. A method of protecting employees from cave-ins by excavating the sides of an excavation to form a series of steps, usually with vertical or near-vertical surfaces between levels. Cave-in. The separation of a mass of soil or rock material from the side of an excavation, or the loss of soil from under a trench shield or support in sufficient quantity so that it could entrap, bury, or otherwise injure and immobilize an employee. Failure. The breakage, displacement, or permanent deformation of a structural member or connection so as to reduce its structural integrity and its supportive system. Shield System. A structure that is able to withstand the forces imposed on it by a cave-in and thereby protects employees within the structure. Support System. A structure such as underpinning, bracing, or shoring, which provides support to an adjacent structure, underground installation, or the sides of an excavation. Sheeting. The members of a shoring system that retain the earth in position and in turn are supported by other members of the shoring system. Uprights. The vertical members of a trench shoring system placed in contact with the earth and usually positioned so that individual members do not contact each other. 5

6 Attachment 1

7 Quiz True or False? 1. Soil may weigh more than 100 pounds per cubic foot. T F 2. It is not necessary to contact Underground Service Alert. Only the local utilities protection service needs to be contacted. T F 3. Training is not required for supervisors overseeing excavation jobs T F because they are not actually doing the work. 4. Many on-the-job accidents result from inadequate initial planning T F 5. Shoring, sloping, and shielding are three types of protective systems T F that allows employees to work in a safe environment. Answer Key 1 T 2 F 3 F 4 T 5 T

8 Attachments 2 & 3 Case Studies

9 ~ :,-.,-? X~ xtai U.S. Department of Labor ~ 'fit,~ ~ ~~ ~ ~ ~ Y'j '~ ACCIDENT SUMMARY. No. 4i. BRIEF DESCRIPTION OF ACCIDENT Four employees of a mechanical contractor were laying a lateral sewer line at a building site. The foreman, a plumber by trade, and a laborer were laying an eight-inch, 20-foot long plastic sewer pipe in the bottom of a trench 36 inches wide, nine feet deep, and approximately 50 feet long. The trench was neither sloped nor shored, and there was water entering it along a shale seam near the bottom. The west side of the trench caved in near the bottom, burying one employee to his chest and completely covering the other. Rescue operations took two and five hours -too late to save the men. INSPECTION RESULTS Following its inspection, OSHA cited the employer for one serious violation and one repeat violation of its construction standards. Had the regulation requiring sloping or shoring of the trench been followed, these men would have been protected against possible collapse of the trench. ACCIDENT PREVENTION RECOMMENDATIONS Employers must instruct employees to recognize and avoid unsafe conditions associated with their work [29 CFR (b)(1)]. Sides of trenches in unstable or soft material more than 5 feet in depth must be shored, braced, sloped, or otherwise supported to protect employees working within them [29 CFR (b)]. NOTE: The case here described was selected as being representative of fatalities caused by improper work practices. No.special emphasis or priority is implied nor is the case necessarily a recent occurrence. The legal aspects of the incident have been resolved, and the case is now closed.

10 U.S. Department of Labor Occupational Safety & Nealfh Administration -~ - ~ - - _ ~ ~ } ~~~1C~F~~~7 REP03tT' ~~ _~' ~ lam= ~...'... _ ~~;-.~ ~ ~ ~ ~4~,.f,~ ACCIDENT SUMMARY No. 61,- E BRIEF DESCRIPTION OF ACCIDENT ~~ { An employee was working in a trench 4 feet wide and 7 feet deep. About 30 feet away a backhoe F was straddling the trench when the backhoe r operator noticed a large chunk of dirt falling from the side wall behind the worker in the trench, he called out a warning. Before the worker could climb out, 6 to 8 feet of the trench wall had f~,f ~ collapsed on him and covered his body up to his ~ t!' neck. He suffocated before the backhoe operator ~r could dig him out. There were no exit ladders. No sloping or shoring had been used in the ~~ trench. I_ a ~ `,..~~. ~ ~, i+~ ~i r ;~~ 4 ~~1 h f i~ ~ ~, ~~ `I j ~ 4, j" F~ ~ 1 1,_ INSPECTION RESULTS As a result of its investigation, OSHA issued citations alleging three serious violations. OSHA's construction standards include several requirements which, if they had been followed here, might have prevented this fatality. ACCIDENT PREVENTION RECOMMENDATIONS The employer did not instruct each employee in the recognition and avoidance of unsafe conditions and the regulations applicable to the work environment to control or eliminate any hazard or other exposure to illness or injury [29 CFR (b)(2)] 1. The employer should not allow work in trenches where the sides were not shored or otherwise supported when the trench is S feet or deeper and 8 feet or longer [29 CFR (a)]. 2. The employer allowed workers in trenches more than 4 feet deep without adequate means of exit, such as a ladder or steps [29 CFR (c)(2)]. (VOTE: The case here described was selected as being representative of fatalities caused by improper work practices. No special emphasis or priority is implied nor is the case necessarily a recent occurrence. The legal aspects of the incident have been resolved, and the case is now closed.