Safety Meeting Topic #21 Trenches/Excavations

Transcription

1 Safety Meeting Topic #21 Trenches/Excavations Excavation and trenching cave-ins result in more than 100 fatalities annually in the United States. With little or no warning, an unsupported, improperly-shored or sloped trench or excavation wall can collapse, trapping workers below in seconds. Let s talk a little more about the high cost of a cave-in. Have you ever witnessed a cave-in that buried a worker? Do you know that one cubic yard of soil weighs approximately 3,000 pounds (the equivalent of a Volkswagen)? And do you know what happens to a human body when 3,000 pounds of soil explodes onto it. Within two seconds there is probably no life left in that body. Most trench collapses don t result in broken fingers, abrasions, or twisted knees. Most trench collapses take lives. The facts are that simple. Before starting a job, the following conditions should be considered: traffic, nearness and condition of structures, soil, surface and ground water, the water table, overhead and underground utilities, and weather. Soils OSHA s standards describe three basic types of soils: A Soil, B Soil, and C Soil. A Soil has compressive strengths of 1.5 tons per square foot or greater. It is very cohesive, and only has to be laid back at a ratio of 3/4:1 to maintain a safe working angle. B Soil has compressive strengths of.5 to 1.5 tons per square foot. It is moderately cohesive, but must be laid back at a ratio of at least 1:1 to maintain a safe working angle. C Soil, on the other hand, is so unstable (uncohesive), and has an unconfined compressive strength of.5 or less, and therefore must be laid back at a ratio of 1 1/2:1 to maintain a safe working angle. Since the bulk of the soil that all of us work in is C Soil, it means that we re constantly threatened with the dangers ever present in extremely unstable soil, where the slightest jar, vibration, rain/moisture, etc., can cause the side walls to collapse at the slightest provocation. Therefore, a competent person in our industry needs to have a thorough knowledge and understanding of the inherent dangers surrounding trenching operations, and must therefore apply the protective steps provided by OSHA in its 1926 (Subpart P) Standards.

2 OSHA Standard (k)(1) requires that every trench and or excavation must be inspected daily by a competent person (someone who is trained and knowledgeable and has authority to take corrective action), prior to the start of work and as needed throughout the work shift. A safe trench or excavation must adhere strictly to all plans and specifications. Soil conditions must be monitored for changes and location of all existing utilities is mandatory. A safe means of entry and exit is required if the trench is deeper than 4 feet. See standard for specifics. Any of the following could affect your safety when in a trench or excavation: WARNING SIGNS OF FAILURE: Tension cracks in sidewalls, slopes, and surface adjacent to excavations; Ground settlement or subsidence; Spilling or sloughing soils; Changes in wall slope or bulge; Increase in strut loads; excessive seepage and piping of fine soils; Softening of sidewalls or boiling of trench bottom; Creaking or popping sounds; Visual deformation of bracing system or trench. SLOPING / BENCHING - CHECK FOR: Excessive vibration; location of spoil pile and backfill; signs of distress cracking, bulging, etc.; improper installation procedures or alignment of members; incorrect installation of connections; workers in unbraced trench or improper system of bracing being used. SHORING / BRACING - CHECK FOR: Maintenance of proper slope ratio; excessive vibrations; location of spoil pile, trees, boulders or structures; equipment location relative to the excavation; secondary soil or rock structure; presence of water seepage and/or rainfall; signs of distress. TRENCH SHIELD / BOX - CHECK FOR: Clearance between shield and trench sidewalls; adequate freeboard at top of shield; proper slope above shield; current certification of shield; excessive wear or damage, or improper use of shield; workers in an unshielded trench or improper shield being used. SAFETY REMINDERS: THE COMPETENT PERSON MUST BE KNOWLEDGEABLE. TRAINED, AND HAVE THE AUTHORITY TO TAKE CORRECTIVE ACTION. Trench Shield: Has one role in life: To protect the workers in the trench system. Ladder: To provide safe egress to and from a trench shield, that there be a ladder. Inside Trench: The ladder must be immediately accessible to the workers in the trench (and must never be placed outside the shield system). Hard Hats: A small pebble or hand-tool falling on a worker in a trench can cause concussions, skull fractures, death. Wear em.

3 Locked in Place: Aluminum hydraulic shores, when expanded, must lock in place. Improper Installation/Dismantling: Aluminum hydraulic shoring, as well as timber shoring must be assembled from the top down, and disassembled from from the bottom up. Ramps: It s okay to use ramps to enter and exit a trench, providing the ramp surface is compacted, is not wet, and can be accessed in an upright position. More Information For more detailed information regarding company policies and procedures, refer to the Hayward Electric Injury & Illness Prevention Program manual, Chapter 11, Excavations and Trenching.

4 Name Date SAFETY MEETING # 21 - TRENCHES/EXCAVATION TRAINING QUIZ 1. OSHA=s standards describe six types of soil. 2. Type AB@ soil has compressive strengths of. A..5 to 3.5 tons per square foot or greater B..5 to 1.5 tons per square foot or less C. 1 to 3.5 tons per square yard or greater D..5 to 1.5 tons per square foot or greater 3. Type AA@ soil should be laid back at a ratio of.75:1 to maintain a safe working angle. 4. Type AC@ soil is very stable. 5. A cubic yard of soil weighs. A. 1 ton B. 3 tons C. 5 tons D. 1.5 tons 6. A collapse of a cubic yard of soil can kill a person within two seconds. 7. Most job sites have type AC@ soils. 8. Trenches/excavations can be undermined by. A. Vibrations B. Rain/moisture C. Underground seepage D. All of the above 9. Hayward Electric provides detailed information regarding trenches/excavations in the I&IPP book. 10. OSHA requires a knowledgeable competent person to protect all trenches and excavations at all times.

5 11. There must be a safe means of entry and exit for trenches over feet deep. A. 2 B. 4 C. 6 D Workers in trenches can enter/exit by means of: A. A ladder inside the trench shield B. A ladder outside the trench shield C. a ramp that is wet D. None of the above 13. Creaking or popping is a warning sign of trench failure. 14. OSHA requires that a trench be inspected once a week. 15. If the slope ratio is compromised a trench could collapse.