Excavation and Trenching Safety

Transcription

1 Excavation and Trenching Safety

2 References EM Section CFR ; Subpart P UFGS (Latest) Manufacturer s Recommendations Accident Abstracts

3 Potential Contractor Mishap Outcomes Cave-ins Fires, Explosions, Electrocutions and Engulfment due to utility hits Struck by falling objects Falls and Equipment rollovers Asphyxiation, toxic exposures, and explosions due to hazardous atmospheres Leading to property damage, injury, death

4 A Trenching Tragedy Had a false sense of security Knew they were out of compliance Thought the soil was stable Conditions changed overnight A worker died

5 Trenching Statistics About 400 U.S. workers die in trenchrelated accidents each year About 6,400 are seriously injured

6 What Is a Trench? A narrow excavation that is deeper than it is wide No more than 15 feet wide at bottom Walls will eventually fail

7 Introduction Cave-ins are much more likely to result in worker fatalities than other excavation-related accidents. 90% of all violations related to lack of cave-in protection involved manhole installations During inspections where these violations were cited, the excavations were nearly vertical

8 Excavation/Trenching Plan Excavation/trenching plan will be submitted and accepted by the GDA prior to beginning operations.

9 Conditions Excavations/trenches < 5ft (1.5m) in depth, AHA is required but Plan optional Excavations/trenches > 5ft (1.5m) in depth, AHA and Plan required

10 Plan Contents Identification and credentials of CP Diagram or sketch of area where work to be done indicating adjacent structures Projected depth of excavation Projected soil type and method of testing Planned method of shoring, sloping and/or benching Planned method of confined space entry, access, egress, and atmospheric monitoring process Location of utility shut-offs (if required) Method for preventing overhead utility line damage, tree to remain, or other features to remain Management of excavated soil/asphalt/concrete Traffic control Digging permits UXO clearance certificate Controlled flooding plan.

11 Fatal Mishap Trench was 7 ft. deep and 4 ft. wide. Backhoe was 30 ft. away straddling trench. The operator saw the collapse. No protective system Worker died.

12 Excavation Requirements This image cannot currently be displayed. Remove all surface encumbrances Determine location of all underground utilities before opening excavation Use safe means to determine exact locations & protect underground utilities If required, obtain Digging Permit

13 Excavation Inspections Competent person. Inspected daily. As needed through out shift. After every rainstorm or other hazard- increasing occurrence. If cave-in hazard identified, work stopped, workers removed!

14 Definitions Competent Person for Excavations: Training, experience, and knowledge Ability to detect. Authority to take prompt corrective measures to eliminate existing and predictable hazards and to stop work when required.

15 Requirements for protective systems Protective systems shall have the capacity to resist without failure all loads that are intended or could reasonably be expected to be applied or transmitted to the system. 25.A.03.e

16 Requirements for protective systems Provide full worker protection from cave-ins except: -Excavation completely in stable rock -Less than five feet deep & CP determines no potential for cave-in

17 Protection from Water Precautions required before working for water in excavations CP must monitor control measures If diverting surface water must take steps to prevent water from entering trench

18 Trenching And Excavations Protection From Water-25.A.06 Water in excavation

19 Trenching And Excavations Protection From Water-25.A.06 Water in excavation

20 Trenching And Excavations Protection From Water-25.A.06 Water in excavation

21 Water in trench Employees shall not work in excavations in which there is accumulated water or in which water is accumulating unless the water hazard posed by accumulation is controlled. 25.A.06.b

22 Falling Soil or Equipment Protect workers from loose rock/soil that may fall from an excavation face Use scaling to remove loose soil Use protective barricades, such as shoring or shields Protect workers from material or equipment that could fall into the excavation Keep material/equipment 2 feet from edge Use retaining devices

23 Protection from Falling Materials

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25 Equipment-Vehicle Precautions Barricades and substantial stop logs for mobile equipment operating near excavations

26 Equipment-Vehicle Precautions Excavating or hoisting equipment shall not be allowed to raise, lower, or swing loads over or adjacent to personnel in excavation without substantial overhead protection. 25.A.08.c

27 25.A.09 - Requirements for protective systems No working on sloped or benched faces unless employees below are protected

28 Safe Access - 25.B Workers, vehicles, equipment and the public must be protected. The public,vehicles or equipment require class I perimeter guarding. Greater than 6 feet or other hazard and worker exposure requires class II guarding. If none of the above, at least class III. See definitions for type I, II, III guarding.

29 Safe Access-25.B.01 Perimeter Protection Required Class I - Members of the Public or Vehicles Class II - Contractor Employees/>6 or Contain Hazard Class III - <6, No Hazard, No Routine Contractor Employee Exposed

30 Safe Access Perimeter Protection Criteria Class I - Standard Guardrail/Barriers Withstanding Impact Loads Class II - Warning Barricades/Flagging Not Closer Than 6 From Edge Class III - Warning Barricades/Flagging 6 to 6 From Edge

31 Safe Access-25.B.03 - Excavations shall be backfilled as soon as possible.04 - Walkways or bridges with guardrails shall be provided where people or equipment are required or permitted to cross over excavations

32 Safe Access Stairway, ladder, ramp or other safe means of egress shall be located in trench excavations that are 4 feet or more in depth to require no more than 25 feet of lateral travel for employees. 4' or greater Every 25'

33 Safe Access-25.B.05/07 At least two means of exit shall be provided for personnel working in excavations Width of excavation exceeds 100 ft 2 or more means of exit for each side Excavations 20 feet or more in depth Ramps, Stairs, or mechanical personnel hoists Ladders used as access ways Shall extend 3 feet above the surface

34 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

35 What is wrong/right with this picture?

36 Ramps solely for personnel access shall be a minimum width of 4 ft (1.2 m.) and provided with standard guardrails Ramps for equipment shall be 12 ft min. Ladders used as access ways shall extend 3 ft from bottom of excavation Ramps

37 What Is a Cave-in? Soil or rock that suddenly falls or slides into an excavation Sufficient quantity to 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

38 Cave-in Injuries Soil weighs 125 lbs. per cubic foot A worker can be crushed by soil, rock, or an object Suffocation even if worker s head is not buried, soil prevents chest expansion Worker becomes immobilized by soil s suction effect

39 Sloping and Benching Options Excavations less than 20 feet deep, maximum slope shall be 34 degrees measured from the horizontal (1 1/2 horizontal to 1 vertical). Design selected from tabulated data (OSHA s standard, Mfg s specification) Designed or approved by registered professional engineer.

40 Sloping and Benching Sloping: angling of walls at an incline Benching: series of steps to angle walls Soil type determines angle of slope/bench Type A: 3 feet horizontal to 4 feet vertical (3/4:1) Type B: 4 feet horizontal to 4 feet vertical (1:1) Type C: 6 feet horizontal to 4 feet vertical (1-1/2:1) Benching not permitted for Type C soil

41 Support System Options Timber, hydraulic and mechanical shoring systems etc.. Designs drawn form manufacturer s tabulated data. From tabulated data (such as tables and charts such as OSHA s Standard). Designed or approved by a registered professional engineer.

42 25.D.02- Requirements for support systems Materials for protective systems free from damage & defects Used according to manufacturers specifications If damaged CP must determine suitability for continued use

43 25.D.03 Installation and Removal of Support Systems Support system members securely connected together Installed & removed to assure employee safety Support systems not subjected to loads exceeding their capacity

44 125.D.03.e Removal of Support Systems Removal of support systems from bottom up Backfilling progresses with the removal of shoring

45 Additional Requirements for Trenching Excavation of up to 2 feet underneath support system allowed only if: System designed for support of full depth No evidence of loss of soil loss behind or below 2'

46 Soil Classification 29 CFR 1926 Appendix A (b)(2) Sloping & Benching (c) Protective Systems Competent Person Visual Test Manual Test

47 Soil Classification 29 CFR 1926 Appendix A Visual Test Observe soil as it is excavated. Soil that remains in clumps when excavated is cohesive. Soil that breaks up easily and does not stay in clumps is granular. Manual Test Penetrometer, Shear Vane, Plasticity, Dry Strength, Thumb Penetration.

48 Soil Classification Grain size Saturation Cohesiveness Unconfined compressive strength

49 Soil Types Type A (most stable) dense and heavy clay Type B silt, sandy loam, medium clay Type C (least stable) gravel, loamy sand, soft clay

50 Fatal Shoring Related Mishap Good example of a poorly designed system. 8 x15 x3/4 Steel plates leaning at 30 degrees against bank. No supports Not approved, no tabulated data used.

51 Trench Shield A trench shield was built around this work area

52 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

53 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.

54 Summary Tone before you dig. Get a dig permit where applicable. Classify soil and install proper protection prior to entry of trench or excavation. Provide fall protection for employees exposed to falls of 6 feet or greater. Provide members of the public protection.