«Leaders Guide Trenching and Shoring Safety - Competent Person The manual for Excavations Trenching and Shoring is produced in Adobe Acrobat. The ...»
A. Prevent material from being kicked onto workers B. Prevention of accidental falls IMPORTANT Super-imposed loads, (spoil, pipe, vehicles, equipment and material) can affect trench stability. This will require that the distance soil or material is kept from the edge of the trench, increases as the trench depth increases.
For example: In a 5 foot trench, material must be kept a minimum of two feet from the edge of the trench. For every additional 5 feet, the distance must be increased by an additional 2feet.
If non-native material will be back filled and it is possible to transport spoil away from the site, this option should be seriously considered.
Inspectors The competent person must conduct frequent inspections of the excavation site starting at the beginning of the day and periodically throughout the shift. Additional inspections must also be performed after any hazard increasing event such as rain storms, Santa Ana conditions, traffic, earthquake tremors, etc.
DAILY MINIMUM INSPEC TIONS
Daily (Minimum) inspections by the Competent Person include:
Trenches Soil Excavations Protective systems Water control systems Surrounding areas The Competent Person must inspect the trench or excavation for any evidence of any
situation which could result in:
Cave-ins Indications of a trench protective system failure Hazardous Atmospheres Other hazardous conditions Where there is evidence of a potential cave-in or other hazardous condition, the Competent Person must remove the affected employees until the necessary precautions have been taken to assure safety.
Competent Person Checklists for Trenching and Excavation Checklists for Trenching and Excavation Competent Person and an Excavation Safety: Daily Inspection are provided. They request information about the contract name and number, contractor or subcontractor, government inspector; location of the project, contractor inspector and date the checklist is filled. The form also contains information about the competent person, general topics, water conditions, egress, and confined spaces. The first checklist is based on EM 385-1-1, dated 3 September 1996. Use of this checklist is optional. The second checklist is dated18 Nov 2005 (updated 18 Sep 2008) SLAC-I-730A23J-003-R001.
The two checklists are separated by section breaks and can be copied as a document to carry into the field.
TRENCHING AND EXCAVATION COMPETENT PERSON CHECKLIST
Competent Persons Name:
Length of experience in this occupation:___________________________
Length of experience with this employer:
Does the designated individual have training in:
Use of protective Systems?
Requirements of 29 CFR 1926.650-652?
List Training Experience:
Does the designated individual have knowledge about:
Soil Analysis? (Describe types of soils and properties) Use of protective systems? (What method is being used and how was it determined) Requirements of 29 CFR 1926.650-652?
Does the designated individual have authority to:
Take prompt corrective action to eliminate existing and predictable hazards?
When was the last inspection of the excavation conducted?
Was an inspection done and documented prior to the start of work?
Were inspections done and documented as needed throughout the work shift?
Were inspections done and documented after rainstorms or other hazard-increasing occurrence?
Is the excavation deeper than 4 feet?
Is dewatering equipment being used on the site?
If yes, is the competent person monitoring the equipment and its proper operation?
Has the excavation been subject to water accumulation?
Has the soil in the trench been adversely affected?
If yes, has the competent person inspected the excavation and taken actions?
Is a means of egress (exit) provided every 25 feet?
Is a ramp used for access or egress to the excavation? (If no, skip to the next section.) Is the ramp used solely for employee access?
If yes, was it designed by a competent person for safe access and egress?
If yes, is the competent person who designed the ramp qualified?
Does the ramp meet specifications?
Is there a potential for a hazardous atmosphere in the trench? If not, why?
Is air monitoring equipment on site?
Has a qualified person been assigned to assess the hazards of confined space?
(OSHA Definition: A Qualified Person is designated by the employer in writing, as capable (by education and/or specialized training) of anticipating, recognizing and evaluating employee exposure to hazardous substances or other unsafe condition in a confined space. This person shall be capable of specifying necessary control and/or protective equipment to ensure safety.) Is emergency rescue equipment as outlines in 29 CFR 1926.651 (g)(2)(I) readily accessible to employees?
___________________________________________________ __________ Printed Name of Competent person Table 2 Competent Person Checklist for Trenching and Shoring Excavation Safety: Daily Inspection Checklist Department: Chemical and General Safety Program: Excavation Safety Owner: Program Manager Authority: ES&H Manual, Chapter 11, Excavation Safety1 The following checklist is to be completed by the excavation competent person (and the checklist signed by a project manager / university technical representative for subcontracted work) for required daily inspections of excavation operations, defined in Chapter 11, “Excavation Safety”, as “operations where contact with soil is expected, such as trenching and removing soil”, that meet any of the following
conditions, at any time:
1. Are one foot or more in depth
2. Involve the use of power tools
3. In which utilities are identified or any hazardous conditions are likely to be encountered
See Excavation Safety: Excavation Procedures for more information.2
Job Site Location ___________________________ Permit Number___________________
Date of Inspection___________________________ Time of Inspection________________
Competent Person___________________________ Phone___________________________
____ Prior to Start of Work (Daily) Routine Inspection during Work ____ After Rainstorm After a Hazardous Condition (Explain) ______________________________________________________________________________
Other (Explain) ______________________________________________________________________________
Weather_______________ Traffic______________________ Terrain______________________
Spoil Location_________________________ Building Proximity _________________________
Heavy Equipment Location ______________Heavy Materials Location ____________________
Water Accumulation ____________________Possible Vibration Sources ___________________
Utilities Located ____ Proper Markings in Place ____ Previously Disturbed Soil _____ Trench Width __________ Trench Depth ____________
1 SLAC Environment, Safety, and Health Manual (SLAC-I-720-0A29Z-001), Chapter 11, “Excavation Safety”, http://www-group.slac.stanford.edu/esh/hazardous_activities/excavations/policies.htm 2 Excavation Safety: Excavation Procedures (SLAC-I-730-0A23C-001), http://wwwgroup.slac.stanford.edu/esh/eshmanual/references/excavationsProcedAll.pdf
Other Trench Characteristics ______________________________________________________
Atmospheric Test Results ________%O2 % LEL ____________
Toxic Source of Hazardous Atmosphere _____________________________________________
Soil Analysis Method(s) Used (Check all that apply) _____Visual ______Manual ______Tabulated Data Soil Characteristics (Check all that apply) _____Cemented _____Cohesive _____Dry _____Fissured _____Granular _____Layered _____Moist _____Plastic _____Saturated _____Submerged Soil Classification (Check all that apply) _____Type A _____Type B _____Type C _____Stable Rock Avg. Compressive Strength _____tsf Compressed Strength Data __________ Manual Test Used (Check all that apply) _____Plasticity _____Dry Strength _____Thumb Penetration _____Pocket Penotrometer _____Drying Test _____Other ___________________________________
______ Option (1) slope is 1.5:1 (34°) (Type C) ______ Option (2) slope is ______ based on soil type ______ Trench Shield: Manufacturer Name _______________________________________
______ Aluminum Hydraulic Shoring System: Manufacturer Name: ____________________
Supporting Information: _______________________ Tabulated Data on Site: ___________ General Is excavation within original scope of excavation permit? ___ Yes ___ No Are recommendations for disposal, shielding, and training from excavation permit being adhered to? ___ Yes ___ No Utility survey markings legible? ___ Yes ___ No Storm drains adequately protected from sediment? ___ Yes ___ No Stockpiles/excavated materials at least two feet from edge of excavation? ___ Yes ___ No
Describe any changing conditions, plans, or shoring equipment damage:
Excavation Competent Person _______________________________________________________________
Project Manager / University Technical Representative ________________________________________________________________
18 Nov 2005 (updated 18 Sep 2008) SLAC-I-730-0A23J-003-R001 2 of 2 Excavation Safety: Daily Inspection Checklist Table 3 Evacuation Safety: Daily Inspection Checklist Fall Protection Figure 8 Walkway equipped with standard guardrails to allow employees to cross excavations or trenches In situations in which employees are permitted to cross over excavations or trenches walkways or bridges equipped with standard guardrails must be provided.
In cases where there is other potential of falling into an excavation, the general area must be protected by using guard rails or other method to prevent falls.
In cases where projects are in a remote location, all shafts, wells, pits, etc., must be barricaded or covered. Immediately upon completion of the job requiring this type of excavation, the shaft, pit, well, etc., must be back filled.
OVERVIEW: SOIL MECHANICS.A number of stresses and deformations can occur in an open cut or trench. For example, increases or decreases in moisture content can adversely affect the stability of a trench or excavation. The following diagrams show some of the more frequently identified causes of trench failure.
TENSION CRACKSTension cracks usually form at a horizontal distance of 0.5 to 0.75 times the depth of the trench, measured from the top of the vertical face of the trench. See the accompanying drawing for additional details.
TOPPLINGIn addition to sliding, tension cracks can cause toppling. Toppling occurs when the trench's vertical face shears along the tension crack line and topples into the excavation.
SUBSIDENCE AND BULGINGAn unsupported excavation can create an unbalanced stress in the soil, which, in turn, causes subsidence at the surface and bulging of the vertical face of the trench. If uncorrected, this condition can cause face failure and entrapment of workers in the trench.
HEAVING OR SQUEEZINGBottom heaving or squeezing is caused by the downward pressure created by the weight of adjoining soil. This pressure causes a bulge in the bottom of the cut, as illustrated in the drawing above. Heaving and squeezing can occur even when shoring or shielding has been properly installed.
Figure 13 Graphic Illustrating Heaving or Squeezing
BOILINGBoiling is evidenced by an upward water flow into the bottom of the cut. A high water table is one of the causes of boiling. Boiling produces a "quick" condition in the bottom of the cut, and can occur even when shoring or trench boxes are used.
UNIT WEIGHT OF SOILSUnit weight of soils refers to the weight of one unit of a particular soil. The weight of soil varies with type and moisture content. One cubic foot of soil can weigh from 110 pounds to 140 pounds or more, and one cubic meter (35.3 cubic feet) of soil can weigh more than 3,000 pounds.
Determination of Soil Type Four Soil Types as Defined by OSHA OSHA categorizes soil and rock deposits into four types, as follows
STABLE ROCKStable Rock is natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed. It is usually identified by a rock name such as granite or sandstone. Determining whether a deposit is of this type may be difficult unless it is known whether cracks exist and whether or not the cracks run into or away from the excavation.
TYPE A SOILS
Type A Soils are cohesive soils with an unconfined compressive strength of 1.5 tons per square foot (tsf) (144 kPa) or greater. Examples of Type A cohesive soils are often: clay, silty clay, sandy clay, clay loam and, in some cases, silty clay loam and sandy clay loam. (No soil is Type A if it is fissured, is subject to vibration of any type, has previously been disturbed, is part of a sloped, layered system where the layers dip into the excavation on a slope of 4 horizontal to 1 vertical (4H:1V) or greater, or has seeping water.
TYPE B SOILS