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This presentation discusses excavation and trenching safety. It outlines the key safety requirements including proper sloping, shoring or benching of trench walls based on soil type and depth. Collapses are the most common accident and can occur rapidly. Proper planning, inspections for cracking or bulging walls, and emergency procedures are essential. Ladders or ramps are required for entry/exit and spoils must be kept back from the trench edge.

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Excavation &Excavation & TrenchingTrenching SafetySafety Presentation by Dan Eschenasy, PE
This presentation was prepared in support of the Department of Buildings Excavation and Trench Safety Guidelines Flyer. It illustrates what, in the author’s opinion, are the most important issues related to excavation and trenching safety. This presentation, as well as the guidelines flyer, are for informational purposes only. All such work must comply with the requirements in the NYC Building Code and the relevant rules and regulations. You must also comply with all relevant federal and state laws. The presentation provides links to these as well as to other relevant Internet publications. WARNINGWARNING
The Department of Buildings has identified excavation and trenching as areas where code compliance needs improvement. The attached flyer is being handed out to remind contractors, workers and the general public of the basic safety rules for excavation and trenching. DOB FlyerDOB Flyer
At about the same time, OSHA published its own card intended to remind the public of the safety rules for trenches. Photo Courtesy OSHA OSHAOSHA
Contractors Shall Comply with both OSHAContractors Shall Comply with both OSHA Regulations and the NYC Building CodeRegulations and the NYC Building Code IT’S THE LAW IT MAY SAVE YOUR LIFE IT’S GOOD ENGINEERING AND BUSINESS PRACTICE
Trench Walls will CollapseTrench Walls will Collapse Typically, trenches are only open for a short period of time (minutes or hours). The walls of any trench will eventually collapse; it is merely a matter of time. Short-term apparent stability is a temptation for a contractor to send workers into a dangerous trench in hopes of rapid progress and financial gain. Death or serious injury can result. http://www.cdc.gov/elcosh/docs/d0200/d000279/ilochap93.html Encyclopaedia of Occupational Health and Safety, fourth Edition Chapter 93 - Construction Jack Mickle, Jack L. Mickle & Associates
38% Cave-in is the most common accident in Excavation & Trenching Trenching/Excavation AccidentsTrenching/Excavation Accidents J. Irizarry et al . Analysis of Safety Issues in Trenching Operations
37 % of all trenching accidents occur at depths less than 5 feet J Irizarry et all . Analysis of Safety Issues in Trenching Operations AccidentsAccidents vsvs. Trench Depth. Trench Depth
Project Value Percent Cumulative 1 Under 50,000 28.51 28.51 2 50,000 - 250,000 18.81 47.38 3 250,000 - 500,000 10.35 57.73 4 500,000 - 1,000,000 8.94 66.67 MostMost FatalitiesFatalities Occur in SmallOccur in Small Construction ProjectsConstruction Projects 28 % 66.6%$1,000,000.00 $50,000.00 AN ANALYSIS OF FATAL EVENTS IN THE CONSTRUCTION INDUSTRY 2000
Most Fatalities Occur:Most Fatalities Occur: •In trenches 5 feet to 14 feet deep •In collapses that developed extremely fast. •Additional [secondary] collapses are very common •Co-workers attempting to rescue someone can also become victims
Analysis of Construction Fatalities - The OSHA Data Base 1985-1989
Plan Before You Start ExcavatingPlan Before You Start Excavating Inspect the site. Collect information. List the risks. Mitigate or eliminate potential problems Establish minimum rate of inspection Have written site safety plan, including emergency procedures
Understand Protection RequirementsUnderstand Protection Requirements Determine project requirements and conditions Understand basic soil identification Understand available protection choices – Benching – Shoring – Terms – Selection – Installation and Removal Understand effects of water
Refer to §27-1032 of the NYC Building Code (www.NYC.gov/buildings) and OSHA’s regulations (www.osha.gov) for details on the proper protection of an excavation or trench.
Soil Identification - GeneralSoil Identification - General •Rock •Gravel •Sand •Silt •Clay •Fill See NYC Building Code Subchapter 11 - Foundations Article 4.
NYC Building Code and SoilNYC Building Code and Soil Classification Intended for Excavation Protection and Sheet Piling – Hard – Likely to crack or crumble – Soft sandy filled in loose soil In most cases the top layer where excavation takes place is fill. It’s worked and placed by man and has undetermined properties.
OSHA Soil Classification SystemOSHA Soil Classification System Soil classification system means, for the purpose of this subpart, a method of categorizing soil and rock deposits in a hierarchy of Stable Rock, Type A, Type B, and Type C, in decreasing order of stability. The categories are determined based on an analysis of the properties and performance characteristics of the deposits and the environmental conditions of exposure http://www.osha.gov/Publications/Homebuilders/Homebuilders.html#subp •Stable Rock •Type A Soils •Type B Soils •Type C Soils •Layered
Continued Visual Determination-Soil ClassVisual Determination-Soil Class Soil class by OSHA is dependent on the condition of the soil in the vicinity of the excavation. Check for: Cracked ground at top or wall of excavation. Fill [earth the was added or disturbed] Excavation soil that is exposed to vibrations from traffic or construction equipment. Poor drainage around excavation or water seepage
Continued Manual TestsManual Tests http://www.osha.gov/Publications/Homebuilders/Homebuilders.html#subp See the NYC Building Code -Table 11-1, Unified Soil Classification & Field Identification Procedures See OSHA Plasticity Dry Strength Thumb penetration
Safety GuidelinesSafety Guidelines Each side of an excavation or trench which is 5 feet or deeper must be protected by sheeting/bracing shoring or sloped unless it is cut from rock
Sloping & Benching -Required ConfigurationSloping & Benching -Required Configuration
Continued Shoring Systems SelectionShoring Systems Selection Soil type must be known Depth and width of the excavation must be known One must be familiar with the NYC Building Code Tables
Building Code Terms for ShoringBuilding Code Terms for Shoring
Excavation eschenasy
OSHA TerminologyOSHA Terminology Photo Courtesy of OSHA
In this case, traffic exerts higher loads on walls of excavation - tables cannot be used.
Deeper excavations require engineered protective systems
Violation Issued: Improper shoring and improper benching.
The condition shown in the previous slide led to sidewalk collapse.
Do not work in an excavation or trench filled with running or standing water.
•Use of special support or shield systems approved by a registered professional engineer. •Water removal equipment, i.e. well pointing, used and monitored by a competent person. •Safety harnesses and lifelines used in conformance with 29 CFR 1926.104. •Surface water diverted away from the trench. Employees removed from the trench during rainstorms. •Trenches carefully inspected by a competent person after each rain and before employees are permitted to re-enter the trench. www.cdc.gov/elcosh/docs/d0100/d000168/d000168.html Accumulating or Standing Water Must Do’sAccumulating or Standing Water Must Do’s
Despite significant shoring -water removal might still damage the adjoining building.
Regularly check the walls of an excavation or trench for cracks, bulges and spalling. Check the shoring for signs of distress -- especially after a rain storm.
•Area at the top of the trench •Trench walls •Excavated area at trench bottom •Excavation protection system Daily Inspections Should Include:Daily Inspections Should Include:
Site Conditions Can Change RapidlySite Conditions Can Change Rapidly Weather conditions. Inspect several times each day in case of : ∗ Heavy rains and flooding ∗ Hot or Cold Temperatures ∗ Heavy Snow or Snow Melting Vibration Dewatering
Photo Courtesy OSHA What and Where to Look?What and Where to Look?
Tension cracks at a collapseTension cracks at a collapse
Do not store spoil, materials or equipment along the edge of an excavation or trench.
Temporary Spoil Pile 2 ft. min.
Excavator left for the weekend too close to the trench edge. The improperly benched excavation might collapse.
Underground Installations - OSHAUnderground Installations - OSHA (b)(1) The estimated location of utility installations, such as sewer, telephone, fuel, electric, water lines, or any other underground installations that reasonably may be expected to be encountered during excavation work, shall be determined prior to opening an excavation. (b)(2) Utility companies or owners shall be contacted .. to locate utility installations. (b)(3) When excavation operations approach the estimated location of underground installations, the exact location of the installations shall be determined by safe and acceptable means. (b)(4) While the excavation is open, underground installations shall be protected, supported or removed as necessary to safeguard employees.
Stability of Adjacent StructuresStability of Adjacent Structures Excavation below the base of an existing foundation is not permitted as the foundation or the excavation wall might collapse. Shoring is required when: •A controlled inspection is required. •A licensed engineer needs to specify procedure and protection. Lack of such measures is one of the major causes of recent building distress and collapse.
Unprotected excavation next to existing building led to bearing wall collapse.
Each open side of an excavation or trench shall have a guardrail or a solid enclosure.
Each excavation or trench shall have a way out such as a ladder or ramp.
Access to and exit from the trench require the : •Trenches 4 ft or more in depth should be provided with a fixed means of egress. •Spacing between ladders or other means of egress must be such that a worker will not have to travel more than 25 ft laterally to the nearest means of egress. •Ladders must be secured and extend a minimum of 36 in (0.9 m) above the landing. •Metal ladders should be used with caution, particularly when electric utilities are present. Trench Ingress and EgressTrench Ingress and Egress
Continued Special AttentionSpecial Attention Removal of excavation support systems must be planned and usually proceed from the bottom up. Placing as well as removal of shoring or protecting systems shall be executed without inducing collapse. Must backfill together or immediately after removal of support system. Must follow specifications. All shoring members or any other protecting system shall be assembled together as per specs. Various elements of the support systems must be securely connected together and shall not be subjected to loads beyond their capacity such as those resulting from large vehicles or equipment.
•Installation of the support system is closely coordinated with the excavation of the trench. [1541.1(d)(1)] •Workers are protected from cave-ins, structural collapse, or accidentally being hit during installation and removal of the support system. [1541.1(e)(1)(E)] • Removal of shoring or other protective systems starts at the bottom of the excavation. Members are released slowly so structural failures will be noticed. [1541.1(e)(1)(E)] •Backfilling progresses with the removal of support systems from excavations. [1541.1(e)(1)(F)] Trenches and Excavations Checklist - http://www.cdc.gov/elcosh/docs/d0200/d000246/d000246.html Special AttentionSpecial Attention
Trench RescueTrench Rescue Often, one death or severe injury in a trench is compounded by a poorly thought-out rescue attempt. The victim and rescuers may become trapped and overcome by deadly gases, fumes or lack of oxygen; drowned; or mutilated by machines or rescue ropes. With failed rescue attempts, most of the dead are would-be rescuers. Emergency teams trained in trench rescue should be contacted immediately in the event of a cave-in. http://www.cdc.gov/elcosh/docs/d0200/d000279/ilochap93.html Encyclopaedia of Occupational Health and Safety, Fourth Edition Chapter 93 - Construction Jack Mickle, Jack L. Mickle & Associates
Basic Rules of Trench RescueBasic Rules of Trench Rescue Immediately get help from units trained in trained in trench/confined space rescue Call 911 Do not enter trench Get people out of the trench
•.New York City Building Code http://10.217.254.107/NXT/gateway.dll?f=templates&fn=default.htm$vid=BldgCd2:viewBC •.CDC -Occupational Fatalities During Trenching and Excavation Work –United States, 1992-2001 www.cdc.gov/mmwr/preview/mmwrhtml/mm5315a2.htm •.CIRPC-University of Tennessee, Knoxville –An Analysis Of Fatal Events In The Construction Industry –2001 prepared for Office of Statistics –OSHA http://www.cdc.gov/elcosh/docs/d0300/d000333/d000333.pdf •. CIRPC-University of Tennessee, Knoxville –An Analysis Of Fatal Events In The Construction Industry –2000 http://www.cdc.gov/elcosh/docs/d0600/d000644/d000644.PDF •.CIRPC-University of Tennessee, Knoxville –An Analysis Of Fatal Events In The Construction Industry –1999 prepared for Office of statistics –OSHA http://www.riskworld.com/Nreports/2001/Construction/C010802.htm •. Charles Culver et all. Analysis of Construction Fatalities - The OSHA Data Base 1985-1989 http://www.osha.gov/Publications/Construction_Fatalities/Confat.pdf •.OSHA Technical Manual SECTION V: CHAPTER 2 EXCAVATIONS: HAZARD RECOGNITION IN TRENCHING AND SHORING http://www.osha.gov/dts/osta/otm/otm_v/otm_v_2.html#1 •.Larry C. Brown et all , Ohio State University Trenching And Excavation Safety Principles http://ohioline.osy.edu/aex-fact/0391.html •.J Irizarry et al . Analysis Of Safety Issues In Trenching Operations, Purdue University https://engineering.purdue.edu/CSA/publications/trenching01 •Trenches and Excavations Checklist - Taken from the "Tailgate Meetings that Work : A Guide to Effective Construction Safety Training" series http://www.cdc.gov/elcosh/docs/d0200/d000246/d000246.html BibliographyBibliography

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Excavation eschenasy

  • 2. This presentation was prepared in support of the Department of Buildings Excavation and Trench Safety Guidelines Flyer. It illustrates what, in the author’s opinion, are the most important issues related to excavation and trenching safety. This presentation, as well as the guidelines flyer, are for informational purposes only. All such work must comply with the requirements in the NYC Building Code and the relevant rules and regulations. You must also comply with all relevant federal and state laws. The presentation provides links to these as well as to other relevant Internet publications. WARNINGWARNING
  • 3. The Department of Buildings has identified excavation and trenching as areas where code compliance needs improvement. The attached flyer is being handed out to remind contractors, workers and the general public of the basic safety rules for excavation and trenching. DOB FlyerDOB Flyer
  • 4. At about the same time, OSHA published its own card intended to remind the public of the safety rules for trenches. Photo Courtesy OSHA OSHAOSHA
  • 5. Contractors Shall Comply with both OSHAContractors Shall Comply with both OSHA Regulations and the NYC Building CodeRegulations and the NYC Building Code IT’S THE LAW IT MAY SAVE YOUR LIFE IT’S GOOD ENGINEERING AND BUSINESS PRACTICE
  • 6. Trench Walls will CollapseTrench Walls will Collapse Typically, trenches are only open for a short period of time (minutes or hours). The walls of any trench will eventually collapse; it is merely a matter of time. Short-term apparent stability is a temptation for a contractor to send workers into a dangerous trench in hopes of rapid progress and financial gain. Death or serious injury can result. http://www.cdc.gov/elcosh/docs/d0200/d000279/ilochap93.html Encyclopaedia of Occupational Health and Safety, fourth Edition Chapter 93 - Construction Jack Mickle, Jack L. Mickle & Associates
  • 7. 38% Cave-in is the most common accident in Excavation & Trenching Trenching/Excavation AccidentsTrenching/Excavation Accidents J. Irizarry et al . Analysis of Safety Issues in Trenching Operations
  • 8. 37 % of all trenching accidents occur at depths less than 5 feet J Irizarry et all . Analysis of Safety Issues in Trenching Operations AccidentsAccidents vsvs. Trench Depth. Trench Depth
  • 9. Project Value Percent Cumulative 1 Under 50,000 28.51 28.51 2 50,000 - 250,000 18.81 47.38 3 250,000 - 500,000 10.35 57.73 4 500,000 - 1,000,000 8.94 66.67 MostMost FatalitiesFatalities Occur in SmallOccur in Small Construction ProjectsConstruction Projects 28 % 66.6%$1,000,000.00 $50,000.00 AN ANALYSIS OF FATAL EVENTS IN THE CONSTRUCTION INDUSTRY 2000
  • 10. Most Fatalities Occur:Most Fatalities Occur: •In trenches 5 feet to 14 feet deep •In collapses that developed extremely fast. •Additional [secondary] collapses are very common •Co-workers attempting to rescue someone can also become victims
  • 11. Analysis of Construction Fatalities - The OSHA Data Base 1985-1989
  • 12. Plan Before You Start ExcavatingPlan Before You Start Excavating Inspect the site. Collect information. List the risks. Mitigate or eliminate potential problems Establish minimum rate of inspection Have written site safety plan, including emergency procedures
  • 13. Understand Protection RequirementsUnderstand Protection Requirements Determine project requirements and conditions Understand basic soil identification Understand available protection choices – Benching – Shoring – Terms – Selection – Installation and Removal Understand effects of water
  • 14. Refer to §27-1032 of the NYC Building Code (www.NYC.gov/buildings) and OSHA’s regulations (www.osha.gov) for details on the proper protection of an excavation or trench.
  • 15. Soil Identification - GeneralSoil Identification - General •Rock •Gravel •Sand •Silt •Clay •Fill See NYC Building Code Subchapter 11 - Foundations Article 4.
  • 16. NYC Building Code and SoilNYC Building Code and Soil Classification Intended for Excavation Protection and Sheet Piling – Hard – Likely to crack or crumble – Soft sandy filled in loose soil In most cases the top layer where excavation takes place is fill. It’s worked and placed by man and has undetermined properties.
  • 17. OSHA Soil Classification SystemOSHA Soil Classification System Soil classification system means, for the purpose of this subpart, a method of categorizing soil and rock deposits in a hierarchy of Stable Rock, Type A, Type B, and Type C, in decreasing order of stability. The categories are determined based on an analysis of the properties and performance characteristics of the deposits and the environmental conditions of exposure http://www.osha.gov/Publications/Homebuilders/Homebuilders.html#subp •Stable Rock •Type A Soils •Type B Soils •Type C Soils •Layered
  • 18. Continued Visual Determination-Soil ClassVisual Determination-Soil Class Soil class by OSHA is dependent on the condition of the soil in the vicinity of the excavation. Check for: Cracked ground at top or wall of excavation. Fill [earth the was added or disturbed] Excavation soil that is exposed to vibrations from traffic or construction equipment. Poor drainage around excavation or water seepage
  • 19. Continued Manual TestsManual Tests http://www.osha.gov/Publications/Homebuilders/Homebuilders.html#subp See the NYC Building Code -Table 11-1, Unified Soil Classification & Field Identification Procedures See OSHA Plasticity Dry Strength Thumb penetration
  • 20. Safety GuidelinesSafety Guidelines Each side of an excavation or trench which is 5 feet or deeper must be protected by sheeting/bracing shoring or sloped unless it is cut from rock
  • 21. Sloping & Benching -Required ConfigurationSloping & Benching -Required Configuration
  • 22. Continued Shoring Systems SelectionShoring Systems Selection Soil type must be known Depth and width of the excavation must be known One must be familiar with the NYC Building Code Tables
  • 23. Building Code Terms for ShoringBuilding Code Terms for Shoring
  • 26. In this case, traffic exerts higher loads on walls of excavation - tables cannot be used.
  • 28. Violation Issued: Improper shoring and improper benching.
  • 29. The condition shown in the previous slide led to sidewalk collapse.
  • 30. Do not work in an excavation or trench filled with running or standing water.
  • 31. •Use of special support or shield systems approved by a registered professional engineer. •Water removal equipment, i.e. well pointing, used and monitored by a competent person. •Safety harnesses and lifelines used in conformance with 29 CFR 1926.104. •Surface water diverted away from the trench. Employees removed from the trench during rainstorms. •Trenches carefully inspected by a competent person after each rain and before employees are permitted to re-enter the trench. www.cdc.gov/elcosh/docs/d0100/d000168/d000168.html Accumulating or Standing Water Must Do’sAccumulating or Standing Water Must Do’s
  • 32. Despite significant shoring -water removal might still damage the adjoining building.
  • 33. Regularly check the walls of an excavation or trench for cracks, bulges and spalling. Check the shoring for signs of distress -- especially after a rain storm.
  • 34. •Area at the top of the trench •Trench walls •Excavated area at trench bottom •Excavation protection system Daily Inspections Should Include:Daily Inspections Should Include:
  • 35. Site Conditions Can Change RapidlySite Conditions Can Change Rapidly Weather conditions. Inspect several times each day in case of : ∗ Heavy rains and flooding ∗ Hot or Cold Temperatures ∗ Heavy Snow or Snow Melting Vibration Dewatering
  • 36. Photo Courtesy OSHA What and Where to Look?What and Where to Look?
  • 37. Tension cracks at a collapseTension cracks at a collapse
  • 38. Do not store spoil, materials or equipment along the edge of an excavation or trench.
  • 40. Excavator left for the weekend too close to the trench edge. The improperly benched excavation might collapse.
  • 41. Underground Installations - OSHAUnderground Installations - OSHA (b)(1) The estimated location of utility installations, such as sewer, telephone, fuel, electric, water lines, or any other underground installations that reasonably may be expected to be encountered during excavation work, shall be determined prior to opening an excavation. (b)(2) Utility companies or owners shall be contacted .. to locate utility installations. (b)(3) When excavation operations approach the estimated location of underground installations, the exact location of the installations shall be determined by safe and acceptable means. (b)(4) While the excavation is open, underground installations shall be protected, supported or removed as necessary to safeguard employees.
  • 42. Stability of Adjacent StructuresStability of Adjacent Structures Excavation below the base of an existing foundation is not permitted as the foundation or the excavation wall might collapse. Shoring is required when: •A controlled inspection is required. •A licensed engineer needs to specify procedure and protection. Lack of such measures is one of the major causes of recent building distress and collapse.
  • 43. Unprotected excavation next to existing building led to bearing wall collapse.
  • 44. Each open side of an excavation or trench shall have a guardrail or a solid enclosure.
  • 45. Each excavation or trench shall have a way out such as a ladder or ramp.
  • 46. Access to and exit from the trench require the : •Trenches 4 ft or more in depth should be provided with a fixed means of egress. •Spacing between ladders or other means of egress must be such that a worker will not have to travel more than 25 ft laterally to the nearest means of egress. •Ladders must be secured and extend a minimum of 36 in (0.9 m) above the landing. •Metal ladders should be used with caution, particularly when electric utilities are present. Trench Ingress and EgressTrench Ingress and Egress
  • 47. Continued Special AttentionSpecial Attention Removal of excavation support systems must be planned and usually proceed from the bottom up. Placing as well as removal of shoring or protecting systems shall be executed without inducing collapse. Must backfill together or immediately after removal of support system. Must follow specifications. All shoring members or any other protecting system shall be assembled together as per specs. Various elements of the support systems must be securely connected together and shall not be subjected to loads beyond their capacity such as those resulting from large vehicles or equipment.
  • 48. •Installation of the support system is closely coordinated with the excavation of the trench. [1541.1(d)(1)] •Workers are protected from cave-ins, structural collapse, or accidentally being hit during installation and removal of the support system. [1541.1(e)(1)(E)] • Removal of shoring or other protective systems starts at the bottom of the excavation. Members are released slowly so structural failures will be noticed. [1541.1(e)(1)(E)] •Backfilling progresses with the removal of support systems from excavations. [1541.1(e)(1)(F)] Trenches and Excavations Checklist - http://www.cdc.gov/elcosh/docs/d0200/d000246/d000246.html Special AttentionSpecial Attention
  • 49. Trench RescueTrench Rescue Often, one death or severe injury in a trench is compounded by a poorly thought-out rescue attempt. The victim and rescuers may become trapped and overcome by deadly gases, fumes or lack of oxygen; drowned; or mutilated by machines or rescue ropes. With failed rescue attempts, most of the dead are would-be rescuers. Emergency teams trained in trench rescue should be contacted immediately in the event of a cave-in. http://www.cdc.gov/elcosh/docs/d0200/d000279/ilochap93.html Encyclopaedia of Occupational Health and Safety, Fourth Edition Chapter 93 - Construction Jack Mickle, Jack L. Mickle & Associates
  • 50. Basic Rules of Trench RescueBasic Rules of Trench Rescue Immediately get help from units trained in trained in trench/confined space rescue Call 911 Do not enter trench Get people out of the trench
  • 51. •.New York City Building Code http://10.217.254.107/NXT/gateway.dll?f=templates&fn=default.htm$vid=BldgCd2:viewBC •.CDC -Occupational Fatalities During Trenching and Excavation Work –United States, 1992-2001 www.cdc.gov/mmwr/preview/mmwrhtml/mm5315a2.htm •.CIRPC-University of Tennessee, Knoxville –An Analysis Of Fatal Events In The Construction Industry –2001 prepared for Office of Statistics –OSHA http://www.cdc.gov/elcosh/docs/d0300/d000333/d000333.pdf •. CIRPC-University of Tennessee, Knoxville –An Analysis Of Fatal Events In The Construction Industry –2000 http://www.cdc.gov/elcosh/docs/d0600/d000644/d000644.PDF •.CIRPC-University of Tennessee, Knoxville –An Analysis Of Fatal Events In The Construction Industry –1999 prepared for Office of statistics –OSHA http://www.riskworld.com/Nreports/2001/Construction/C010802.htm •. Charles Culver et all. Analysis of Construction Fatalities - The OSHA Data Base 1985-1989 http://www.osha.gov/Publications/Construction_Fatalities/Confat.pdf •.OSHA Technical Manual SECTION V: CHAPTER 2 EXCAVATIONS: HAZARD RECOGNITION IN TRENCHING AND SHORING http://www.osha.gov/dts/osta/otm/otm_v/otm_v_2.html#1 •.Larry C. Brown et all , Ohio State University Trenching And Excavation Safety Principles http://ohioline.osy.edu/aex-fact/0391.html •.J Irizarry et al . Analysis Of Safety Issues In Trenching Operations, Purdue University https://engineering.purdue.edu/CSA/publications/trenching01 •Trenches and Excavations Checklist - Taken from the "Tailgate Meetings that Work : A Guide to Effective Construction Safety Training" series http://www.cdc.gov/elcosh/docs/d0200/d000246/d000246.html BibliographyBibliography
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