10Hour Construction Safety and Health Outreach Program

1
Construction Standards for Excavations
Southwest Risk Services
2
This presentation is designed to be a discussion
of the OSHA standards provide hazard
recognition awareness training ONLY!
It is the employers duty to provide SITE
SPECIFIC training to his employees and Enforce
Safety
3
Excavations

4
Why the Training?

• People die in excavations!
• See Fatal Facts
• Regulations
• 29 CFR 1926, Subpart P

5
What We Will Cover

• Regulations
• Competent Person
• Qualifications
• Responsibilities
• Hazards of Excavations

6
What We Will Cover

• Soil Classifications
• Protective Systems
• Sloping
• Shoring
• Inspections
• Emergency Response

7
Regulations

• 29 CFR 1926 Subpart P - Excavations
• Appoint Competent Person
• Soil evaluations by Competent Person
• Daily Inspections by Competent Person
• Shoring and sloping evaluations by Competent
  Person
• Stop Work Authority of Competent Person

8
Competent Person

• "Competent person" means one who is capable of
  identifying existing and predictable hazards in
  the surroundings or working conditions which are
  unsanitary, hazardous, or dangerous to employees,
  and who has authorization to take prompt
  corrective measures to eliminate them.

9
Competent Person

• Qualifications
• Knowledge of soils and soil classification
• Understands design and use of protective systems
• Ability to recognize and test hazardous
  atmospheres
• Documented training
• Prior excavation experience

10
Competent Person

• Responsibilities
• Site safety briefings on excavation safety
• Daily excavation inspections
• More frequent if conditions change (e.g.
  freeze/thaw, rain, vibration)
• Physically located at the excavation

STOP WORK AUTHORITY!!!
11
Excavation Hazards

• Hazardous atmospheres
• Water accumulation
• Adjacent structures
• Loose rock or soil
• Falls
• Cave-in

• Surface encumbrances
• Utilities
• Access/Egress
• Vehicle traffic
• Falling loads
• Mobile equipment

12
Surface Encumbrances

• Need to be removed or supported
• e.g. fencing, piping, structure, materials

13
Utilities

• Underground
• Locate prior to digging
• Certify deactivation
• Protect, support, or remove

14
Utilities

• Aboveground
• De-energize or
• Isolation from power lines

15
Access/Egress

• Note Poor housekeeping --- 1 cause of slips,
  trips and falls on construction projects
• Debris kept cleared from work areas
• Mark hazards
• Barricade or cover holes
• Egress provided-
• 25 travel distance
• ladders
• ramps
• stairs

16
Vehicle Traffic

• Traffic Control
• Traffic Safety Vests

17
Exposure to Falling Loads

• No work under loads
• Operators remain in cab

18
Mobile Equipment

• Warning system
• Barricades
• Hand signals
• Mechanical signals
• Stop logs
• Grade away from excavation

19
Hazardous Atmospheres

• Test _at_ 4 if suspected
• LEL
• Oxygen
• CO
• H2S
• Petroleum
• Other toxics

20
Ventilation

• Displace hazardous gases and vapors
• Considerations
• Heavier than air or lighter than air contaminant
• Exhausting or blowing in
• Volume/time required to lower concentrations to
  acceptable levels

21
Water Accumulation

• Protection from hazards associated with water
  accumulation
• Protection against cave-in
• Water removal (pumping)
• Run-off protection
• Consider temporary shut-off of water lines

22
Adjacent Structures

• Ensure structure stability
• Shoring
• Bracing
• Underpinning
• Or evaluation by P.E.

23
Loose Rock and Soil

• Protection of employees from loose rock or soil
• Scaling
• Protective barriers
• Placing material at least 2 from edge
• No work on slopes above workers

24
Fall Protection

• Any surface 6 feet or more above a lower level
  shall be protected by
• walkways with guardrail systems
• personal fall arrest systems
• Other options include
• warning lines systems
• safety monitoring systems

25
Cave-in

• Protection from cave-in requires a systematic
  approach including
• Soil classification
• Protective systems
• Inspection
• Employee training

An oh sh_t!
26
Soil Classification

• Soil Classification (Type A,B,or C) determines
  construction of protective system
• Sloping or benching
• Shoring
• Timber shoring
• Aluminum shoring

27
Protective Systems

• Required unless
• Excavation in stable rock
• Excavation less than 5 (4 some states) and
  examination by Competent Person determines no
  potential for cave-in

- YO!
28
Protective Systems

• Options Include
• Sloping and benching
• Shoring/sheet piling/ shielding (e.g.trench
  boxes)
• Designed by P.E. if deeper than 20

29
Simple Sloping

• Type A - 3/41
• Type B - 11
• Type C - 1½ 1

30
Benching

• Type A
• Type B
• (cohesive soil)
• Type C

NA
31
Shoring

• Based on OSHA Appendices
• Based on Manufacturer data
• Designed by a P.E.

32
Timber Shoring Installations

• Appendix C of OSHA regulations
• Requires soil classification
• Based on depth and width of trench
• Consult tables for specs on
• Cross braces
• Wales
• Uprights

33
Aluminum Shoring Installations

• Appendix D of OSHA regulations
• Requires soil classification
• Based on depth and width of trench
• Consult tables for specs on
• Hydraulic cylinders
• Wales
• Uprights

34
Shields (i.e. Trench Boxes)
35
Protective Systems

• Installation
• Securely connected
• Employees clear of area under shields during
  installation
• Installed to prevent movement
• Must protect employees while entering excavation

36
Protective Systems

• Removal
• Employees clear of area under shields during
  removal
• Shoring removed from the bottom up, SLOWLY!
• Backfill with removal

37
Excavation Inspections

• Daily Inspections of ALL excavations by Competent
  Person
• Start of shift, as needed, following rainstorms
  or other hazard-increasing event
• Possible cave-ins
• Protective system failure
• Water accumulation
• Hazardous atmospheres
• Competent person has authority to remove workers
  from the excavation

38
Excavation Rescue
39
Excavation Rescue
40
Excavation Rescue

• Initial Size-up
• Type of incident?
• Cave-in, flooding, medical, fire, spill
• Injuries?
• Number and type
• Missing personnel?
• Chemical (or sewage) exposures?
• Safety of excavation for rescuers?

41
Excavation Rescue

• Notify
• Field personnel
• HSO Emergency Coordinator
• Fire Department
• Police Department
• Emergency Medical Services (EMS)/Hospital

42
Excavation Rescue

• Stabilize cave-in
• Control flooding
• Hazardous Atmospheres?
• Ventilate
• SCBA
• Safety harness and line
• Basket stretcher

43
Excavation Rescues

• The best rescue is the one you never have to
  make!
• Practice proper procedures
• Make sure everything is safe before anybody goes
  in!

DONT ROLL THE DICE!!!
44
TENSION CRACKS.

• Tension 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.

45
SLIDING

• or sluffing may occur as a result of tension
  cracks, as illustrated below.

46
TOPPLING.

• In 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.

47
SUBSIDENCE AND BULGING.

• An 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.

48
HEAVING OR SQUEEZING.

• Bottom 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.

49
BOILING.

• 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.

50
Theory of Trench FailureTrench 3 wide 10
deep

• Active areas
• Belly may show 1st signs of slipping.
• Slip Circle Slip Plane May settle as soon as
  trench is cut.
• Spoil Pile or Equipment is over a portion of
  slip circle

51
Theory of Trench FailureTrench 3 wide 10
deep

• Trench wall failure forces
• Weight of soil causes sideways (lateral)
  pressures on walls.
• Additional surcharge loading, vibration, effects
  from previously disturbed soil, excess moisture,
  or less cohesive soils.
• Fissures may began to appear at the top of the
  trench. Any cracks are indications that trench
  sidewalls are progressing toward failure.

52
Theory of Trench FailureTrench 3 wide 10
deep

• Belly Bulges
• Vertical lateral pressures are exerting belly
  bulges.
• Surface fissures are becoming more visible.
• Newly formed fissures are opening further from
  the excavation or on the face of the trench
  sidewalls.

53
Theory of Trench FailureTrench 3 wide 10
deep

• Initial Cave-in
• Belly of the wall under spoil pile has just
  caved in. Ledges above belly may fail in first.
• Remaining material spoil pile above belly will
  cave in instantaneously.
• Slip Circle may slip.
• (Cave-in from spoil pile side, in a
• trench 6 long, 8 deep 2 wide, would weigh
  12,000) (6 Tons).

54
Theory of Trench FailureTrench 3 wide 10
deep

• Secondary Cave-ins
• Portions of other walls begin to fail.
• Both walls may continue to fall.
• Move Spoil Pile back to a minimum of 2 from
  edge of excavation.

55
Theory of Trench FailureTrench 3 wide 10
deep

• Surface Water
• Rain is flowing into surface cracks and
  fissures. Fissures may appear to heal while wet
  but they will reappear will be wider after
  drying.
• Slip Plane Slip Circle will be negatively
  affected by water in the bottom half of trench
  causing belly to slip.
• Water retained in spoil pile will create
  additional surcharge loading conditions.

56
Soil Classification

• Plasticity Test
• Directions
• Mold a moist or wet sample of soil into a ball
  attempt to roll it in a thread.
• Cohesive soils rolls, without tearing, to at
  least a 2 length of a 1/8 thread on one end.

57
Soil Classification

• SILTY SOIL
• A fine grained soil that may contain some sand
  clay. When wet, silty soil is moldable. Appears
  shiny, sticks together, somewhat. When dry,
  silty soil crushes easily to a powder or fall
  apart. Also referred to as loamy soil or
  granular silt.

58
Soil Classification
Drying Test shows the difference btwn unfissured
cohesive Soils, fissured cohesive soil, and
granular material.
59
(No Transcript)
60
(No Transcript)
61
Tabulated DataExample
62
Questions?

• Thank You!