Transcript Document 7468518

Module 14
Excavations
1
Objectives
• After this module you should be able to
– identify the most common excavation
hazards
– take the steps necessary to avoid those
hazards
2
Safety Facts
• As many as 400 workers die and another 4000
injured as a result of cave-ins each year
• Most deaths occur in trenches 5-14 feet deep
• Cave-ins cause death by: suffocation, crushing,
loss of circulation, falling objects
• 1 cubic foot of soil can weigh up to 140 lbs
• 1 cubic yard of soil can weigh up to 3000 lbs
3
Excavation Hazards
•
•
•
•
•
•
Cave-in of a trench
Contacting underground utilities
Getting struck by falling objects
Falling into an excavation
Hazardous atmospheres
Equipment rolling into excavations
4
Competent Person
• Every excavation job must have one
• This person must be trained on and
knowledgeable in
– soils classification
– the use of protective systems
– the requirements of the OSHA standards
• This person must be able to identify
hazards and immediately eliminate them
• Enter excavations only after their approval
5
competent persons must have the
authority to take prompt corrective action
6
this 6’ deep vertical-sided trench is
dangerous because it is not protected
Corrective Actions: never enter a
trench like this; notify your supervisor
7
What is a Cave-In?
• The separation of a mass of soil or rock
material from the side of an excavation
and its sudden movement into the
excavation either by falling or sliding that
could entrap, bury, or otherwise injure
and immobilize a worker
8
this worker is being exposed to a life threatening situation,
an excavation with no cave-in protection
Corrective Action: never enter a trench unless it is less than 5’ deep
and you get permission from your supervisor or it has cave-in
protection
9
Shielding
10
The Theory of Shielding
• Shielding does not actually prevent a
cave-in
• Trench shields and boxes, if installed
correctly, are designed to protect workers
from the forces of a cave-in
• In order for the shield to do its job, the
worker must stay within the protection of
the shield even when entering and exiting
11
this trench is not shielded to the trench bottom
properly; these workers are still at risk for a cave-in
Corrective Action: shield the trench
to no more than 2’ from the bottom
12
the same shield is missing
struts/crossbraces
Corrective Action: always install manufactured
shielding according to the manufacturer’s directions
13
this incomplete installation provides little if any protection;
in fact, the panels themselves can become a crushing hazard
Corrective Actions: always install manufactured cave-in
protection according to the manufacture; never skip steps 14
these workers have left the protection of their
trench box; a cave-in could happen at any moment
Corrective Action: never work unprotected, cave-ins
can happen anytime without warning
15
Shoring
16
The Theory of Shoring
• Shoring prevents cave-ins
• Trench shoring, if designed and installed
correctly, counteracts the force of a cavein
• In order for the shoring to do its job, the
worker must stay within the protection of
the shoring even when entering and
exiting
17
make-shift, improperly designed shoring does
little other then provide a false sense of
security
Corrective Action: manufactured shoring should be used;
install the shoring according to the manufacturer
18
19
manufactured aluminum shoring does little
good either when improperly installed
20
Sloping
21
The Theory of Sloping
• Sloping prevents cave-ins
• Sloping, if done correctly, removes the risk
of cave-ins by sloping the soil of the
trench back from the trench bottom
22
this is a good example of a properly sloped excavation
providing a safe workplace free from cave-in hazards
23
this is a good example of a properly sloped excavation
providing a safe workplace free from cave-in hazards
24
this worker is able to work
without the fear of a cave-in
25
Ramps, Ladders, and Stairs
26
the worker in this trench has no safe means of exit
Corrective Action: for trenches 4’ deep or greater, install a ramp,
ladder, or stairs no less than every 25’ from a worker in the trench
27
Additional Concerns
•
•
•
•
•
•
Underground utilities
Overhead hazards
Mobile equipment
Walkways
Water in excavations
Hazardous atmospheres
28
striking underground utilities can be deadly
this worker has used the one-call system to locate utilities; also, he is
using safe and acceptable means to find the exact location of the utility
29
this worker is at risk of being struck by falling rocks and
excavated materials, in particular this soil spoil is too close
Corrective Action: keep excavated material (spoil)
at least 2’ from the edge of the excavation
30
overhead hazards can also be the
tools and materials workers use
Corrective Action: keep tools materials and other
project related items at least 2 feet from the edge
31
when mobile equipment is operated adjacent to an excavation, the operator
must have a clear and direct view of the edge of the excavation, or…
… a warning system shall be utilized such as barricades, stop logs, or hand or
mechanical signals; if possible, the grade should be away from the excavation
32
using this method to cross an
excavation can result in a serious fall
Corrective Action: construct a proper and safe walkway
33
this is an example of a proper walkway
walkways or bridges must have a safety factor of 4, have a
minimum clear width of 20”, be fitted with standard rails, and
extend a minimum of 24” past the surface edge of the trench
34
the presence of water usually means soil that is unstable
35
excavations must be kept as water free as possible
Corrective Actions: select, inspect, and use water removal equipment
correctly; consider such things as air-quality and personal health issues
36
with the water pump running, a possible
carbon monoxide exposure now exists
excavations greater than 4 feet in depth must be
evaluated for oxygen deficiency, flammability, and toxicity
37
these workers installed a high
exhaust pipe to prevent asphyxiation
38
compressed gas cylinders are
not to be brought into trenches
39
trying to keep as many air contaminants
as possible above grade is a good idea
40
Case Study
• A crew was installing conduit in an 8’ deep
by 2’ wide trench. The equipment
operator had gone into the company
trailer to check blueprints when another
worker informed him of a trench collapse.
41
Applicable Standards
• 1926 Subpart P Excavations
42
Your Employer is Responsible For
• Preplanning the work
• Protecting you from cave-ins
• Inspecting the excavation at least daily
and throughout the shift as needed
• Taking prompt corrective action when
needed
43
Your Employer is Responsible For
• Making sure a ladder is within 25’ of your
work area when deeper than 4’
• Ensuring that excavated dirt, rocks, and
other materials are kept back 2’ from the
excavation’s edge
• Testing the air in areas suspect to
atmospheric hazards
• Responding to and correcting hazards
pointed out by you, the worker
44
You are Responsible For
• Working defensively
• Following you company’s excavation and
trenching safety rules
• Correcting the hazards you are able to
correct
• Reporting to your supervisor the hazards
you are unable to correct
45
Always Remember
• Never enter a vertical-sided trench unless
it is less then 5’ deep and you get
permission from your supervisor
• Never enter a trench unless it is laid back,
shielded, boxed, or in solid rock
• If a trench box is used, never leave its
protection while in the trench
46
Memory Check
1. How many feet must the excavated soil,
your tools, and other supplies be kept
back from the excavation’s edge?
a.
b.
c.
d.
1 foot
2 feet
7.5 feet
25 feet
47
Memory Check
2. At what depth must a ladder, ramp, steps
or runway be present for quick worker
exit?
a.
b.
c.
d.
4 feet
5 feet
10 feet
it is never required
48
Memory Check
3. What is the greatest hazard facing a
worker while working in a trench?
a.
b.
c.
d.
hazardous atmospheres
falls
cave-ins
falling objects
49
Memory Check
4. Unless a competent person indicates that
there is a potential for a cave-in, at what
depth is a protective system required for
a trench?
a.
b.
c.
d.
2 feet
4 feet
5 feet
10 feet
50