Ihab Saad – Excavations
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AI: Transcript ©
Music.
Welcome to another safety class, and today we're going to start
talking about subpart p, which is excavations. Definitely.
Excavations take place on most construction sites, and this is
one of the most hazardous areas, and that's why OSHA has designated
excavations as one of the focus four areas of inspections which
has the hazard of cabing ins or being
stranded in a ditch, for example, with the size of the ditch
collapsing and so on, so caught in between, which is one of the focus
four applies particularly to excavations and ditches. So today,
we're going to learn about what are the safe practices when doing
excavation, and what are the different types of soils that
we're going to be exposed to, and what kind of precautions have to
be taken with these different types of soils.
Some of the most frequently cited violations when it comes to
excavation are the protection from cave ins, which is the focus of
the of the issue here, means of egress provided, which is how to
get out of the trench in case cave ins start to happen. Daily
inspections by a competent person. We're gonna learn what's a
competent person, and why do we have to perform daily inspections?
Because weather conditions might change, there might be freezing
and flowing, or there might be some rain which would loosen the
soil and make it more susceptible to cave ins and collapse
protection from things falling into the excavation. If you have
equipment at the side of the excavation, or if you have labor
standing at the edge of the excavation. There's a Fall issue
here, and a competent person inspection employees removed from
hazard. Again, these are the most frequently cited issues when it
comes to excavation, and we can see these in our code book.
First of all, a quick refresher on what you have learned in your
soils class, or what you're going to learn in the soils class,
to think to know exactly what's the magnitude of hazard when it
comes to excavation. The density of dry soil is 85 pounds per cubic
foot. Once it gets wet with water filling the voids of that soil, it
becomes heavier, so it becomes the weight becomes around 120 pounds
per cubic foot. So if you are standing in a trench that's 10
foot deep, a 10 foot column of dirt could weigh up to 1200
pounds. So imagine if 1200 pounds collapse on a person that can
easily kill that person. That's why the big hazard when it comes
to excavation.
So how do these cave ends happen? Basically, the hazard is
unsupported. Excavations can slide into the hole. There's going to be
lack of friction. So there's these are going to slide the layers of
the soil are going to slide on top of another layer, and it's going
to fill that void. So this is basically what's going to be the
big hazard there.
Another hazard is what's called boiling water, rising up or
boiling from the bottom of the trench, which can undermine the
stability of the surrounding soil. Again, if you have granular soil,
like sandy soil, for example, with upward water pressure, that can
definitely cause that boiling and can cause the collapse of that
soil. That's another big hazard. That's why water in ditches or in
excavation is a very risky issue. We're going to talk about that
little bit later.
The third hazard is heaving, which is a downward pressure of
adjoining soil which pushes the trench bottom upwards. So the
weight of the wet soil masses, basically pushes the bottom
upwards, and that causes also a collapse, and this particularly
happens in wet clay soil, where you have the particles very close
together, and they're going to form lumps, and that can cause
this heaving.
So today we're going to talk about a competent person. What is a
competent person? OSHA has three definitions. In fact, it has a
definition for something called an authorized person, a qualified
person and a competent person. And I'm gonna read from the OSHA
definition here, an authorized person is a person who is
authorized by the employer to perform a task. So any laborer,
for example, working inside The Trench, in this case, is going to
be an authorized person because they have been authorized to work
inside the trench. However, there's another layer, which is
called a qualified person. A qualified person is a person who
has the knowledge to perform that task through education, schooling,
training or experience. So that's a higher level than authorized
person. And then the highest level is going to be the competent
person, which is going to be, by the way, and a qualified person
working a trench.
Be authorized as well. Now, a competent person is going to be
qualified and authorized at the same time, but a little bit more
so a competent person is a person who is qualified and authorized to
perform the task. And a competent person must have, and this is the
most important part here, must have the ability to identify
hazardous conditions and have the authority to take action to
maintain this the
safe workplace, or to prompt the corrective measures. So the two
major conditions for a competent person, above and beyond being
qualified and being authorized is they can identify the hazard, and
they have the authority to take prompt corrective measures
when it comes to an excavation competent person, and later on, by
the way, we're going to see in other different trades, when it
comes to safety, a competent person in excavation might not be
a competent person in electrical for example. So each trade, each
discipline, has its own competency level and its own competency
training. So a competent person in excavation is trained in soils,
recognizing the different types of soil and being able to analyze
that soil in protective systems. What kind of protective systems
are we going to use? Are we going to use benching? Are we going to
use sloping are we going to use trench boxes? What are different
types and what's the proper use, how to use them properly. Hazard
recognition, including hazardous atmospheres, especially when you
dig again, when you work inside trenches, you might have some
gasses, for example, methane, for example, or something like that,
that might be toxic for especially with the lung exposure. So again,
hazard recognition is definitely a skill needed in a competent person
knows when to call a PE for help. PE stands for professional
engineer. Usually it's going to be geotechnical engineer, or an
engineer specialized in soil analysis and soil design and
things like that, especially if the excavation is going to exceed
20 feet. In this case, you must have a certification from a PE to
allow you to work inside that trench so knows when to call a PE
for help if the soil conditions change, if we fear that there
might be some cave in or might cause some collapse, then we have
to call a PE to suggest a corrective action and knowledge of
subpart p, which is What we're talking about here, which is
soils, or excavations. Through soils,
we have to inspect equipment daily by a competent person. Equipment
might be something like a trench box, for example, which is going
to be used to support the size of the excavation. We're going to
talk about that a little bit later, so you're going to inspect
several times prior to work starting because again overnight,
there might be some conditions that changed the site specifics as
needed throughout the shift. Again, if you had heavy rain or
heavy snow during the day, then that might change the conditions
as well after rainstorms and after other hazards, hazard increasing
events, if, for example, there was a minor earthquake or a tremor
that might destabilize the soil, if there were heavy equipment
passing by that might destabilize the soil. All of these are
different conditions that require an additional inspection by a
competent person.
So some of the hazards related to excavation include surface
encumbrances, existing buildings, equipment, spoils or piles of soil
resulting from other excavation, things like that, underground
utilities. Of course, when we excavate through a site, we might
face older utility pipes or cables or conduits or something like
that. So these, some of these cables might be still live. Some
of these water pipes might be covered in asbestos, for example,
which is now a hazardous material. So we have to recognize all of
these spoiled piles again, resulting from previous
excavation. As we said, operating equipment too close to trench,
which might destabilize that trench. If you have heavy
equipment operating close by, they might destabilize it, access and
egress to and from the trench. How are we going to get to the bottom
of the trench, and how are we going to get out if we need to get
to or when we need to get to, there are going to be, for
example, slopes, or there are going to be ladders that enable us
to do so. Excavating near operating roads where you have
constant traffic, and that constant traffic, again with the
vibrations, is going to cause destabilization to the soil. And
watch the load, and stand away again if you're operating
equipment close by, watch the load from that equipment, because the
load is transferred in a
sloping line, as you can learn through soils. So stand away a
certain distance to try to avoid the debilitation of the soil,
hazardous atmospheres, so maybe in some cases.
If someone is working inside The Trench, you're going to provide a
lifeline, which is a form of personal protective equipment, so
even if that person loses consciousness, then you can pull
them out of that trench. Water in the ditch. As we mentioned,
always, water in the ditch is a very hazardous issue, especially
if you're going to be operating electrical equipment inside that
which as well, water and electricity are always a bad
combination. Fall Protection from the people outside of that trench.
They might fall in the trench, cave in protection. We're going to
talk about different types of soil. We classify them under OSHA
standards as type A, type B and type C. We're going to talk about
these in more details, allowable side slopes. We're going to learn
about these and the use of trench boxes. How should they be
installed? We're going to talk about that as well as we just
mentioned, deep excavations require a PE design was the
definition of a deep excavation, any excavation 20 feet or more,
protective systems,
if not installed properly, that might cause a hazard by itself, so
they have to be installed in the proper way.
Surface encumbrances include telephone, utility poles,
sidewalks, buildings, roadways, etc. They must be supported or
removed if they pose a hazard to employees. It happens sometimes
when you excavate, especially for mass excavation and deep
excavation, that you might find that the adjacent buildings or
structures are starting to crack or tilt or even in except
excessive cases, collapse. Why? Because the stress distribution
goes in something called the stress bulb, which goes as a at a
something like a 45 degree angle. So even if you're not digging
directly underneath the building, the stress coming from the
foundations of the building exists in the soil that you have removed.
So by removing that soil, this building, the load from the
building is not distributed properly anymore, so that causes
the building to lean or even to collapse. So this is definitely a
danger. That's why you have to support the sides of the
excavation to carry the load from the adjacent buildings.
Structures must be supported if near the excavation and
excavations must not undermine sidewalks unless properly
supported. So we're going to provide the proper support,
whether it's in the form of sheet piles, for example, that's one of
the common ways of supporting the excavation,
undercutting existing foundations. Do not excavate below existing
footings of or of structures, unless either a support system has
been provided, or excavation is in stable rock where the load
distribution is vertical, or you have a PE professional engineer
approving that excavation, because they would know exactly how the
stress is distributed and whether it's safe or unsafe to excavate
under these foundations.
In case of underground utilities, you must locate all underground
utilities. They might exist from existing maps that you might find
them through existing maps, old maps of that site, or you call the
utility company if they have any knowledge about these, the routes
of these different cables, pipes, etc. So prior to any excavation,
you have to locate the underground utilities, and the underground
utilities must be protected, either supported, removed or
guarded while the excavation is open, if they are still active, so
that they would not interfere with the excavation operations.
Call before you leave. There's usually a an 800 number. In case
you are doubting whether there are, there are utilities or not,
call that number and they're gonna give you some
some information. So contact utility company locator prior to
excavating if no response within 24 hours, if you don't get an
immediate response from them, or if they cannot establish utility
location, if they don't have existing maps, then the employer
may proceed with caution, because you may find you may hit a cable,
especially if it's a live cable that can cause electro fusion.
Employer must use detection equipment or other acceptable
means used to locate utilities. Now we have a new technology,
relatively new. It's been around for the past maybe 10 years or so,
which is called GPR. GPR stands for ground penetrating radar that
enables you by sending radar waves, ultrasound waves, it
enables you to draw a 3d to get a 3d view of what's embedded
underneath your soil before digging. So it would show you
there are pipes or there are cables, and what are their
directions and what are their volumes, etc. So you'd know before
excavation where these exist, and you can either avoid them or
deactivate them before the excavation.
It.
Loose material is always a hazard, so protect workers from loose
material that may fall from the excavation phase. How do you do
that? Again, we're going to talk about either sloping or benching,
and what is the safe distance to keep away from the edge of the
excavation and the use of trench boxes as well.
So spoil piles must be at least two feet from the excavation and
or use retaining devices to prevent material from rolling into
excavation. Again. One of these retaining devices is what's called
sheet piles. In case you haven't seen sheet piles, they are
something like a C section, steel
element that's driven vertically in the soil, and that's going to
take the lateral load of that soil so that the excavation doesn't
cave in, and that's usually used in deep excavation. Keep equipment
away from the edge of excavation, because, again, if they get too
close to the side, they might destabilize the soil and fall into
that trench. So the minimum distance is going to be two feet.
And here's a graph showing, for example, if this is a backhoe or
an excavator at the edge of the excavation, the spoiled pile must
be at least two feet from the edge, and material storage and
equipment must be at least two feet from the edge. So the minimum
safe distance is going to be two feet from the top of the edge of
the excavation, as you can see here. Now we have we can see that
it's sloped, and that sloping follows what's called the angle of
repose of the soil, which is a natural angle that the soil forms,
if left naturally, without any external support, that would be a
safe way to support that soil.
Operating equipment, too close hazard of operating equipment too
close to excavations. You have to watch for vibrations, clear view
to the rear, especially if that equipment is backing up. So if
it's backing up, you must have someone a monitor, or you have you
must have some mirrors, or any way to know whether you're too close
to the edge of the excavation or not. And the moisture content of
the soil, again, that can change the characteristics of the soil,
making it more collapsible. So use barricades or other warning
systems. Either you're gonna have cones or barricades, or you're
gonna have a flagger, someone with a flag who's going to notify the
equipment operator stop. You're getting too close to the edge of
the excavation,
access and egress. Remember these numbers here. Trenches four feet
or deeper, must have a means of egress, ladders, stairways, ramps
or others.
Travel distance, the maximum travel distance that the person
inside the ditch or the trench has to move to get out of the trench
to get to an egress or access means like a ladder is 25 feet, no
more than 25 feet. Quick question here, if we have a trench that's
49 feet long,
okay, how many ladders do we need for that trench? Think for a
second. How many ladders? Remember the maximum distance is 25 feet.
So the trench is 49 feet long. How many ladders do we need? Some of
you may have said two. Some of you may have said three. The correct
answer is one. Why is it one? If you locate that ladder in exactly
in the middle, from the farthest point on either side, the distance
is going to be 24 and a half feet, which satisfies the code.
You would like maybe to have some redundancy so that people are not
rushing to get out of the trench. So you may say, Okay, I'm going to
install two but by the code, you're going to be fine. You're
not going to be violated if you install only one ladder for that
49 foot trench. But remember, the maximum horizontal distance that
people have to travel is 25 feet.
So the two numbers that you have to remember from the slides is for
trenches 44 feet or deeper. If the trench is less than four feet, you
don't need that, because they can jump, jump over the side of the
trench, and the 25 feet the horizontal distance.
When it comes to loads, stand away from overhead loads, whether they
are buckets, clamshells or other from equipment excavating that
soil, the haul truck operators may remain in the cab for overhead
protection during loading. So if they are in the cab, they are
already protected by roof of that cab stand away from vehicles being
loaded, because, again, sometimes the operator might not pay
attention, and a person might get hit by that equipment.
Hazardous atmospheres. Check excavation for hazardous
atmospheres mesh.