to
identify and remove any potential hazards.
A competent person is someone who can recognize hazards
in the area and who has authority to take quick
actions to eliminate the hazard, which may include
temporarily stopping the work.
Inspections must be performed at the start of every
shift, after a rainstorm, or whenever conditions change.
The competent person must also test the soil
in a trench.
OSHA requires at least one test by looking at the
soil and at least one test by hand.
If a person knows the soil types,
they can pick the right protective system to keep
workers safe when they're in trenches.
OSHA classifies soil in a trench as stable rock,
type A, type B, or type C soil.
Stable rock is the safest soil for a trench, type A
is the next most stable, and then type B, and
finally type C soil is the least stable.
It's important to remember that trenches can have
different types of soil based on depth and climate conditions.
The competent person can choose from different
protective systems for a trench, based on the types
of soil found.
For all trenches deeper than 5 feet deep or for
any trench that shows signs of cave-in, OSHA requires
sloping, benching, shoring, or shielding to protect
workers from cave-ins.
Let's review each of these different systems,
and then see how each one could be applied to
the cave-in incident shown earlier.
We'll look at sloping first.
Sloping protects workers by cutting back the sides of
the trench so the sides slant away from the trench.
OSHA's rules identify the degree of slope allowed
for each of the different soil types.
When trenches are less than 20 feet deep, these are
the basic maximum allowable slopes for each soil type.
Stable rock can be vertical walls, but can not be undercut.
For type A soil, OSHA requires that the walls be
sloped 9 inches out for every 1 foot of trench depth.
For type B soil, OSHA requires that the walls be
sloped 1 foot out for every 1 foot of trench depth.
For type C soil, OSHA requires that the walls be
sloped 18 inches out for every 1 foot of trench depth.
It's important to note that this kind of sloping
can only be used for trenches less than 20 feet deep,
any deeper and the protection must be designed by a
registered professional engineer.
So now, let's look at the workers in the original
scene who were stuck in the trench as it started
to cave in.
But this time, the soil has been classified as
type B, the trench has been properly sloped, and the
spoil pile is moved away from the edges of the trench.
The trench walls are not caving in and the
workers are safe while they work.
Now let's review the shoring type of protective
system for trench workers.
Shoring uses various support systems to prevent
soil and the trench walls from moving.
There are different kinds of shoring systems, but
timber and aluminum hydraulic are the two basic types.
Aluminum hydraulic cylinders are the most common
type of shoring, and they are typically installed
using spot bracing, plywood, or stacked methods.
To install the shoring correctly, you must first
determine the soil type.
The type of soil and depth and width of the trench
determine the maximum vertical and horizontal spacing
used with the members of the shoring system.
If we use our example of a 3-foot wide, 10-foot
deep, 40-foot long trench in type B soil, the
shoring system being installed would need to
include 12 strong aluminum vertical shores, with
six on each side of the trench.
These shores, also called rails, will be connected
by hydraulic cylinders every 8 feet along the
length of the trench.
A hand pump pressurizes the hydraulic cylinders
until they fit tightly within the rails.
Now that the shoring's in place, let's look again
at the workers in the trench at the beginning of
As before, the workers are laying a sewer pipe into
the bottom of a trench.
But now the shoring system prevents the trench
walls from caving in and keeps the workers safe.
Sloping and shoring are ways to protect the sides
of the trench so they don't cave in.
Now, let's talk about shielding, which is a way to
protect the workers when they'