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Secretary of Labor Thomas E. Perez
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Excavations in Construction/Trenching

In the U.S., more than 800 construction workers

die every year while on the job.

One of the most dangerous types of construction work

is trenching, which kills, on average, 40 workers

every year.

Workers can suffer death or serious injury within

minutes of being caught in a trench cave-in.

But these deaths can be prevented.

The video you are about to see shows how quickly

cave-ins lead to workers' deaths.

The video will also show what employers must do

to assure that the work can be done more safely.

Employers have a responsibility to provide a safe

workplace and required protective equipment.

You'll see that using the right type of

protection saves lives.

Please be advised.

The scenes you are about to see deal with deaths at

construction sites and might be disturbing for some people.

All scenes are based on true stories.

Five workers were putting a sewer pipe into the

bottom of a trench, with a ladder nearby

to enter the trench.

There was nothing in place to protect the workers

inside the trench if the walls collapsed.

While the workers were inside the trench,

one side began to collapse.

Two workers were able to climb out using the ladder.

But the other three workers were buried in the soil.

And unfortunately suffocated to death

from the weight of the soil.

Let's look at the events leading up to this tragic

incident and see how it could've been prevented.

Employers must follow OSHA rules to protect

workers in trenches.

However, here, the employer did not follow OSHA's rules,

which led to these workers losing their lives.

Let's go over the main points of OSHA's rules

for trenches to see how to keep workers safe.

All trenches must follow OSHA's rules.

One cubic yard of soil can weigh as much as a car,

nearly 3,000 pounds, so unless the trench

is cut entirely into stable rock, protection against

cave-ins must be used for all trenches more than 5 feet

deep or for any trench that show signs of cave-in.

Before workers can do any work in a trench,

a competent person must conduct an inspection 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

the video.

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're inside the trench.

Shielding involves using trench boxes—also known as

trench shields—or other supports to protect workers

inside a trench from collapsing soil if a cave-in occurs.

The competent person should pick a trench box that is

right for the soil type and all other site conditions.

A trench box has two large plates, which are held

apart by four horizontal cross-members.

These plates, or "shields," must be between the

sides of the trench and the work area.

The shields are strong enough to protect workers

inside from a soil collapse.

The shields can be two feet above the bottom of the

trench as long as they can support the entire depth

of the trench and there is no caving under or

behind the shield.

The top of the shield should extend at least eighteen

inches above the level of any materials that could

cave into the trench.

Trench boxes are typically used in open areas, but

they can also be used with the sloping methods

discussed earlier.

So, let's see how a trench box could have saved the

workers that we saw at the beginning of the video.

For our example, we'll assume that the workers are

in a trench with type C soil and no sloping, but

working inside a trench box.

This time, as the workers lay the sewer pipe into

the bottom of the trench, they are protected

from any possible cave-ins.

This example shows the importance of employers

following OSHA's excavation standards to ensure

that workers are provided with a safe workplace.

These types of construction deaths are preventable.

The trench cave-in prevention measures shown here

save workers' lives.

Use these protections on the job:

it could be the difference between life and death.

If you would like more information,

contact OSHA at www.osha.gov

or 1-800-321-OSHA

that's 1-800-321-6742