Trench Awareness Training

For safety is not a gadget but a state of mind.  ~ Eleanor Everet

Objectives Governing Standards Anatomy of a Trench Soil Physics First arriving units

actions/ Scene management

Equipment Familiarization

Type of Trench Collapses and Recognize hazards

Objectives cont.

Understand what is required to manage a Trench Rescue Incident

Provide tools to enable the student in making safe and effective decisions during a trench rescue incident

Implement the Incident Management / Accountability System

NFPA 1670

AWARENESS Level Functions– Size-up of existing and potential conditions– Ability to call for more resources– Development & implementation of procedures

for carrying out an emergency response system

– Site Control & Scene Management– Recognition of hazards and procedures to

mitigate these hazards

Definitions A “trench”, means a narrow excavation (in relation to its length)

made below the surface of the ground. In general, the depth is greater than the width, but the width measured at the bottom is

not greater than 15 feet. WIDTH

DEPTH

”Excavation”, includes a trench

It means any man made cut, cavity, trench, or depression in an earth surface formed by the earths removal. Again, in practical terms, when a hole is more than 15 feet wide at its base, it is called specifically an excavation. Overall, an excavation is wider than it is deep.

Anatomy

How Heavy is Dirt?

Physical forces associated with collapse:– Dirt has volume

that has mass and weight

– One cubic foot of dirt weights between 85 and 125 pounds per cubic foot.

Weight of a Volkswagen

2,785 Pounds

Weight of one cubic yard of soil

2,700 Pounds

Soil Physics

Compounding the effects of gravity is hydrostatic pressure

Add the weight of water and rock, a cubic foot of dirt can be as much as 125 pounds per cu/ft

Trench Shield / Trench Box Shields are manufactured by a

number of companies and are designed to protect workers working within the confines of the shield.

Top of Trench shield / box must be at least 18 inches above trench lip.

Additionally, the shield must be designed by a Registered Professional Engineer, be in good condition, and used properly.

Shoring

Shoring is one of the most common used methods of worker protection. It is light-weight, portable and easy to install.

The manufacturer provides tabulated data with the shoring that provides the limitations, precautions, required spacing and proper use.

This photo shows an example of aluminum hydraulic shoring. Sheeting not required with use.

Accidents without cave-ins

– Most emergencies in trenches deal with something other than a collapse

– Most of the work is done after the trench has been dug

– In these cases don’t be lulled to sleep by a protected trench

– Approach identically as an open trench

What makes trenches hazardous?

Hazards Present?

90% of fatal accidents occurred in trenches less than 20’ deep

Most deaths occur in trenches 5 ft. to 10 ft. in depth and 6 ft. wide.

First Arrival Apparatus spotting

– Spot at least 100 ft. from location Create Exclusion Zones (on next slide) Size-up – accurate address of location, length, width and

depth of trench, number of victims, length of time from collapse

Call for help-Zone 3 Secure RP, job foreman, or witness to accident Safety 360 Lockout excavator; may require Police assistance When doing a recon approaching the trench from the short

end Use available ground pads (Plywood) to stand on when near

the trench, to distribute weight near trench Conduct Risk-to-benefit analysis Assess potential hazards to rescuers and patient(s)

(Atmospheric, Water, Trench etc.) Secure the utilities and or call the appropriate utility

company Place a ladder in the trench for possible self-rescue of the

victim

Trench Scene ManagementExclusion Zones

Hot Zone 0 – 100 ft.

Warm Zone 100 – 150 ft.

Cold Zone 150 – 300 ft. All are 360 degrees around incident

Equipment Familiarization

Strongbacks,Uprights, sheeting = Shoring Panels

Airshore

Speedshore

Shoring Panel

Airshore

SCBA air supply with attached regulator to a controller to operate tool.

Speedshore

Hydraulic tool: used most in industry and public works departments

Shoring Concept

Works by creating “double funnel effect”

Strong enough to prevent soil from starting to move set in four feet intervals vertically and horizontally as a general rule.

Strut pressurizes trench wall in all directions

Types of Collapses

Spoil pile slide Excavated earth too

close to the lip Heavy rain

increasing wt of pile

Slough In / Lip slide

Slough failure

The loss of part of the trench wall

Sheer Wall

Shear wall collapse section of soil that

loses it’s ability to stand

Rotational Failure

Rotational failure Scoop shaped

collapse that starts at the lip and transmits itself to the trench walls

Toe Failure

Toe failure Slough that occurs

at the bottom Found in location of

fill dirt

Bell Pier Condition

Bell pier condition Long term toe failure

on both sides

Wedge Failure

Wedge failure Occurs with

intersecting trenches, T or L Trench

Angled section of earth falling from the corner of an intersecting trench

TECHNIQUES FOR TRENCH PROTECTION

Outside Waler

Inside Waler

Inside walers are used to span a set of panels for the purpose of creating an open space

The intersecting “T” trench is a very unstable trench because not only is one wall exposed, but a section has been cut that intersects the other wall.

The “L” trench can be describe as two trenches that intersect at there ends

Deep trenches are those trenches over 10 feet but not more than 20 feet

Trench Environments

Tacoma incident w/ fatality

Trench accidents have a 112% higher fatality rate that other construction accidents

Take Home Points Create a Hot, warm and cold zone

– Hot zone 0 – 100 ft.– Warm zone 100 – 150 ft.– Cold zone 150 – 300 ft.

Size-up – accurate address of location, length, width and depth of trench, number of victims, length of time from collapse

Initiate command & Call for a Zone 3 Trench Rescue response Secure RP, job foreman, or witness to accident Identify a staging location Control traffic movement Shut down all heavy equipment operating within 300 ft. of the collapse,

including excavator. Lay ground pads near the trench Ladders for egress every 25 ft. for possible self-rescue of victims in the

trench