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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.
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.
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
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
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
Rotational Failure
Rotational failure Scoop shaped
collapse that starts at the lip and transmits itself to the trench walls
Wedge Failure
Wedge failure Occurs with
intersecting trenches, T or L Trench
Angled section of earth falling from the corner of an intersecting trench
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.
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
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