Rescue Operations for Trench Collapse - Part 1

In the past, workers and would-be rescuers have become caught and, in some cases, killed needlessly in trenches that have collapsed suddenly, and with little to no warning. It has become commonplace that the public relies a great deal on the local...


In the past, workers and would-be rescuers have become caught and, in some cases, killed needlessly in trenches that have collapsed suddenly, and with little to no warning.

It has become commonplace that the public relies a great deal on the local emergency services to handle these incidents. With that in mind, this month we prepare a safe and efficient response.

A trench can be defined as a temporary excavation in which the length of the bottom of the trench exceeds the width of the floor, and the depth of the trench is greater than the width of the floor.

For ease of nomenclature, many teams identify an excavation as a hole where the floor's width is much greater than the actual depth of the trench. While there are differences with each, both can be very dangerous situations to deal with.

Trenches are made up of five main parts -- the lip, or the top two feet of the wall; the belly, or center of the wall; the toe, or bottom two feet of the wall; the wall, which is comprised of the lip, belly, and toe; and the floor, also known as the base of the trench.

It is important to identify the parts of the trench during the incident, as each part's involvement in the collapse can offer various problems with dealing with the stability of the trench (see Photo 1).

There are many reasons that trenches are dug, including storm drains, sanitary lines, utility services and repair, and roadway renovation and repair. While their purpose will vary, there are some safety standards that have to be addressed while the trench is open:

  • Any excavation or trench greater than five feet in depth must be shored.
  • Excavation of a material to a level no greater than two feet below the bottom of the support system will be permitted.
  • Excavated material (also known as the spoil pile) shall not be piled any closer than two feet of the lip of the trench ( Photo 2).
  • Personnel shall be protected from the hazards of cave-in while entering, working in, and exiting the trench (Photo 3).
  • Personnel are not permitted in shields or trench boxes while they are being installed, removed, or moved vertically.
  • In trenches less than five feet, shoring may be required if examination of the hole by a competent person suggests a potential collapse situation; vibration from road traffic or machinery can cause a cave-in; the trench has been open for an extended period of time (24 hours); or the trench runs parallel within two feet of a roadway or second open trench.

For a complete list of regulations regarding trenches, familiarize yourself with OSHA Regulations regarding trenches, mainly 1926.650; 1926.651; 1926.652; 1926, subpart P, appendices A, B, C, D, and F. Print out copies of these regulations and carry them on your apparatus; they make great reference materials.

When dealing with trenches, it is important to identify the type of soil involved in the incident to assist in determining the equipment needed to safely shore the trench. OSHA has defined four soil categories:

Stable rock is a natural solid material that can be excavated, but it will remain somewhat intact when exposed to the elements. It has the ability to sustain vertical walls up to 90 degrees. This type of material usually requires the aid of a blasting agent to assist in digging in these areas.

The next soils that provide the most stability are referred to as Class A Soils. These soils have an unconfined compressive strength (the load per unit area {square foot} at which a soil will fail under compression load) of at least 1.5 tons per square foot. Examples of these types would include strong clay that has not been dried out, cemented soils, hardpan soils, and clay loam.

Class B Soils provide a lower level of stability. These soils have an unconfined compressive strength of .5 to 1.5 tons per square foot. It is not uncommon for water to be seeping from the trench walls in this type of soil. These include weak clay soils, dried out unstable rock, previously disturbed soil and granular cohesive soils.

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