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.