Lesson 1: Buried Alive

Learning Objectives

In this lesson you should learn about:

Trench Cave-In Headlines

"Officials Probe Worker's Death in Excavation Cave-in"
Houston Chronicle
March 23, 1998
Summary
Local and federal officials are investigating the death of a 43 year old construction worker buried alive when the 18-foot deep trench in which he was working collapsed. The excavation was part of a sewer sanitation rehabilitation project just east of downtown Houston. Although a steel trench box was in place in the excavation, the worker was in the trench but outside of the trench box at the time of the cave-in. Co-workers on the street scrambled into the pit and frantically dug the dirt away from the face of the man, who was buried about six minutes. When firefighters arrived, they found the man conscious and were able to feed an oxygen line to him. As rescue work was in progress, a second cave-in occurred, trapping two firefighters who were trying to help. The second collapse also covered up the victim, and he died a few minutes later.
 
The president of the company that employed the worker stated that this was the first fatality in the 43-year history of the company. "We are all devastated by it," he said. "We operate extremely safely, and we pride ourselves on that."
Comment
Trench boxes or "trench shields" are designed to shield workers from collapsing soil in the event of a cave-in. The employee was killed because he was not in the box at the time of the collapse. Note also that the worker's death may have been precipitated by the efforts of the rescuers. Vertical slopes exhibit three distinct phases of failure, the first phase trapped the worker, the second one may have been encouraged by the added weight and vibrations caused by the rescuers. Many fire-fighting crews around the country are trained in excavation rescues, which are very dangerous and delicate operations.
For more headlines see article archives

What is a Trench?

OSHA defines a trench as " ...a narrow excavation (in relation to its length) made below the surface of the ground. The depth is greater than the width, but the width of a trench (measured at the bottom) is not greater than 15 feet (4.6 m)...."

Trenches are very common on construction sites, since they are necessary wherever buried utilities are constructed or repaired. They are usually required for laying water lines, sewage pipes, and telecommunication cables. Also, trenches are often required whenever a part of a building or other structure is constructed below grade.

Soil is Heavy

A cube of soil measuring 1 ft. on a side weighs at least 100 lb (more in many cases). A cubic yard of soil (3 ft. on a side) contains 27 of these, or 2700 lbs. total. This weighs about as much as a mid-sized automobile. A trench wall collapse might contain 3 to 5 cubic yards of soil, weighing from 8,000 to 14,000 lbs.

Mechanics of a Cave-In

A cave-in is a sudden collapse of the soil in a trench wall, which flows into the trench cavity. Undisturbed soil is kept in place by the horizontal and vertical forces of adjacent soil. The soil removed to create a trench, is no longer available to provide lateral support for the soil left behind in the trench wall. With no support, soil from the trench wall will eventually move downward and inward into the excavation. Once precipitated a cave-in is lightening fast. Unstable soil flows quickly like a fluid into the trench opening, exerting extremely high pressures on anything in its path. This creates a serious life-threatening hazard for workers in the trench.

Cave-In Hazards

The initial momentum of collapsing soil can knock a person down and break bones. High soil pressures can impair circulation to buried extremities and seriously injure or in time kill someone buried only to his waist. A person buried only to the knees, would have difficulty digging himself out and could loose circulation to his legs. A person submerged under only a couple of feet of soil would experience enough pressure on the chest area to prevent their lungs from expanding. Suffocation would take place within about 3 minutes. Even if the person is rescued in time, the heavy soil loads are likely to inflict serious internal injuries. A person buried in earth as high as his diaphragm, would not be able to dig himself out, and his chances of survival would be low. If the face is even partially covered, death is almost certain.

Video Demonstrations

750 Pounds of Force

Suffocation by Soil

Lesson 1- Review Questions

  1. Trench accidents occur:
    1. mostly in the southern U.S.
    2. mostly in clay soils
    3. anywhere in the U.S. in any type of soil
  2. Trench collapse occurs:
    1. over several days time
    2. very quickly - little "running time"
    3. quickly, but there is usually enough warning for workers to evacuate
  3. Trench collapse usually causes:
    1. critical injuries or death
    2. minor injuries requiring on-site first aid
    3. moderate injuries requiring a visit to the doctor
  4. How much does a cubic yard of soil weigh?
    1. 800 lbs.
    2. 8,000 lbs.
    3. as much as an automobile
  5. How can a trapped worker die if only buried up to his chest?
    1. exposure to the elements
    2. suffocation: soil pressure prevents lungs from expanding
    3. ground vibrations of construction equipment

This page was last updated on Monday, September 17, 2007