Shoring Techniques Put To The Test At Trench Cave-In

September 1995 was an unusually busy "technical" rescue month for the City of Pontiac, MI, Fire Department (PFD). Within under 20 days, members responded to a confined space search/firefighting operation, a farm tractor extrication, a partial building...


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September 1995 was an unusually busy "technical" rescue month for the City of Pontiac, MI, Fire Department (PFD). Within under 20 days, members responded to a confined space search/firefighting operation, a farm tractor extrication, a partial building collapse that included a stokes basket (rope rescue) operation and an excavation cave-in rescue and recovery.

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Photo courtesy of the Pontiac Fire Department
Firefighters from Pontiac and West Bloomfield work in the rescue area.

Each job required a combination of special skills, equipment and innovative thinking. The results of these incidents included the rescue of four people and one body recovery. The cave-in operation, in particular, blended techniques learned in trench rescue training with procedures used in structural collapse stabilization.

At about 5:30 P.M. on Sept. 22, the West Bloomfield, MI, Fire Department was notified of a "cave-in" accident on Farmington Road. First-arriving companies found workers in a 13-foot-deep excavation. A large section of compact clay soil had sheared off the vertical wall of the excavation project. Working with construction company employees, the West Bloomfield firefighters removed two workers from the hole.

A third worker, however, was partially buried and crushed. Falling soil had driven him onto the large pipe that he had been welding and buried him from mid-torso down. Unprotected vertical dirt walls were on three sides of him. The distance between the two walls running perpendicular to Farmington Road was 26 feet. The wall that had sheared was adjacent to the road and, in fact, was dug right up to the curb. The wall that was parallel to the road was a sloping wall about 50 feet away.

West Bloomfield firefighters closed Farmington Road to traffic and established a pedestrian perimeter shortly after their arrival. They then requested technical rescue assistance from the Pontiac Fire Department, which maintains a Technical Rescue Squad truck and a Collapse Rescue trailer.

Concerns addressed by West Bloomfield and Pontiac fire personnel, in what was to evolve into a two-hour body recovery operation, included:

  • Scene control. General area control was established, with police help, by barring traffic, preventing civilian access and providing for media coverage from a safe distance. Rescue area control was established with access limited to assigned personnel.
  • Hazards. Utilities, such as overhead wires, underground gas, electric and water lines, as well as the presence of fuel and hazardous material containers, were all evaluated.

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Photo courtesy of the Pontiac Fire Department
A view of the trench. The victim was crushed and partially buried by the collapse.

At the time of the collapse, welding was being done within the hole. The power source for the welder was on a truck parked on Farmington Road. This unit was readily accessible and was shut off and secured. The "lip" area was protected with ground pads from the PFD collapse trailer.

Unsecured trenches and excavations are extremely dangerous areas because of their potential for collapse (or secondary collapse). Well-intending rescuers can cause soil to collapse when digging in unprotected excavations. This not only places them at risk but has the potential to further injure the people they are attempting to help.

Wall Stabilization

Shorform panels with pre-attached two-by-12-inch uprights were placed into the hole to begin the shoring operation. Because of the width of the excavation, a plan was developed to use two panels pinned back by the bucket of a backhoe already in the excavation.

This temporary bracing was planned to be used exclusively for "safety shoring" to protect shoring personnel who had entered the hole to erect a raker (diagonal) shoring system. This system consisted of the safety shoring, panels, uprights and four-by-six-inch timbers. Small void areas behind the panels were backfilled with airbags, four-by-four-inch timbers and dirt. (A trench box was requested but was not available.)

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