Inspection Detail

Inspection: 311396873 - A.W. Oakes And Son Incorporated

Inspection Information - Office: Milwaukee Area Office

Investigation Summary

At approximately 8:45 a.m. on December 19, 2007, Employee #1 was installing 8 in. sewer pipe at the bottom of an approximately 20 ft deep trench. Two 10 ft tall by 20 ft long trench boxes, with 44 in. spreaders, were in use. The initial excavation was 20 ft deep, but an excavator using a 32 in. shovel had then dug between the trench boxes to a depth of approximately 22 ft. The result was that the trench boxes sat on two "shelves," each approximately 2 to 3 ft in height. A section of soil, approximately 18 in. wide by 2 to 3 ft deep by 3 ft long, caved into the trench from the 3 ft high shelf on which the trench boxes were positioned. The dirt struck Employee #1 on the back of his legs, knocking him down to his knees. The coworker acting as top man saw the cave-in and alerted the excavator operator, the foreman, and the loader operator. The coworker and the loader operator climbed down into the trench and began shoveling dirt off Employee #1. As they did this, a second cave-in occurred, coming from the same area. The dirt flowed from under the trench box, covering Employee #1 over the back of his legs. The two coworkers continued to shovel for another five minutes and had nearly cleared enough soil to free him when a third substantial collapse occurred, coming from under the trench box and from around the front of the east end of the trench boxes. This collapse engulfed Employee #1 up to his waist and knocked down the coworker who had witnessed the first cave-in, covering the coworker's legs in soil, and trapping him as well. The foreman was now also down in the trench, shoveling dirt off the coworker. He was eventually able to pull himself free of the collapsed soil and then left the trench, exhausted from shoveling. Rescue personnel from the Sommers Fire Department arrived at the site and took over rescue operations. A fourth cave-in occurred that replaced the soil previously removed. The Summers Fire Department called in the SRT Units from Lake County, IL, for assistance. During the rescue attempt, which lasted over an hour, soil continued to flow into the trench from beneath the trench box on the north side and from around the front (east) side of the open-ended trench box. No protective shielding was in place east of the trench box. The soil was sloped from about the 15 ft depth level back up to the excavator position, which was about 15 ft to the east. At approximately 10:30 a.m., a significant collapse occurred that fully engulfed Employee #1; he died of mechanical asphyxiation. In a preliminary assessment of the protective measures taken, the top of Employee #1's head was found to be 23 ft below the top of the trench box. His knees were measured at approximately 25 ft from the top of the trench box. Tabulated data provided on the trench boxes indicated that they could be used up to a depth of 35 ft for class A soil, 22 ft for class B soil, and 17 ft for class C soil. Preliminary soil classification performed in the field identified the soil as class C. Clay soil comprised approximately the top 8 ft, with sand (a class C soil) comprising the bottom layer. Clay soil located over a C sand soil was classified as a class C soil. Soil samples were taken from three different locations, including soil excavated during the recovery. The recovery effort took approximately 13 hours. The top man later stated that he saw the fissure occur and tried to warn Employee #1 of the pending cave-in.

Keywords: TRENCH BOX, ASPHYXIATED, WORK RULES, CONSTRUCTION, TRENCH, UNSTABLE SURFACE, SHORING, UNSTABLE SOIL, SLOPING, BURIED