Sirens shattered the silence of an otherwise sunny, tranquil spring day in the foothills above Tucson, Ariz. The neighbors and tradesmen working on nearby projects stopped what they were doing as fire trucks appeared on the street. The firemen were stunned by what they saw: shattered windows, splintered doors severed from their hinges, a crumpled roofline, several distraught workmen, and the acrid smell of an explosion.
The paramedics quickly entered the single-story ranch to find two injured workmen. One, face down on the debris-covered floor, was immobile and appeared severely injured. The other was dazed, lethargic, and showing signs of shock. The injured men were immediately loaded onto an ambulance and rushed to the hospital.
Patient trauma evaluation at the hospital’s emergency room revealed that the comatose carpenter had head, neck, and back injuries coupled with broken ribs and internal bleeding. The laborer demonstrated signs of shock, had shattered teeth, a broken nose, head trauma, several stitch-able cuts, and widespread impact bruising.
After the custom home construction site was secured, the accident investigation into the cause of the explosion got under way. The fire and sheriff’s departments, OSHA, the Arizona Industrial Commission, the State Compensation Fund of Arizona (workmen’s comp), and the liability insurance carriers for both the contractor and the homeowner wanted to know what had happened.
The custom home in question was nearly completed. The original design of the 4,200-square-foot project included a sunken living room 6 inches below the main floor of the slab-on-grade home. During the final two weeks of construction, the homeowner had had a change of heart and asked the builder to raise the level of the sunken living room floor to the same grade as the main floor and install ceramic tile over the entire floor area.
The general contractor, Chuck Livingston, was having a record year in his construction business. The company was busy and had been working overtime to complete projects on schedule in order to close by the quoted completion dates. This home was not different. Chuck wanted to finish this home on time and keep the owner happy. The requested change by the homeowner was a simple one, but it was going to take some time. And due to the increasing demands on his experienced tradesmen and employees, Chuck decided to delegate this structural change to a framing carpenter who was being groomed to become a finish foreman. This would be a fateful decision.
The site superintendent was shuttling between the various projects looking after last-minute details to keep things moving toward completion. Normally, during the final phase of construction, the superintendent was on site to direct, manage, and oversee every aspect of the final pieces being assembled. But this custom home company had several projects finishing up within the same two-week period. Chuck knew that he and the superintendent could not be everywhere at once. “A good manager has to delegate,” he thought. He was faced with additional work and not enough time and manpower to properly execute it.
Chuck directed the carpenter and a laborer to raise the living room floor. “Do we do it by wood frame or pouring concrete to raise the sunken floor?” the framing carpenter asked. “I don’t care. You can decide that,” replied Chuck. “But if it were me, I’d be considering the simplest, cleanest, and fastest method. Remember, we’ve got lots of trades that need to be in and around that living room to finish their portions of work, and concrete might be messy.” In hindsight, this was another fateful decision.
The framing carpenter elected to frame the floor, sheath it with dual plywood layers, and cover it with cement board to raise it to the same level as the adjacent floor to accommodate the tile flooring. He and the laborer began their work by installing 2×4 sleepers at 16 inches on-center with 2×4 blocking every 48 inches, and a 2×4 perimeter frame as a subfloor. The framework was thoroughly glued to the concrete-slab floor with construction adhesive. The subfloor was immediately covered with a plywood layer that was also glued down with adhesive and then pneumatically nailed to the subframe. The crew wanted to get the floor completed before lunch. The weather in Tucson was typical for that time of year—sunny, dry, and more than 90 degrees.
The two-person crew immediately laid down another layer of plywood perpendicular to the first layer. This was being installed by sandwiching construction adhesive between the plywood layers and then gun nailing the second layer of plywood through the lower plywood layer into the 2×4 subfloor framing with 16d nails. (No. 8 ring shank nails probably would have been a better choice.) The second layer of plywood was completed except for the last piece. The carpenter caulked on a generous layer of construction adhesive and then placed the plywood onto the surface and began nailing.
KABLOOM! The explosion caused an immediate, massive air evacuation which blew the glazing out of windows and doors out of the jambs. The carpenter operating the nail gun was on his hands and knees while nailing and was blown up spread-eagled and horizontal into the 12-foot-high ceiling. The laborer was standing upright and walking at the moment before the explosion and was blown into a wall with such force that it left a full body outline indentation in the drywall.
