Lightweight Building Construction Helps Prevent a Major Disaster
Twenty-five fire companies responded to a major gas line explosion that caused the total collapse of a 10,000-square-foot supermarket. All 52 of the building’s occupants miraculously escaped through the blown-out walls when the roof lifted and came to rest on the supermarket’s shelving.
A one-story, 80 X 120-foot cinder block wall structure covered by a roof assembly of lightweight roll-bar steel truss and Q decking housed a supermarket selling floor in the Davis Creek area outside of South Charleston, W.Va,
Across the street, 75 feet away, an excavation crew was working to install a storm drain. At approximately 12 noon, the crew accidentally unearthed a 3-inch gas pipeline that had been out of use for some time. The odor of gas permeated not only the work area, but began to be noticed by the 52 people in the supermarket.
After reporting the leak, the crew began a search for the shutoff valves on the pipeline. This proved fruitless as the roadway had masked over previous pipe locations. Still, the search continued and the odor in the store increased.
Unbeknown to the workmen, their heavy machinery had caused the 3-inch pipe to fracture a “T” at its terminus—a 4-inch-high pressure gas supply line delivering natural gas at 45 psi. This rupture, undetected during the incident, was located later under the parking lot of the supermarket.
Gas under pressure began leaking through the porous ground area up to the blacktop of the parking lot. The gas is believed to have spread horizontally to the excavation hole and to have found its way into the hollow cinder block of the supermarket. The gas, with its lighter than air consistency, began to fill the walls and the 10,000square-foot cockloft space formed by the lightweight truss roof construction and drop ceilings. The gas odor continued for approximately two hours.
At 1:56 p.m., witnesses heard a loud rumbling noise, followed by a sudden fiery explosion. The entire roof assembly lifted 10 to 20 feet into the air and all four walls, losing their integrity, crumbled, with the exception of part of the rear wall that leaned diagonally against a parked delivery truck. This fact was to provide additional fire control later on. The roof came down to rest on the tops of the store’s refrigeration, storeroom and shelving.
—photo by Kenny Kemp.
A second explosion, followed by heavy fire conditions, occurred seconds after the initial explosion. It was thought to have been the ignition of a now ruptured gas line in the rear of the store.
—photo by Kenny Kemp.
Arriving fire fighters from the Davis Creek Volunteer Fire Department were faced with heavy fire and smoke conditions in and around the totally collapsed structure. They positioned their pumper in close proximity to the disaster area, and a call for assistance was sent to the Charleston and South Charleston Fire Departments. Before the incident was concluded, 25 fire companies had responded with manpower, tankers and equipment.
Initially, the only water supply was hand lines supplied by a booster tank.
Approximately 3000 feet from the store, the City of South Charleston had installed a hydrant capable of supplying 150 psi. This hydrant was put there solely for the purpose of protecting a South Charleston city garage and maintenance shop located outside the South Charleston city limits.
South Charleston arrived at the hydrant and stretched 1200 feet of 3-inch hose. Charleston’s pumper completed the inline by stretching an additional 1200 feet from South Charleston to a point close enough to supply the first-in pumping engine of the David Creek department.
Drafting pools were set up toward the rear of the store and supplied by approximately seven rotating tanker trucks.
Sixteen ambulances were dispatched from Kanawha County Emergency Authority. Ten went to the scene and six stood by at a staging area set up a mile from the incident. A triage site was established approximately 100 yards from the explosion site to treat and remove any victims requiring medical attention. Injuries were suspected to be more serious than they actually were. Fire and rescue efforts were coordinated by Davis Creek Fire Chief Jack Vaness and Kanawha County Director William White.
Strategy and tactics
The fire strategy was to position water between the fire in the rear of the store and the area thought to still contain approximately 10 to 15 trapped civilians. An exposure fire problem, a 12-room house, was 30 feet from the rear of the store. A fire that immediately had communicated to a small portion of the house was rapidly controlled and extinguished. The radiant heat source was controlled and the house saved because of hand lines played on the house during fire fighting, and because a large soda delivery truck, located between the point source of the fire and the house, held up the supermarket’s collapsed lightweight wall that absorbed most of the radiant heat.
With hose lines positioned at the fire in the store, rescue efforts intensified. A command post was established and lists of the missing persons prepared.
Fire fighters worked not only to put out the blaze, but also to examine a large area of collapsed debris for life. As these efforts continued, thick clouds of black smoke rose hundreds of feet into the air as occasional small outbursts of fire from trapped pockets of gas erupted.
It was initially thought there were at least 10 victims under the debris, but all searches proved negative. All persons reported within the store had miraculously found their own way to safety through the blown down walls surrounding them. The end result was that of the 52 people located in the store during the explosion, only 19 were removed from the scene to be treated at nearby hospital facilities. Seventeen had relatively minor cuts and abrasions, a few had reported eardrum damage, and only two suffered second degree burns over 20 percent of their bodies. They too have been released.
At presstime, a hearing had been set by the National Transportation Safety Board to determine the actual causes and events surrounding this incident.
It is thought at this time that the leaking gas found its way into all the structure’s open wall spacings and cockloft. Banking down, the gas must have found one of many ignition sources, e.g., refrigeration, air conditioning, lighting, and circuits.
The secondary explosion and large fire in the rear of the store is thought to have been caused by the rupture of the store’s gas metering devices.
The store’s new noncombustible, lightweight truss construction is normally a detriment to fire fighters, causing collapse within five minutes of fire exposure. However, in this case, had it not been for this lightweight type construction inadvertently allowing for “explosion” venting of the supermarket, results would have been reversed. Heavier construction would have contained the explosion pressure and fire, causing many civilian deaths by pressure, fire and increased weight of heavier roof assembly members raining down on them. The lightweight roof not only lifted easily, providing instantaneous vertical venting for the pressure rise during the explosion, but was easily supported by the selling floor shelves, offering trapped civilians rapid exit through the blown down enclosure walls.
Photo by Gary Scott
The numerous questions surrounding this incident will be reported in a follow-up feature.