Invisible Danger

®	March 2000

INVISIBLE DANGER

By Michael Shaw, Captain
City of San Jose Fire Department

It was an unusually windy Saturday morning, last year, the day before Easter. E30, along with the balance of a structure response, was dispatched to a reported electrical fire in an old four-story, sixty-foot-tall building located at 50 South First Street. Upon arrival, I noticed the building was of ordinary construction with masonry walls and a wood framed interior. At the time it was under complete renovation.

The old building was built in the early 1920s. It had temporary shoring and scaffolding on every floor. Each floor was about 12,000 square feet. We soon found there was no electrical power to the building other than the temporary power brought in for the renovation work. This seemed a bit odd to me because I thought I had heard something regarding an electrical fire when we were dispatched. The teletype copy I had seen indicated there was a possible electrical fire.

From the First Street side of the building, there was no indication of a fire. However, a closer look at the roof showed a small wisp of smoke, barely visible as it swirled in the wind, behind the parapet wall. It was too far away to accurately size up from the street, so we went to the roof. Located directly next door to the involved building was another old brick building similar in construction and exactly the same height. It conveniently had a fire escape to the roof with a dry standpipe. I thought to myself, "This is perfect." I could not have asked for a better place for a fire escape and a standpipe.

Iin the street about 20 feet in front of the building were the streetcar tracks that carried the light-rail vehicles for the Santa Clara Valley Transit System. Directly over the track is the wire that powers the system called the catenary. It carries 750 volts DC to run the electric motors in the streetcars. The wire prevented us from placing an aerial on the First Street side.

On the top floor we could see that the roof had been completely reconstructed. We climbed through an access hole onto the roof and went to the area where the fire was burning. We had a small fire involving the newly framed roof that was starting to take off. The wind was strong and gusting to 35 mph or higher. Fed by the wind, the fire was rapidly growing and quickly spreading. Additional alarms were quickly called to handle the potential fire in this building.

As I looked over the parapet, I could see several of the companies in the street. I ordered the fire escape to be laddered, and the crews to climb the fire escape with their lines and equipment. I also ordered the engine to hook into the standpipe so we could set up the fire attack from the roof of the building next door. I still could not believe that the fire escape and standpipe were so perfectly located. What a break! I was thrilled and thought, "This is going to be over in just a few minutes. Just as soon as they ladder that fire escape we are in business."

I could see the crew bring an aluminum ladder from an engine to the fire escape. Just as the ladder was about to be raised, it was suddenly returned to the rig and the crews entered the building. I thought to myself, "What the heck is happening here?" I was informed by radio that the fire escape was energized with electricity. I didn’t understand how it could be, but I didn’t question it. I ordered a 3-inch line brought to the roof via the inside stairs. The plans were to wye-off the 3-inch line and have two attack lines. We went back inside the building to assist with deploying that line.

Hose was pulled from the engine and extended inside. Firefighters were spread on all floors and located at each bend in the route the hose was taking. There were at least 20 firefighters, all pulling and dragging hose around corners and up stairs. The hose was singing as it rubbed the corners of the wood. Couplings were jumping and banging as they passed by. We had over 400 feet of hose to the top floor and split it into two attack lines. By now, half of the newly constructed roof was involved with fire as the wind whipped it. To the outside went a 2½-inch hoseline, knocking down the body of the fire. In a short time the fire was out and it was time for the investigator to determine a cause. Since nobody had recently worked in the area of the fire, I couldn’t imagine what might have started it.

It was determined that the cause of the fire was an electrical arc from the metal flashing covering the parapet wall. All of the metal on the building had somehow been energized with electricity, including the fire escape, metal flashings and rain gutters.

On the First Street side of the building, located in the vicinity of the second floor, was a section of metal conduit riser that ran up the outside wall 30 feet or so. It had become dislodged at the top and fell straight out toward the street, while remaining connected to the junction box on the wall at the bottom. As luck would have it, it fell across the catenary line, located 20 feet from the wall. The metal conduit, now energized with 750 volts DC of Transit System power, charged all of the metal in the building that touched it including the fire escape. Metal flashing which contacted the fire escape at roof level also became energized. The energized flashing arced, igniting the roof. The conduit riser became so hot that it burned off at the junction box and fell to the ground. Dozens of burn spots from electrical arcing were later observed around the outside of the building. About half of the buildings on the block revealed evidence of arcing as well.

Looking back, I have to wonder what the odds are of all of these circumstances occurring simultaneously: 1) A roof fire on a large commercial building; 2) A fire escape and a standpipe perfectly located to the roof next door. 3) The fire escape energized with 750 Volts DC.

Our profession presents many dangers we continually think about. However, this illustrates one of the many variables that exists. Because anything is possible, we must always remain alert!

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