Electrical sign fire

Mar 1, 2009 by

The insured had a business located on a busy city street, not far from a freeway. To advertise to the swarm of passing potential customers, they erected a 30 foot tall sign, advertising their services. A half dozen years passed. Then the sign caught fire, and was badly damaged. GEI was called in to answer the question, “What really happened?”

Due to the size of the sign, a large crane was required to safely dismantle and lower the various sign components to the ground. Our preliminary examination was conducted ten days after the sign burned.It consisted of a visual inspection of the sign from ground level as well as electrical measurements of the sign’s circuit-breaker box. The sign’s electrical supply came from a breaker panel in the business’s main building. A 230 volt, single phase, 60 HZ circuit was sent from this panel to the local breaker box on the sign. The 230 V current from the local breaker box was sent to a step-down transformer in the sign base, lowering the voltage to 115 V, a voltage that was suitable to operate the fluorescent lamps that illuminated the sign. There were four breakers in the box and three of these breakers were connected to the sign circuit. One breaker was found in the tripped A metal panel was found lying loose on the ground next to the sign. The paint on this panel matched the paint on the sign.

The next phase of our examination was an initial aerial survey from the vantage point of a man hoist. A hot spot at the bottom of the lower tier of the sign, on the side where the fire damage was greatest, became apparent.

When the sign was lowered by crane and set onto flat bed semi trailers for transport to the storage yard, our expert was able to examine the hot spot and discovered that its position coincided with a fluorescent light ballast.

The ballast failed. It should have stopped conducting. However, it did not stop conducting. The ballast’s internal fail-safe did not work and the ballast overheated. The burn marks on the raceway indicated that it reached a very high temperature. Thus the ballast was the primary cause of the fire.

The secondary cause of the fire was examined next. Pigeon guano, feathers, nesting material, and dead pigeons covered most of the bottom surface of the sign. This indicated that pigeons had access to the sign and that the sign service company was not cleaning the sign. In both conditions, the bird access and the lack of cleaning, maintenance was below the normal standard of care for the sign maintenance industry.

The guano/nesting material mix was missing in the vicinity of the hot spot (because it had burned to ash). A mixture of guano and nesting material form a material that is rich in nitrates and carbon, i.e. a material that is akin to gunpowder. The climate at the sign site was hot and dry. It would be expected that the guano/nesting material mix would be highly inflammable.

Sign maintenance was at fault. If the inflammable deposit of pigeon guano, feathers, and nesting material was not in the sign, it is likely that the fire would not have occurred. Rather, the ballast failure would have resulted in a short in the external wiring that would have tripped the breaker, ending the incident.

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