Date: November 21, 1980
Due to improper installation, galvanic action, and ground fault, a fire was started in The Deli, a restaurant on the main floor of the MGM Grand. This room was unoccupied but due to the open plenum throughout the main casino floor, the fire and smoke were able to spread rapidly throughout the main floor and into some of the upper floors of the hotel [b]. The end result was that 85 people died, mostly from smoke and fume inhalation, and millions of dollars in damages, reconstruction, and settlements [c]. The first of the three problems was caused by a ground fault. During installation, it was assumed that all grounding was to be carried by the aluminum conduit. The conduit was not correctly connected to a receptacle box which would lead to arcing currents if there was a break anywhere along the circuit [b]. The second problem was caused by the galvanic action that occurred when the aluminum conduit came into contact with copper pipe. Galvanic action occurs when two metals come into contact for an extended period of time and they begin to corrode. Over time, one metal will corrode faster, in this case, aluminum, which caused a break in the aluminum conduit and, in turn, the grounding path [b]. The final problem was improper installation. While pulling conducting wires through a conduit, the insulation around each conductor could be degraded due to the abrasive nature of the flexible conduit that was used in some sections. Temperature changes that occur over the cycling of the current can lead to the degradation of the insulation, as well, which would allow current to transfer from the conductor to the conduit [b]. These three problems by themselves are not usually a major problem or fire hazard, but the combination of the three allowed for the ignition of the construction materials and the propagation of the fire through the building.
Other Sources: http://en.wikipedia.org/wiki/MGM_Grand_fire
Learning from Building Failures 