Mother of All Grease Fires (1994)

Source: Hacker News

Background

I work in the very center of Palo Alto, in a computer‑company office building that is surrounded by restaurants, hotels, a bank, an art‑supply store, and other businesses. Because our building consumes about a megawatt (1 million watts) of electricity, it is powered by a large transformer that cannot be mounted on a pole. The transformer is housed in an underground vault located in the middle of a pedestrian walkway that leads to City Hall. The vault is roughly the size of a one‑car garage, accessed by a ladder from street level, and is well ventilated because the transformer generates a lot of heat.

Incident

Patrons at a nearby restaurant began complaining of an unpleasant odor in their outdoor seating area. The Health Department investigated and determined that the smell was caused by rancid oil that had seeped into the sidewalk. Further investigation traced the source to an overflow from a nearby grating marked “City of Palo Alto Utilities.”

Investigation

The utility crew discovered that the “oil” was actually molten deep‑frying grease. The heat from the million‑watt transformer kept the grease in a liquid state, and the vault was completely filled with about 2,000 gallons of used frying grease—enough to cover the transformer entirely.

Police determined that, for many years, a nearby restaurant had been emptying its fryer into the transformer vault at closing time, mistakenly believing they were dumping it into the storm sewer (which is illegal). The transformer’s heat prevented the grease from solidifying, creating a hidden hazard that could have resulted in a massive fire had the transformer overheated.

Resolution

The building’s power was shut off, the hot grease was pumped out, the vault was washed, and the transformer was replaced. Fortunately, no one was injured.