It was during the transition from "legacy" homes with "legacy" furniture to "modern" homes with petroleum-based furniture that fire investigation went down the tubes. Fires burned "too fast" to have been accidental. Furniture melted and left a "flammable liquid pour pattern" on the floor. And when flashover occurred, it used up all the oxygen in the room, resulting in burning on the floor, because that was the only part of the room with any air. There were lots of accidental fires "determined" to be incendiary by well-meaning but poorly informed investigators.
Fire investigators in the 50s and 60s had it much easier than fire investigators today.
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