Indoor tempura frying was prohibited in Edo because the oil posed a fire hazard.
Tempura became popular in Edo-period Japan through outdoor food stalls, where cooks fried seafood and vegetables in oil and served them immediately. The restriction on indoor frying reflected the severe danger of open flames and hot oil in Edo’s densely built neighborhoods, where houses were largely made of wood and paper.
Fires were a recurring urban catastrophe in Edo. Once a blaze began, combustible construction and tightly packed buildings allowed it to spread rapidly. Keeping deep-frying outdoors reduced the risk to homes and helped shape tempura’s identity as fast, freshly cooked street food. It was often skewered and eaten at the stall with dipping sauce.
This history is also why tempura is associated with Edo-style cuisine, alongside foods such as soba and sushi. The rule did not mean Japanese people never fried food indoors anywhere; it describes Edo’s specific urban conditions and the hazards of oil-based cooking there. The other choices—noise, poison, and flooding—do not explain the restriction.