A prolonged loss of electricity supply would not only cause people to 'freeze in the dark', if it were winter, but would also cause all perishable food to rot in non-operative cold stores. If this were accompanied by a loss of diesel transport, the results would be immediately disastrous. Very few people realise how very fragile big-cities have become. They are dangerous places. This would force an almost immediate evacuation of a big city.
Battery hens depend on forced ventilation.
Without it they would all die' In any case, a cessation of oil and electricity supplies would have serious consequences in the countryside too. Most grain in Northern Europe is stored with a high moisture content having been combined in forced ventilation. If the ventilation broke down, the grain would heat and grow mouldy. Potatoes are stored in huge chilled warehouses. If the power were cut off the potatoes would sprout, or rot.