History: Great Smog Of '52, London, England, United Kingdom

In the inner London suburbs and away from town centres there was no disturbance by moving traffic to thin out the dense fog in the back streets. The result was that visibility could be down to a metre or so in the daytime. Walking out of doors became a matter of shuffling one’s feet to feel for road kerbs, etc. This was made even worse at night because each back street lamp at the time was fitted with an incandescent light-bulb which gave no penetrating light onto the pavement for pedestrians to see their feet, or even the lamp post. Fog-penetrating fluorescent lamps did not become widely available until later on in the Fifties. ‘Smog masks’ were worn by those who were able to purchase them from chemists.
Near railway lines, on which 'fog working' was implemented, loud explosions similar to the report of a shotgun were a common feature. These explosions were made by 'detonators', a form of large percussion cap placed on the track and activated by the wheels of trains. These were placed by certain signals to provide an audible warning to match the visual indication provided by the signal for the driver.