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Sixty-five years ago today a ‘smog’ formed over London that would last five days and claim at least 4,000 lives.

London was used to its thick ‘pea-souper’ fogs, which could reduce visibility to just a few feet and bring the city to a near-standstill, but ‘smog’ – a combination of smoke and fog – was far more dangerous.

It formed when thick, immobile fog mixed with the smoke, soot and sulphur dioxide from London’s thousands of domestic chimneys and its ‘dirty’ coal-burning heavy industries. The result was a choking and toxic cloud suffocating the city and its residents.

Friday December 5th, 1952, was an unusually still day when a high-pressure air mass stalled over the Thames Valley. When cold air suddenly arrived from the west, the air over London was trapped and a veil of thick fog soon enshrouded the city, blotting out its famous landmarks.

Because it had turned cold, Londoners lit or stoked up their coal fires, the smoke trapped by the increasingly dense blanket of fog. Within hours it began to turn a sickly shade of yellowish brown as the fumes rising from the industrious city were soaked up by the fog acting like a giant sponge. It was made worse by fumes from the diesel buses which had recently replaced London’s electric tram system and now added their contribution to the deadly brew.

At first Londoners, well used to the city’s ‘pea-soupers’, tried to carry on regardless, but by the following day it was clear that breathing in the foul air was not only unpleasant, but dangerous. One of the first victims was a prize cow that simply keeled over and died at Smithfield Market, having suffocated on the cloying smog.

People, especially heavy smokers or those with pre-existing respiratory conditions, found it increasing difficult to breathe. Even healthy individuals could find themselves vomiting or coughing up phlegm if they breathed in too much of the toxic smog. Infants, whose lungs were not fully developed or who had been ‘sickly’ with childhood ailments were particularly at risk, as were the elderly. Hundreds simply died in their sleep over the following few days.

There were serious road and rail accidents too, including a collision between two trains near London Bridge. Eventually, all transportation in the city was halted, both to prevent accidents and minimise the pollution from vehicles adding to the smog. Unable to get to work, most people simply stayed at home, using towels and blanket to block up gaps around doors and windows in an attempt to keep the smog out of their homes. Yet even holed up indoors, most still kept their fires alight, the smoke from their chimneys thickening the poisonous cloud now choking their city.

Those who did venture out took their lives in their hands, both through breathing in the toxic air, which reeked like rotten eggs, and because they simply could not see where they were going. In places visibility was down to inches, people feeling their way along walls and pavements, some becoming hopelessly lost in street they had known all their lives. Pavements became coated with a greasy black ooze and by the time people made it home through the smog they resembled coal miners, their faces, hair and nostrils blackened.

After several days the smog centred on London was 30 miles wide and getting denser with every passing hour. Those trapped inside it couldn’t even escape, as the city had ground to a halt, its transport systems paralysed by the smog and roads blocked by abandoned vehicles.

Relief finally came after five days, on December 9th, when a change in the weather saw winds picking up to steadily blow the smog out to the North Sea. By then, London’s undertakers had run out of coffins. Conservative estimates put the number of dead at 4,000 – a figure reached by comparing the number of deaths during the smog with that during the same period the previous year. But the mortality rate in London and surrounding areas was abnormally high for several months afterwards, some estimates later putting the number of smog-related deaths as high as 12,000.

There was growing pressure on the government to act and, after analysing the main causes of smog, in 1956 it passed the Clean Air Act. It restricted the burning of coal in urban areas, enabled local councils to set up smoke-free zones and offered grants to homeowners to convert from coal to alternative heating sources.

It would be many more years before the gradual switch to gas and electric heating made a significant impact on pollution in London, and smog continued to be an occasional problem, but never again on the scale witnessed in 1952.

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