Clear skies dawned over London on December 5, 1952. A wintry cold snap had gripped the British capital for weeks, and as Londoners awoke, coal fireplaces were stoked in homes and businesses across the city to take the chill from the early morning air.

As the day progressed, a veil of fog—not unusual in a city famous for its cool, misty weather—began to enshroud Big Ben, St. Paul’s Cathedral, London Bridge and other city landmarks.

Within a few hours, however, the fog began to turn a sickly shade of yellowish brown as it mixed with thousands of tons of soot pumped into the air by London’s factory smokestacks, chimneys and automobiles. Smoky, diesel-fueled buses had recently replaced the city’s electric tram system, adding to the toxic brew.

Nonetheless, Londoners went about their business with typical British reserve, ignoring the foul air as much as possible. But within a day, it became impossible to ignore the unfolding crisis.

Fog, combined with smoke to produce smog, was nothing new in London, but this particular “pea souper” quickly thickened into a poisonous stew unlike anything the city had ever experienced.

A high-pressure weather system had stalled over southern England and caused a temperature inversion, in which a layer of warm air high above the surface trapped the stagnant, cold air at ground level.

The temperature inversion prevented London’s sulfurous coal smoke from rising, and with nary a breeze to be found, there was no wind to disperse the soot-laden smog. The noxious, 30-mile-wide air mass, teeming with acrid sulfur particles, reeked like rotten eggs—and it was getting worse every day.

The smog was so dense that residents in some sections of the city were unable to see their feet as they walked. For five days, the Great Smog paralyzed London and crippled all transportation, except for the London Underground train system.

Because of poor visibility, boat traffic on the River Thames came to a halt. Flights were grounded and trains cancelled. Even during the middle of the day, drivers turned on their headlights and hanged their heads out car windows to inch ahead through the thick gloom. Many found the effort futile and simply abandoned their cars.

Conductors holding flashlights walked in front of London’s iconic double-decker buses to guide drivers down city streets. Wheezing pedestrians groped their way around the city’s neighborhoods and tried not to slip on the greasy black ooze that coated sidewalks. By the time they returned home, their faces and nostrils blackened by the air, Londoners resembled coal miners.

Authorities advised parents to keep their children home from school, partly from fear they would get lost in the blinding smog. Looting, burglaries and purse snatchings increased as emboldened criminals easily vanished into the darkness.

Weekend soccer games were cancelled, although Oxford and Cambridge carried on with their annual cross-country competition at Wimbledon Common with the help of track marshals who continually shouted, “This way, this way, Oxford and Cambridge” as runners materialized out of the thick haze.

The smog seeped inside buildings as well. A greasy grime covered exposed surfaces, and movie theaters closed as the yellow haze made it impossible for ticket-holders to see the screen.

The Great Smog of 1952 was much more than a nuisance. It was lethal, particularly for the elderly, young children and those with respiratory problems. Heavy smokers were especially vulnerable because of their already-impaired lungs, and smoking was common at the time, especially among men.

It wasn’t until undertakers began to run out of coffins and florists out of bouquets that the deadly impact of the Great Smog was realized. Deaths from bronchitis and pneumonia increased more than sevenfold. The death rate in London’s East End increased ninefold.

Initial reports estimated that about 4,000 died prematurely in the immediate aftermath of the smog.

The detrimental effects lingered, however, and death rates remained well above normal into the summer of 1953. Many experts now estimate the Great Smog claimed at least 8,000 lives, and perhaps as many as 12,000.

The effects of the Big Smoke weren’t limited to people: Birds lost in the fog crashed into buildings. Eleven prize heifers brought to Earls Court for the famed Smithfield Show choked to death, and breeders fashioned improvised gas masks for their cattle by soaking grain sacks in whiskey.

After five days of living in a sulfurous hell, the Great Smog finally lifted on December 9, when a brisk wind from the west swept the toxic cloud away from London and out to the North Sea.

Initially, the British government was slow to act during the Great Smog. Heavy fog was, after all, a common occurrence in London and there was, according to most reports, no immediate sense of urgency to this smog event.

Following a government investigation, however, Parliament passed the Clean Air Act of 1956, which restricted the burning of coal in urban areas and authorized local councils to set up smoke-free zones. Homeowners received grants to convert from coal to alternative heating systems.

The transition away from coal as the city’s primary heating source toward gas, oil and electricity took years, and during that time deadly fogs periodically occurred, such as one that killed about 750 people in 1962. None of them, however, approached the scale of the 1952 Great Smog.