The Killer Fog of '52 Fifty years ago, a toxic mix of dense fog and sooty black coal smoke descended on London, essentially suffocating thousands to death.

The Killer Fog of '52

Thousands Died as Poisonous Air Smothered London

The 1952 smog killed Rosemary Merritt's father. Hear her story.

Audio will be available later today.

Central London during the killer smog, December 1952. 'When Smoke Ran Like Water,' Perseus Books hide caption

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'When Smoke Ran Like Water,' Perseus Books

London's Piccadilly Circus at midday. 'When Smoke Ran Like Water,' Perseus Books hide caption

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'When Smoke Ran Like Water,' Perseus Books

Maureen Scholes, a nurse at the Royal London Hospital in 1952, says the smog penetrated through clothes, blackening undergarments. Royal London Hospital Archives and Museum hide caption

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Royal London Hospital Archives and Museum

London's death rate shot up during the week of Dec. 5, 1952, with the smog killing thousands already weakened by respiratory illnesses. Paul Lioy, Rutgers University hide caption

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Paul Lioy, Rutgers University

Fifty years ago this month, a toxic mix of dense fog and sooty black coal smoke killed thousands of Londoners in four days. It remains the deadliest environmental episode in recorded history.

The so-called killer fog is not an especially well-remembered event, even though it changed the way the world looks at pollution. Before the incident, people in cities tended to accept pollution as a part of life. Afterward, more and more, they fought to limit the poisonous side effects of the industrial age.

NPR's John Nielsen went to London to prepare two reports on the killer fog of 1952.

Funeral director Stan Cribb of T. Cribb and Sons has led thousands of funeral trains through the smoggy streets of London. But he says the 1952 event dwarfs all others he has seen. He remembers the moment he saw the first gray wisps:

"You had this swirling," Cribb recalls, "like somebody had set a load of car tires on fire."

Cribb was then a mortician's assistant, working for Tom Cribb, his elderly uncle. On Friday Dec. 5, they were driving to a wake, with a line of cars full of mourners close behind. Neither man knew a catastrophe was brewing. They didn't know that a mass of stagnant air had just clamped a lid over London, trapping the smoke from millions of residential coal fires at ground level.

Cribb remembers being stunned by the blackness of the gathering fog. After a few minutes he couldn't see the curb from his spot behind the wheel. After a few more minutes, Tom Cribb got out and started walking in front of the hearse, to keep his nephew on the road. He carried a powerful hurricane lantern in one hand, but it was useless.

"It's like you were blind," says Cribb.

Everyone in London walked blind for the next four days. By the time the smog blew off on Tuesday Dec. 9, thousands of Londoners were dead, and thousands more were about to die. Those who had survived no longer spoke of London's romantic pea-soup fog.

As the smoke coming out of London's chimneys mixed with natural fog, the air turned colder. Londoners heaped more coal on their fires, making more smoke. Soon it was so dark some said they couldn't see their feet.

By Sunday, Dec. 7, visibility fell to one foot.

Roads were littered with abandoned cars. Midday concerts were cancelled due to total darkness. Archivists at the British Museum found smog lurking in the book stacks. Cattle in the city's Smithfield market were killed and thrown away before they could be slaughtered and sold — their lungs were black.

On the second day of the smog, Saturday, Dec. 6, 500 people died in London. When the ambulances stopped running, thousands of gasping Londoners walked through the smog to the city's hospitals.

The lips of the dying were blue. Heavy smoking and chronic exposure to pollution had already weakened the lungs of those who fell ill during the smog. Particulates and acids in the killer brew finished the job by triggering massive inflammations. In essence, the dead had suffocated.

Some 900 more people died on Tuesday, Dec. 9, 1952. Then the wind swept in unexpectedly. The killer fog vanished as quickly as it had arrived.

In his 60 years as a mortician, Stan Cribb has only stopped two funeral trains. Once in the fog of '52, and once when Nazi warplanes bombed the road around him. In the blitz, 30,000 Londoners died. According a recent study in the journal Environmental Health Perspectives, 12,000 may have been killed by the great smog.