What happened in the 1952 London "killer fog"?

SDStaff John Corrado replies:

Katie, it’s obvious you aren’t an aficionado of horror novels; otherwise, you’d be quite familiar with the idea of a “killer” fog. A century ago writers used fog to mask the landscape and hide the horrors within — see Lovecraft, Stoker, and Doyle’s works. By the 1970’s, though, the emphasis had shifted to the fog itself being malevolent. For example, John Carpenter’s The Fog, released in 1980, or Stephen King’s short story The Mist.

Why the change? Stephen King writes in Danse Macabre that any good horror story must touch upon a source of realistic horror for the reader by probing his or her own fears. Such as, “What horrible things are being let into the air through pollution?” King brings up the example of chemical gases being released accidentally by the Army — several sheep were killed by the toxins, but had the wind been blowing the other way, Salt Lake City would have gotten a dose of something a little more dangerous to a Mormon than coffee.

With that in mind, let’s take a look at the Killer Fog of London.

Actually, describing it as “fog” is wrong; Londoners had long since coined the term “smog” to describe the dense combination of smoke and fog that occasionally covered the city. Most of that smoke was pollution, caused by local factories and open coal fires used to heat houses. Add to that the fact that London had just scrapped all of its electric tramcars and replaced them with diesel buses, and you had a massive amount of pollution that, attached to the fog, settled down on London. Trapped by the surrounding hills and a stagnant mass of warm air above it, it would remain in London for over a week.

Pollution can bring about sickness and death in a myriad of ways. For example, high ozone levels can cause cardiac arrhythmia. But the main problem with the fog was a more basic one. By adding particles to the air and reducing oxygen, the fog made it harder for people just to breathe. Doctors in London reported people coming into the hospitals gasping for breath.

It’s hard to say how many people died due to the fog of ’52 — estimates range from two to four thousand people. Because doctors didn’t write “killer smog” under “cause of death,” we can’t directly attribute deaths to the smog. But we do know this. The average death rate in London prior to the fog was 135 people per day. On the second day of the fog, that number jumped to over 500 people, and didn’t drop below 200 per day for over three weeks. And lest you think that the people who passed away were just the feeble and dying who would have kicked the bucket soon anyway, there was no major drop in the death rate afterward. Which means that the people who died probably could have lived months or years longer were it not for the fog.

The London government of the time tried to ignore any evidence that pollution was responsible for the catastrophe, but public outcry and scientific evidence would later push Parliament to pass the Clean Air Act of 1956.

SDStaff John Corrado, Straight Dope Science Advisory Board

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