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"...you will observe with Concern how long a useful Truth may be known, and exist, before it is generally receiv'd and practis'd on."

Benjamin Franklin, in a letter about lead poisoning, 31 July 1786

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Benjamin Franklin to Benjamin Vaughan, 31 July 1786, letterpress copy, Library of Congress.

⛽ 1. 1925: merely because of our fears

You met Thomas Midgley in the first lesson of this unit: in 1930 he breathed in a lungful of his new gas and blew out a candle to show it was safe. It was not the first time he had done something like that.

In the early 1920s, working for General Motors, Midgley had found that a few drops of a lead compound, tetraethyl lead, stopped car engines from "knocking", a juddering that wastes fuel and damages engines. It went on sale as a petrol additive under the name Ethyl. That lead is poisonous was not news. Look at the date on Franklin's letter at the top of this page.

In October 1924, workers making tetraethyl lead at a Standard Oil plant in New Jersey began to hallucinate and collapse. Five died, and dozens more were taken to hospital. On 30 October, at a press conference, Midgley poured the chemical over his hands and breathed in its vapour for about a minute, saying he could do it every day without harm. He had himself been treated for lead poisoning not long before.

Sales were paused, and in May 1925 the Surgeon General, the head of the US Public Health Service, called a conference in Washington. Public health scientists warned that lead from car exhausts would end up in the air that people breathed. Nobody could yet show that it was harming the public. Frank Howard of Standard Oil told the conference it would be "an unheard-of blunder if we should abandon a thing of this kind merely because of our fears."

A committee of experts reported in 1926 that there were "no good grounds for prohibiting" leaded petrol, as long as its sale was properly regulated, and it called for further studies. The studies were never funded. Leaded petrol was sold for cars somewhere in the world until July 2021, when Algeria became the last country to stop.

Proceedings of a Conference to Determine Whether or Not There Is a Public Health Question in the Manufacture, Distribution or Use of Tetraethyl Lead Gasoline, Public Health Bulletin No. 158 (Washington, DC: US Public Health Service, 1925).

The Use of Tetraethyl Lead Gasoline in Its Relation to Public Health, Public Health Bulletin No. 163 (Washington, DC: US Public Health Service, 1926).

William Kovarik, "Ethyl-Leaded Gasoline: How a Classic Occupational Disease Became an International Public Health Disaster," International Journal of Occupational and Environmental Health 11, no. 4 (2005): 384–97.

UN Environment Programme, "Era of Leaded Petrol Over, Eliminating a Major Threat to Human and Planetary Health," press release, 30 August 2021, https://www.unep.org/news-and-stories/press-release/era-leaded-petrol-over-eliminating-major-threat-human-and-planetary.

✍️ Write here, on your own:

  1. In 1925 nobody could prove that leaded petrol was harming the public, and nobody could prove that it was not. Who should have had to prove their case: the companies, that it was safe, or the critics, that it was harmful? Why?

  2. List everything that was riding on the decision, for everyone involved. Then mark each item: could a scientist measure it, or not?

📜 2. Montreal, 1987: before the proof

Sixty-two years later, a different room faced the same kind of question, this time about Midgley's other invention. This is what the people negotiating in Montreal knew in September 1987.

What they knew
The prediction Since 1974, chemists had argued that chlorine from CFCs would destroy ozone high in the stratosphere. You met that claim in the first lesson.
The models Computer models predicted a slow, gradual thinning of the ozone layer, spread across the world over many decades. They did not predict a hole over one continent.
The hole Since 1985, everyone knew that spring ozone over Antarctica had fallen by around 40 per cent in a decade. You traced how that was found in the last two lessons.
The cause Nobody had proved what was causing it. Three explanations were on the table: chlorine from CFCs, helped by clouds that form in the extreme Antarctic cold; air with less ozone in it rising from lower in the atmosphere; and changes in the sun over its eleven-year cycle.
The expedition Since August, a NASA-led team had been flying research aircraft into the ozone hole from Punta Arenas, in southern Chile, to test the explanations. Its results were not yet in.
The chemicals CFCs were in refrigerators, air conditioners, aerosol cans and foam packaging all over the world, and most of them were made and used in the richer countries.