On May 4, 1955 the Association of American Railroads held their 66th Annual Meeting of the General Claims Division. The featured speaker was a young general claims attorney for the Chesapeake and Ohio Railways. His name was Robert Straub, and the subject of his speech was “The Potential Dangers from Exposure to Diesel Locomotive Exhaust.” In the speech, Mr. Straub identified the known components of diesel exhaust, including carbon dioxide, water vapor, sulfur oxides, carbon monoxide, aldehydes, hydrogen, methane, smoke, nitrogen, “excess oxygen,” oxides of nitrogen, “allergens” and “cancerogens.”¹ In this excerpt, Mr. Straub discusses the “cancerogens” present in diesel exhaust:

“Recently, there has arisen the assertion of another serious medical consequence of inhaling diesel exhaust. The National Cancer Institute, in conjunction with the Railroad Retirement Board and several of the railroad brotherhoods, has initiated a survey to explore the possibility of linking lung cancer to the inhalation of diesel exhaust. This report is awaited. At the present, medical opinion is somewhat as follows: Among the constituents of diesel exhaust are aromatic hydrocarbons. Some aromatic hydrocarbon compounds may cause cancer. Others do not. In laboratory tests, cancerous growths have been produced on mice by subjecting them to the combination of aromatic hydrocarbons from diesel exhaust–not by inhalation, but by direct application to the skin. Whether the combination of these compounds existing in diesel exhaust will produce cancerous growths in the human lung remains to be seen, but we cannot overlook the potential danger.

“Assuming that such exposure can produce lung cancer the necessary degree of exposure in terms of duration and concentration will be important elements in arriving at even a provisional conclusion as to whether a cancer may have had its origin from exposure to diesel exhaust. If the considered opinion does not permit this conclusion, then such information will be of value in preparing appropriate defense against this type of a claim. Furthermore, it is to be remembered that diesel engines are not the sole disseminators of aromatic hydrocarbons. Exhaust from gasoline engines, incinerator soots, and other sources are known to introduce these compounds into the atmosphere.”²

On Dec 12, 1959–four years and seven months after Mr. Straub’s speech at the Association of American Railroads, the Journal of the American Medical Association (JAMA) published a paper by Isadore Kaplan. The article was titled “Relationship of Noxious Gases to Carcinoma of the Lung in Railroad Workers.”³ The impetus for the article was a lawsuit by a railroad machinist who claimed his lung cancer was the result of inhaling “diesel shop fumes.” Kaplan concluded there was “no relation between noxious fumes associated with railroad work and primary lung carcinoma.” But he arrived at his conclusion by comparing the expected and actual deaths from lung cancer during that time period, 1953-1958.

Interestingly, Kaplan included in his article a list of diesel exhaust components known or suspected at that time. The list included the following:
• pyrene
• fluoranthene
• chrysene
• fluorine
• 1,2 benzpyrene
• 3,4 benzpyrene
• 1,12 benzperylene

The Carbon Monoxide FELA case of 1961
In September, 1961 a FELA case reached the Court of Civil Appeals of Texas in Waco. The style of the case was Missouri Pacific Railroad Company v. Sims.⁴ The Plaintiff alleged that between September, 1954 and January, 1957 while working at Houston’s Settegast Yard, the employee had suffered chronic carbon monoxide poisoning from diesel fumes.
The Appeals Court concluded: “We think the record reflects that the plaintiff was subjected to an unnecessary hazard which could have easily been eliminated, and amply supports the findings of the jury. Moreover, we think that the record as a whole sustains such findings, and that they are not against the great weight and preponderance of the evidence under the rule of law in re King’s Estate, 150 Tex. 662, 224 SW 2nd 660.”
Trapping benzo(a)pyrene
Each chemical substance has its own singular set of physical properties: melting point, temperature of vaporization, specific gravity, solubility and so forth. This set of values can vary between similar substances by only a few degrees of temperature. Thus, it can be difficult to separate individual compounds from the soup of chemicals that can emerge from an exhaust stack. In 1775 the British surgeon Percivall Pott linked scrotal cancer in chimney sweeps to their exposure to soot. By 1933, a component of soot, 3,4-benzo(a)pyrene, was identified as a likely carcinogen. However, isolating 3,4-benzo(a)pyrene proved to be difficult. 3,4-benzo(a)pyrene is a solid below 352°F, and vaporizes at 887°F. While a diesel engine can run at a relatively cool 160°F, the exhaust gases–including 2,4-benzo(a)pyrene– can reach temperatures between 500-1000°F–but then quickly cools to ambient temperature not long after it leaves the exhaust stack. The researchers may suspect the presence of 3,4-benzo(a)pyrene in exhaust gas, but it was difficult or impossible to accurately determine how much of the chemical was actually in the exhaust stream.

Here is why: depending entirely on the temperature of the exhaust (which varies depending on the distance from the stack), the 3,4-benzo(a)pyrene might be a solid, a liquid or a gas. If the sampling method involved capturing (high-temperature) vapors or liquids, the researchers would miss the solids. If a filter was used to collect solids, the vapors would pass through unimpeded. In fact, the problem was even more difficult than that:

In 1958 a team of British researchers found that benzo(a)pyrene would remain on a sampling filter only if the collection temperature did not exceed the astonishingly low temperature of 65°F.⁵ This meant, if the diesel exhaust sample was taken in a warm climate in the summertime (say, in Texas), there would likely be no benzo(a)pyrene left to analyze. As a result, the researchers could assume, wrongly, that diesel exhaust contained no BAP at all.

It took three researchers from the Robert A. Taft Sanitary Engineering Center, Public Health Service, Cincinnati OH to solve the problem. The scientists, Robert L. Stenburg, Darryl J. von Lehmden and Robert P. Hangebrauck ran the exhaust gas through a series of common industrial hygiene devices called water bubblers and condensate traps immersed in an ice-water bath. Doing that ensured the BAP would be in the form of a solid as the exhaust gas as it moved through the ice-cooled bubblers and traps. At the end of the apparatus, the researchers installed a high-efficiency filter to collect the solid crystals of 3,4-benzo(a)pyrene.

And it worked.⁶

The procedure was published in the American Industrial Hygiene Association Journal in August, 1961. Now, researchers finally had an effective means of characterizing diesel exhaust for carcinogens such as BAP. And of course, so did the railroads.

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