Smoke School History

The first visible emission law originated in New Orleans in 1859. A blacksmith's forge in the heart of the city started fires every morning that resulted in a significant amount of smoke and odor — a substantial public nuisance. When mixed with a heavy fog, common in New Orleans, the result was soot rain in the surrounding area.

A court case (City of New Orleans v. Lambert) resulted in an ordinance declaring the operation a public nuisance and prohibited an excessive amount of black smoke between 7:00 AM and 9:00 AM. However, the ordinance did not designate how much smoke was "excessive" — no criteria were defined. Similar laws were passed in Cincinnati and Chicago in the 1880s. These laws were the beginning of the regulation of visible emissions in the United States.

In the 1870s, Maximilien Ringelmann, a professor of agricultural engineering at the University of Paris, was working on tuning coal-fired boilers to optimize combustion. He created the Ringelmann Scale by developing a series of cards with black grids on white backgrounds such that the ink covered a specific percentage of each card. Each card was assigned a Ringelmann number. The Ringelmann Scale defines opacity in four levels that correlate to Ringelmann grid cards:

• Ringelmann 1 card: 20%
• Ringelmann 2 card: 40%
• Ringelmann 3 card: 60%
• Ringelmann 4 card: 80%
• Ringelmann 5: 100%

Before the Ringelmann Scale was used, there was no method to measure the opacity of smoke plumes — i.e., the level of nuisance to the public. It was difficult to enforce laws that used "excessive" as a standard. When the Ringelmann Scale was introduced in the U.S. in 1897, the demand, need, and political will facilitated rapid adoption. By 1912, more than 80% of cities with a population greater than 200,000 had a specific Ringelmann number standard to control local emission levels.

During this time, the federal government published a booklet "How To Tune Your Coal-Fired Burner" which included a Ringelmann chart. The booklet encouraged industrial organizations using coal to evaluate operations and helped them comply with local ordinances. Use of the Ringelmann Scale resulted in reducing coal use, improving economic results, and producing positive environmental outcomes.

The Ringelmann system's limitation is that it applies only to black smoke — it is a percent-based blackness scale. Attempts were made to create colored charts for other emission colors, but exact shades of emissions could seldom be matched.