Smoke School Lecture Course




Section 2

History of Opacity Observations

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1859: City of New Orleans vs. Lambert

City of New Orleans vs. Lambert

New Orleans had a smoke control ordinance that was being violated by a blacksmith shop. The court ruled in favor of the city which was one of the first documented cases where an air pollution ordinance was upheld. The reasoning behind the ruling was that the smoke from the blacksmith’s shop was a “nuisance” to the population by violating their personal comfort. The ruling was not made due to health concerns.

1897: Max Ringelmann Develops Ringelmann Scale.

Max Ringelmann Develops Ringelmann Scale.

In an effort to measure the combustion efficiency of coal-fired boilers, French professor Max Ringelmann developed a system of grids to measure the density of smoke. The exact dimensions of the grids and the line thicknesses were determined by Ringelman so they would appear a shade of grey when viewed from a distance. The color from the grid was compared to the color of the smoke from the boiler. The grid that most accurately represented the density of the smoke was the Ringelmann number of the smoke. By adjusting the fuel/air ratio, Ringelman could increase the efficiency of the boiler and decrease the smoke.

Ringelmann No. 1 – Equivalent to 20% opacity.
Ringelmann No. 2 – Equivalent to 40% opacity.
Ringelmann No. 3 – Equivalent to 60% opacity.
Ringelmann No. 4 – Equivalent to 80% opacity.

1899: Ringlemann Scale used in U.S.

Ringlemann Scale used in U.S.

The American Society of Mechanical Engineers started using the Ringelmann scale as the official scale to determine smoke density when monitoring combustion efficiency. The scale was never intended to be used as a regulatory device, but after its introduction in the U.S., many municipalities adopted it to enforce smoke control ordinances.

1910: Statute Upholds Use of Ringelmann Scale

Statute Upholds Use of Ringelmann Scale

In Rochester, NY, a statute prohibited smoke from 5:00 A.M. to 7:30 A.M. and allowed dense smoke for only 5 minutes in every four-hour period. The statute was most likely intended to reduce “nuisance” complaints from morning commuters.

1912: Nationwide Acceptance of Smoke Ordinances

Nationwide Acceptance of Smoke Ordinances

By 1912, 23 of the 28 largest U.S. cities had adopted smoke control ordinances. Although ordinances were becoming more common, they mostly referred to excessive smoke as a nuisance rather than a health concern.

1916: Northwestern Laundry vs. Des Moines

Northwestern Laundry vs. Des Moines

This was a landmark case filed by Northwestern Laundry against the smoke abatement board of Des Moines, Iowa. The smoke abatement board enforced an ordinance that declared dense smoke in certain portions of the city was a nuisance. Northwestern Laundry claimed the ordinance was void because it required remodeling nearly all of their furnaces and the Ringelmann scale was arbitrary. The court dismissed the case and stated that the state or its municipalities could declare dense smoke a nuisance and uphold such ordinance even if it required the discontinued use of property or subjected the occupant with a large expense to comply with the ordinance. This case was cited as a precedent in many similar cases.

1945: Los Angeles Develops Equivalent Opacity

Los Angeles Develops Equivalent Opacity

Because the Ringelmann scale was designed to be used on sources of black smoke, sources of white smoke were largely unaffected by smoke ordinances. In an effort to control air pollution, the city of Los Angeles developed the equivalent opacity concept which extended the use of Ringelmann charts to sources of white smoke. Equivalent opacity simply meant the density of white smoke could be measured by comparing it to an equivalent shade of grey on the Ringelmann scale.

1948: Donora, Pennsylvania

Donora, Pennsylvania

An air pollution episode in Donora kills 20 people. Over 6000 residents became ill due to uncontrolled emissions from industrial facilities.

1950: California Passes California Rule 50A

California Passes California Rule 50A

Rule 50A limited the density of smoke based on comparisons to the Ringelmann scale. Rule 50A would later be adopted by nearly every state and eventually lead to the development of a Federal standard that limited opacity (EPA Method 9).

1953: First Smoke School

First Smoke School

Los Angeles County started the first “smoke school” for reading black smoke. Smoke inspectors could now attend a smoke school to determine smoke opacity instead of using the Ringelmann scale.

1955: Air Pollution Control Act

The federal government enacted the first Air Pollution Control Act to provide funding for research and technical assistance to better understand the causes and effects of air pollution.

1963: Clean Air Act

Clean Air Act

This was the first Federal Clean Air Act. It empowered the Secretary of Health, Education, and Welfare to define air quality criteria based on scientific studies and provided grants to state and local air pollution control districts.

1967: Federal Air Quality Act

The Federal Air Quality Act established a framework for defining air quality control regions based on meteorological and topographical factors of air pollution. It also required states to adopt ambient air quality standards.

1968: AP-30 Published

AP-30 Published

AP-30 described a study performed by the federal government regarding the accuracy of human observations of opacity. The study consisted of thousands of opacity readings of black and white smoke. The study found that 100% of the human observations had an error of less than 7.5% for black smoke readings and 99% had an error of less than 7.5% on white smoke readings. This study would be the basis for the testing requirements of EPA Method 9.

1970: Creation of EPA

Creation of EPA

The Environmental Protection Agency (EPA) was created by combining numerous federal agencies. It was created to consolidate environmental activities at the federal level and to support state and municipal environmental control and research efforts. During the same year, Federal New Source Performance Standards for opacity were published.

1974: EPA Method 9 Established

 EPA Method 9 Established

EPA Method 9 is a test method for determining the opacity of smoke through visual observations. EPA Method 9 requires an individual to become certified at a smoke school to perform opacity observations. With the establishment of this test method, the use of the Ringelmann scale was widely abandoned.

1982: EPA Method 22 Established

Unlike Method 9, Method 22 addresses the presence or absence of visible emissions, not the actual opacity.