Smudge pot
Encyclopedia
A smudge pot is an oil
Oil
An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....

-burning device used to prevent frost
Frost
Frost is the solid deposition of water vapor from saturated air. It is formed when solid surfaces are cooled to below the dew point of the adjacent air as well as below the freezing point of water. Frost crystals' size differ depending on time and water vapour available. Frost is also usually...

 on fruit trees
Orchard
An orchard is an intentional planting of trees or shrubs that is maintained for food production. Orchards comprise fruit or nut-producing trees which are grown for commercial production. Orchards are also sometimes a feature of large gardens, where they serve an aesthetic as well as a productive...

. Condensation
Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....

 of water vapor on particulate soot prevents condensation on plants and raises air temperature very slightly. Usually a smudge pot has a large round base with a chimney coming out of the middle of the base. The smudge pot is placed between trees in an orchard
Orchard
An orchard is an intentional planting of trees or shrubs that is maintained for food production. Orchards comprise fruit or nut-producing trees which are grown for commercial production. Orchards are also sometimes a feature of large gardens, where they serve an aesthetic as well as a productive...

, allowing the heat and smoke from the burning oil to prevent the accumulation of frost on the fruit of the grove. Smudge pots were developed after a disastrous freeze in Southern California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 in January 1913 wiped out a whole crop.

Smudge pots were commonly used for seven decades in areas such as California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

's numerous citrus groves.

Smudge pot use in Redlands, California
Redlands, California
Redlands is a city in San Bernardino County, California, United States. As of the 2010 census, the city had a population of 68,747, up from 63,591 at the 2000 census. The city is located east of downtown San Bernardino.- History :...

 groves continued into the 1970s, but fell out of favor as oil prices rose and environmental concerns increased. Pots came in two major styles: a single stack above a fuel oil-filled base, and a slightly taller version that featured a cambered neck and a re-breather feed pipe out of the side of the chimney that siphon
Siphon
The word siphon is sometimes used to refer to a wide variety of devices that involve the flow of liquids through tubes. But in the English language today, the word siphon usually refers to a tube in an inverted U shape which causes a liquid to flow uphill, above the surface of the reservoir,...

ed stack gas back into the burn chamber and which produced more complete combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

. Filler caps have a three- or four-hole flue control. The stem into the pot usually has a piece of oil-soaked wood secured inside the neck to aid in lighting the pot. Pots are ignited when the air temperature reaches 29 degrees Fahrenheit, and for each additional degree of drop, another hole is opened on the control cap. Below 25 degrees, there is nothing more that can be done to enhance the heating effects.

Some groves used natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 pots on lines from a gas source, but these are not "smudge pots" in the usual sense, and they represented only a fraction of the smudging practice. Sometimes, large smudge pots are used for heating large open buildings, such as mechanics workshops. In Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 they are called "choofers" because of the noise they make when lit — "choofa choofa choofa".

Lighting an Australian "choofer" is a tricky business. Because of the voluminous clouds of oily black smoke they produce when cold, they must be lit outside. This is accomplished by holding a burning rag next to the open damper on the fuel tank. The draught caused by the breeze passing through the chimney will draw the flames through the open damper into the fuel tank, where the surface of the fuel inside will light and burn instantly. Once the choofer is sufficiently warm, the damper may be closed until a steady rate of burning is attained, when the characteristic "choofa choofa choofa" noise is produced. If the damper is not closed, the choofa may choke itself with its own smoke, causing periodic "explosions" of unburnt gases in the chimney. Such explosions are not dangerous, but they are noisy and they produce a lot of smoke. Once the heater is burning hot enough, the smoke will disappear and the pot may be dragged slowly and carefully inside. They still produce dangerous gas, and must only be used in well-ventilated spaces.

Choofers will burn almost any flammable liquid fuel, including kerosene
Kerosene
Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...

, diesel fuel, or used sump oil.

Two other forms of oil heaters should be noted. Prior to the development of battery-powered safety blinkers on saw-horses, many highway departments used small oil-burning safety pot markers to denote work zones, and many railroad systems still rely on oil-fired switch heaters, long tubs of fuel with a wick, that fits between the ties and keeps snow and ice from fouling the points of a switch. This is generally only used in yard applications. Mainline switches are usually heated by natural gas heaters.

Other, more useful places that the smudge pot was used in was at construction sites and other cold places to take the chill out of buildings so workers can be comfortable, and for several decades (1920's-1970's) as emergency night landing illumination at remote airfields without electric runway lights, basically acting as a series of small bonfires.

Use in War

Smudge pots were used by the North Vietnamese during the Vietnam War
Vietnam War
The Vietnam War was a Cold War-era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. This war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of...

 in order to protect valuable targets. The oily black clouds of smoke produced from these smudge pots allegedly limited the ability of laser guided bombs to detect a target. The black clouds would diffuse the laser beam and break the laser's connection with its desired target.

Other significance

The smudge pot often became a symbolic prize in local football rivalries.

Today rivals:
  • Bonita High School
    Bonita High School
    Bonita High School is a high school located in the city of La Verne, California in the foothills of the San Gabriel Mountains. Opened in 1903, it was the first high school in the Bonita Unified School District. It moved to its current campus in 1959. The majority of its students come from Ramona...

     and San Dimas High School, in Southern California
    Southern California
    Southern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...

    , compete for a silver-plated smudge pot, and in
  • Redlands, California
    Redlands, California
    Redlands is a city in San Bernardino County, California, United States. As of the 2010 census, the city had a population of 68,747, up from 63,591 at the 2000 census. The city is located east of downtown San Bernardino.- History :...

    , Redlands High School
    Redlands High School
    Redlands High School is located in Redlands, California, United States. Founded in 1891, it is the oldest public high school in the State of California still functioning on its original site and the first "unified high school" formed from three elementary school districts...

     and Redlands East Valley High School
    Redlands East Valley High School
    Redlands East Valley High School is a public high school in Redlands, California, near the San Bernardino Mountains. The school opened in the 1997-1998 school year as part of the Redlands Unified School District.-Colors and mascot:The official school colors of REV are red, white and black...

    compete for a blue-and-red pot.
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