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Guilherme Mazui

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What is the Difference Between Open Cup and Closed Cup Flash Point?

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The main difference between open cup and closed cup flash points lies in the method used to measure the temperature at which a volatile substance ignites. Here are the key differences between the two methods:

  • Open Cup Flash Point: This method is conducted in a vessel that is exposed to the outside air. The temperature of the substance is gradually raised, and an ignition source is passed over the top until it reaches a point at which it "flashes" and ignites. Open cup tests simulate the potential ignition of a liquid spillage in uncontained conditions, such as a pool of liquid spilled on the floor. The most commonly used open cup method is the Cleveland Open Cup (COC).
  • Closed Cup Flash Point: This method is conducted inside a closed vessel, which is not open to the air. The lid is sealed, and the ignition source is introduced into the vessel itself, allowing for a closer approximation to real-life conditions (such as those found inside a fuel tank). Closed cup tests aim to simulate a liquid in a closed or semi-closed contained environment. There are four main kinds of closed cup flash points: Pensky-Martens, Abel, Tag, and the most widely-used, Small Scale, which is often known as Setaflash.

Closed cup flash point testers typically give lower values for the flash point than open cup testers, with a difference of around 5-10 °C (9-18 °F). Closed cup tests are usually specified due to improved precision.

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  • What is the Difference Between Open Cup and Closed Cup Flash Point?
  • Comparative Table: Open Cup vs Closed Cup Flash Point

    • Comparative Table: Open Cup vs Closed Cup Flash Point

    The difference between open cup and closed cup flash point lies in the method used to measure the lowest temperature at which a volatile substance can ignite. Here is a comparison table of the two methods:

    Method Description Flash Point
    Open Cup Measured in a vessel exposed to the air outside, with the vapor above the liquid in equilibrium with the liquid. Commonly used methods include the Cleveland Open Cup (COC). Usually higher than closed cup flash points.
    Closed Cup Measured in a closed vessel, with the vapor above the liquid not in equilibrium with the liquid. There are two forms: non-equilibrial and equilibrial methods. Common methods include Pensky Martens, Abel, Tag, and the widely-used Small Scale or Setaflash. Usually lower than open cup flash points.

    Open cup flash points are often used to mimic conditions in open spaces, while closed cup flash points simulate conditions in confined or restricted spaces. Due to their better precision and ability to detect contaminants, closed cup methods are commonly specified in regulations and product specifications.

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    Guilherme Mazui

    Guilherme Mazui is graduated in journalism from the Federal University of Minas Gerais (UFMG) and a master's degree in Communication from the University of São Paulo (USP). In addition, he has experience in advertising writing and has worked as a content editor in several companies.