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Flash point defines the lowest temperature of a flammable liquid, adjusted to account for variations in atmospheric pressure from 101.3 kPa, at which application of an ignition source causes the vapours of the liquid to ignite under specified conditions of the test. At the flash point, the liquid provides sufficient vapour near the surface of the liquid that is capable of forming ignitable mixture with air. On the other hand, fire point is the lowest temperature at which the liquid continues to burn for at least 5 seconds even after withdrawing the ignition source.


At Prime Process Safety Center, the flash point and fire point of petroleum and other flammable liquids are performed via the Pensky Martens Closed Cup method as well as the Cleveland Open Cup method.

In the closed cup method, the liquid to be tested is poured into the test cup up to the mark and placed into the cup holder. The lid together with the thermometer and stirrer is placed on the cup holder. The heater is turned on and adjusted to about 50% to ensure a heating rate of about 1ᣞC per minute. Stirring of the liquid is adjusted to about 250 r/min. An ignition source or flame of about 3.2 mm to 4.8 mm in diameter is lighted and dipped into the vapor space of the liquid for about 0.5s and a visual observation is made of any flash. If no flash is observed at the beginning, the test is continued until an observation is made after every 2ᣞC of temperature rise. If flash is observed at the first trial, the sample is cooled down to about 18ᣞC below the observed flash point and the test repeated. The open cup method is similar to the closed cup method with the only difference being that the test is performed with no lid on top of the test cup, thus flash point measured for the open cup is usually higher than the closed cup. The Cleveland Open Cup tester is used in determinning the Fire point of flammable liquid. In the fire point test, it is ensured that the liquid continues to burn for at least five seconds after withdrawing the ignition source.

Applicable Standard

ASTM D 93, ‘’Flash Point by Pensky-Martens Closed Cup Tester’’ / ISO 2719, Determination of Flash Point by Pensky-Martens Closed Cup method’’ / ASTM D 3828, ‘’Standard Test Method for Flash Point by Small Scale Closed Cup Tester’’/ ASTM D 92, ‘’Standard Test Method for Flash and Fire Points by Cleveland Open Cup Tester’’

Data Interpretation

Below are some examples of flash points of common flammable liquids.

Hydrocarbon Purity, mol% Flash Point (C) Tolerance
n-Decane 99+ 52.8 2.6
n-Undecane 99+ 68.7 3.4
n-tetradecane 99+ 109.3 5.4
n-hexadecane 99+ 133.9 6.7

Understanding the flash point is crucial because it provides insight into the product’s volatility and flammability, making it a key factor in assessing potential fire hazards and risks during storage, transportation, and usage. A substance with a low flash-point is considered highly flammable and a product with a high flashpoint is considered less flammable. Flash point will also indicate the possible presence of highly volatile and flammable materials in a relatively non-volatile or non-flammable substance.

Why work with Prime Process Safety Center

  • Prime Process Safety Center is a leader in process safety testing with very experienced laboratory personnel. At Prime Process Safety Center our goal is to provide accurate, reliable and defensible data that meets industry and regulatory standards. We understand the need for the quality of your data, and we work assiduously to achieve just that.
  • We are knowledgeable and experienced in performing flash and fire point tests, ensuring accurate and reliable results.
  • We have state-of-the-art flash and fire point testing equipment, providing precise and sensitive measurements.
  • We follow strict testing protocols and quality control measures to ensure consistent and reliable test results.
  • Our team can interpret and analyze the data obtained from the tests, providing valuable insights and recommendations for your specific application or research.


What is the Difference Between Flash Point and Fire Point?

Answer: Flash point is the lowest temperature at which a substance emits enough vapor to ignite momentarily with a flame when exposed to an ignition source. Fire point is the temperature at which sustained combustion of the substance occurs.

Why Are Flash Point and Fire Point Important?

Answer: Flash point and fire point provide critical information about a substance’s flammability and ignition characteristics, helping determine safe handling, storage, and transportation conditions to prevent fires or accidents.

How Are Flash Point and Fire Point Determined?

Answer: Flash point is typically determined using standardized methods like the Pensky-Martens closed cup or Cleveland open cup apparatus, heating the substance and applying an ignition source. Fire point is measured when sustained combustion occurs after the flash point.

What Factors Influence Flash Point and Fire Point?

Answer: Several factors affect these points, including the chemical composition of the substance, volatility, presence of impurities, atmospheric pressure, and the method used for testing.

What Are the Practical Applications of Flash Point and Fire Point?

Answer: Flash point and fire point data are essential for classifying substances, designing safe storage and handling protocols, selecting appropriate fire suppression systems, and ensuring workplace safety in industries handling flammable materials.