Flash point

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Flaming cocktails with a flash point lower than room temperature. Flaming cocktails.jpg
Flaming cocktails with a flash point lower than room temperature.

The flash point of a material is the "lowest liquid temperature at which, under certain standardized conditions, a liquid gives off vapours in a quantity such as to be capable of forming an ignitable vapour/air mixture". (EN 60079-10-1)

Contents

The flash point is sometimes confused with the autoignition temperature, the temperature that causes spontaneous ignition. The fire point is the lowest temperature at which the vapors keep burning after the ignition source is removed. It is higher than the flash point, because at the flash point vapor may not be produced fast enough to sustain combustion. [1] Neither flash point nor fire point depends directly on the ignition source temperature, but ignition source temperature is far higher than either the flash or fire point.

Fuels

The flash point is a descriptive characteristic that is used to distinguish between flammable fuels, such as petrol (also known as gasoline), and combustible fuels, such as diesel.

It is also used to characterize the fire hazards of fuels. Fuels which have a flash point less than 37.8 °C (100.0 °F) are called flammable, whereas fuels having a flash point above that temperature are called combustible. [2]

Mechanism

All liquids have a specific vapor pressure, which is a function of that liquid's temperature and is subject to Boyle's Law. As temperature increases, vapor pressure increases. As vapor pressure increases, the concentration of vapor of a flammable or combustible liquid in the air increases. Hence, temperature determines the concentration of vapor of the flammable liquid in the air. A certain concentration of a flammable or combustible vapor is necessary to sustain combustion in air, the lower flammable limit, and that concentration is specific to each flammable or combustible liquid. The flash point is the lowest temperature at which there will be enough flammable vapor to induce ignition when an ignition source is applied.[ citation needed ]

Measurement

There are two basic types of flash point measurement: open cup and closed cup. [3] In open cup devices, the sample is contained in an open cup which is heated and, at intervals, a flame brought over the surface. The measured flash point will actually vary with the height of the flame above the liquid surface and, at sufficient height, the measured flash point temperature will coincide with the fire point. The best-known example is the Cleveland open cup (COC). [4]

There are two types of closed cup testers: non-equilibrial, such as Pensky-Martens, where the vapours above the liquid are not in temperature equilibrium with the liquid, and equilibrial, such as Small Scale (commonly known as Setaflash), where the vapours are deemed to be in temperature equilibrium with the liquid. In both these types, the cups are sealed with a lid through which the ignition source can be introduced. Closed cup testers normally give lower values for the flash point than open cup (typically 5–10 °C or 9–18 °F lower) and are a better approximation to the temperature at which the vapour pressure reaches the lower flammable limit. In addition to the Penskey-Martens flash point testers, other non-equilibrial testers include TAG and Abel, both of which are capable of cooling the sample below ambient for low flash point materials. The TAG flash point tester adheres to ASTM D56 and has no stirrer, while the Abel flash point testers adheres to IP 170 and ISO 13736 and has a stirring motor so the sample is stirred during testing.

The flash point is an empirical measurement rather than a fundamental physical parameter. The measured value will vary with equipment and test protocol variations, including temperature ramp rate (in automated testers), time allowed for the sample to equilibrate, sample volume and whether the sample is stirred.

Methods for determining the flash point of a liquid are specified in many standards. For example, testing by the Pensky-Martens closed cup method is detailed in ASTM D93, IP34, ISO 2719, DIN 51758, JIS K2265 and AFNOR M07-019. Determination of flash point by the Small Scale closed cup method is detailed in ASTM D3828 and D3278, EN ISO 3679 and 3680, and IP 523 and 524.

CEN/TR 15138 Guide to Flash Point Testing and ISO TR 29662 Guidance for Flash Point Testing cover the key aspects of flash point testing.

Examples

FuelFlash pointAutoignition
temperature
Ethanol (70%)16.6 °C (61.9 °F) [5] 363 °C (685 °F) [5]
Coleman fuel (White Gas)−4 °C (25 °F) [6] 215 °C (419 °F) [6]
Gasoline (petrol)−43 °C (−45 °F) [7] 280 °C (536 °F) [8]
Diesel (2-D) >52 °C (126 °F) [7] 210 °C (410 °F) [8]
Jet fuel (A/A-1) >38 °C (100 °F)210 °C (410 °F)
Kerosene >38–72 °C (100–162 °F)220 °C (428 °F)
Vegetable oil (canola)327 °C (621 °F)424 °C (795 °F) [9]
Biodiesel >130 °C (266 °F)

Gasoline (petrol) is a fuel used in a spark-ignition engine. The fuel is mixed with air within its flammable limits and heated by compression and subject to Boyle's Law above its flash point, then ignited by the spark plug. To ignite, the fuel must have a low flash point, but in order to avoid preignition caused by residual heat in a hot combustion chamber, the fuel must have a high autoignition temperature.

Diesel fuel flash points vary between 52 and 96 °C (126 and 205 °F). Diesel is suitable for use in a compression-ignition engine. Air is compressed until it heats above the autoignition temperature of the fuel, which is then injected as a high-pressure spray, keeping the fuel-air mix within flammable limits. A diesel-fueled engine has no ignition source (such as the spark plugs in a gasoline engine), so diesel fuel can have a high flash point, but must have a low autoignition temperature.

Jet fuel flash points also vary with the composition of the fuel. Both Jet A and Jet A-1 have flash points between 38 and 66 °C (100 and 151 °F), close to that of off-the-shelf kerosene. Yet both Jet B and JP-4 have flash points between −23 and −1 °C (−9 and 30 °F).

Standardization

Automatic Pensky-Martens closed cup tester with an integrated fire extinguisher APM-932hd-1.png
Automatic Pensky-Martens closed cup tester with an integrated fire extinguisher

Flash points of substances are measured according to standard test methods described and defined in a 1938 publication by T.L. Ainsley of South Shields entitled "Sea Transport of Petroleum" (Capt. P. Jansen). The test methodology defines the apparatus required to carry out the measurement, key test parameters, the procedure for the operator or automated apparatus to follow, and the precision of the test method. Standard test methods are written and controlled by a number of national and international committees and organizations. The three main bodies are the CEN / ISO Joint Working Group on Flash Point (JWG-FP), ASTM D02.8B Flammability Section and the Energy Institute's TMS SC-B-4 Flammability Panel.

See also

Related Research Articles

The autoignition temperature or kindling point of a substance is the lowest temperature in which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to supply the activation energy needed for combustion. The temperature at which a chemical ignites decreases as the pressure is increased.

A flashover is the near-simultaneous ignition of most of the directly exposed combustible material in an enclosed area. When certain organic materials are heated, they undergo thermal decomposition and release flammable gases. Flashover occurs when the majority of the exposed surfaces in a space are heated to their autoignition temperature and emit flammable gases. Flashover normally occurs at 500 °C (932 °F) or 590 °C (1,100 °F) for ordinary combustibles and an incident heat flux at floor level of 20 kilowatts per square metre (2.5 hp/sq ft).

The fire point of a fuel is the lowest temperature at which the vapour of that fuel will continue to burn for at least five seconds after ignition by an open flame of standard dimension. At the flash point, a lower temperature, a substance will ignite briefly, but vapor might not be produced at a rate to sustain the fire. Most tables of material properties will only list material flash points. In general the fire point can be assumed to be about 10 °C higher than the flash point, although this is no substitute for testing if the fire point is safety critical.

<span class="mw-page-title-main">Liquid fuel</span> Liquids that can be used to create energy

Liquid fuels are combustible or energy-generating molecules that can be harnessed to create mechanical energy, usually producing kinetic energy; they also must take the shape of their container. It is the fumes of liquid fuels that are flammable instead of the fluid. Most liquid fuels in widespread use are derived from fossil fuels; however, there are several types, such as hydrogen fuel, ethanol, and biodiesel, which are also categorized as a liquid fuel. Many liquid fuels play a primary role in transportation and the economy.

<span class="mw-page-title-main">Fire triangle</span> Model for understanding the ingredients for fires

The fire triangle or combustion triangle is a simple model for understanding the necessary ingredients for most fires.

Cetane number is an indicator of the combustion speed of diesel fuel and compression needed for ignition. It plays a similar role for diesel as octane rating does for gasoline. The CN is an important factor in determining the quality of diesel fuel, but not the only one; other measurements of diesel fuel's quality include energy content, density, lubricity, cold-flow properties and sulphur content.

<span class="mw-page-title-main">Fire making</span> Process of starting a fire artificially

Fire making, fire lighting or fire craft is the process of artificially starting a fire. It requires completing the fire triangle, usually by heating tinder above its autoignition temperature.

<span class="mw-page-title-main">Electrical equipment in hazardous areas</span> Electrical equipment in places where fire or explosion hazards may exist

In electrical and safety engineering, hazardous locations are places where fire or explosion hazards may exist. Sources of such hazards include gases, vapors, dust, fibers, and flyings, which are combustible or flammable. Electrical equipment installed in such locations could provide an ignition source, due to electrical arcing, or high temperature. Standards and regulations exist to identify such locations, classify the hazards, and design equipment for safe use in such locations.

Mixtures of dispersed combustible materials and oxygen in the air will burn only if the fuel concentration lies within well-defined lower and upper bounds determined experimentally, referred to as flammability limits or explosive limits. Combustion can range in violence from deflagration through detonation.

The pour point of a liquid is the temperature below which the liquid loses its flow characteristics. It is defined as the minimum temperature in which the oil has the ability to pour down from a beaker. In crude oil a high pour point is generally associated with a high paraffin content, typically found in crude deriving from a larger proportion of plant material. That type of crude oil is mainly derived from a kerogen Type III.

<span class="mw-page-title-main">Combustibility and flammability</span> Ability to easily ignite in air at ambient temperatures

A combustible material is something that can burn in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable material catches fire immediately on exposure to flame.

<span class="mw-page-title-main">Fire accelerant</span>

In fire protection, an accelerant is any substance or mixture that accelerates or speeds the development and escalation of fire. Accelerants are often used to commit arson, and some accelerants may cause an explosion. Some fire investigators use the term "accelerant" to mean any substance that initiates and promotes a fire without implying intent or malice.

A flammable liquid is a liquid with flash point of not more than 60.5 °C (141 °F), or any material in a liquid phase with a flash point at or above 37.8 °C (100 °F) that is intentionally heated and offered for transportation or transported at or above its flash point in a bulk packaging.

<span class="mw-page-title-main">Pensky–Martens closed-cup test</span>

The Pensky–Martens closed-cup flash-point test is a test for the determination of the flash point of flammable liquids. It is standardized as ASTM D93, EN ISO 2719 and IP 34 The United States Environmental Protection Agency (EPA) has also published Method 1010A: Test Methods for Flash Point by Pensky-Martens Closed Cup Tester, part of Test Methods for Evaluating Solid Waste, Physical/Chemical Methods, which references the ASTM standard series D93. The Pensky-Martens test is a closed-cup method as opposed to the Cleveland open-cup method.

Lower flammability limit (LFL), usually expressed in volume per cent, is the lower end of the concentration range over which a flammable mixture of gas or vapour in air can be ignited at a given temperature and pressure. The flammability range is delineated by the upper and lower flammability limits. Outside this range of air/vapor mixtures, the mixture can not be ignited. The LFL decreases with increasing temperature; thus, a mixture that is below its LFL at a given temperature may be ignitable if heated sufficiently. For liquids, the LFL is typically close to the saturated vapor concentration at the flash point, however, due to differences in the liquid properties, the relationship of LFL to flash point is not fixed and some spread in the data usually exists.

Breathability is the ability of a fabric to allow moisture vapor to be transmitted through the material.

Reid vapor pressure (RVP) is a common measure of the volatility of gasoline and other petroleum products. It is defined as the absolute vapor pressure exerted by the vapor of the liquid and any dissolved gases/moisture at 37.8 °C (100 °F) as determined by the test method ASTM-D-323, which was first developed in 1930 and has been revised several times. The test method measures the vapor pressure of gasoline, volatile crude oil, jet fuels, naphtha, and other volatile petroleum products but is not applicable for liquefied petroleum gases. ASTM D323-15a requires that the sample be chilled to 0 to 1 degrees Celsius and then poured into the apparatus; for any material that solidifies at this temperature, this step cannot be performed. RVP is commonly reported in kilopascals (kPa) or pounds per square inch (psi) and represents volatization at atmospheric pressure because ASTM-D-323 measures the gauge pressure of the sample in a non-evacuated chamber.

True vapor pressure (TVP) is a common measure of the volatility of petroleum distillate fuels. It is defined as the equilibrium partial pressure exerted by a volatile organic liquid as a function of temperature as determined by the test method ASTM D 2879.

The Cleveland open-cup method is one of three main methods in chemistry for determining the flash point of a petroleum product using a Cleveland open-cup apparatus, also known as a Cleveland open-cup tester. First, the test cup of the apparatus is filled to a certain level with a portion of the product. Then, the temperature of this chemical is increased rapidly and then at a slow, constant rate as it approaches the theoretical flash point. The increase in temperature will cause the chemical to begin to produce flammable vapor in increasing quantities and density. The lowest temperature at which a small test flame passing over the surface of the liquid causes the vapor to ignite is considered the chemical's flash point. This apparatus may also be used to determine the chemical's fire point which is considered to have been reached when the application of the test flame produces at least five continuous seconds of ignition. Temperature range of this apparatus is 120 to 250 degree c

<span class="mw-page-title-main">Petrotest</span>

Anton Paar ProveTec, formerly known as Petrotest GmbH, is a German company within the Anton Paar group that is known for its laboratory equipment for the chemical and petrochemical industries. Furthermore, Anton Paar ProveTec is manufacturing measurement instruments for the cosmetics industry, the aroma and fragrance industry, the food, and pharmaceutical industry. The company was founded in 1873 by Berthold Pensky, who also invented the Pensky-Martens flash point tester. The company is ISO-9001 certified and located south of Berlin in Dahlewitz.

References

  1. Sea Transport of Petroleum, Jansen and Hayes, Ainsley, South Shields 1938
  2. "Use and Storage of Flammable & Combustible Liquids | Environmental Health and Safety | Iowa State University". www.ehs.iastate.edu. Retrieved 2021-11-10.{{cite web}}: CS1 maint: url-status (link)
  3. Jansen and Hyams.pp62
  4. "Standard Test Method for Flash and Fire Points by Cleveland Open Cup Tester", ASTM.org
  5. 1 2 "Ethanol MSDS" (PDF). Nafaa.org. Archived from the original (PDF) on June 17, 2019. Retrieved January 4, 2014.
  6. 1 2 "Coleman Fuel MSDS" (PDF). farnell.com/. Retrieved November 3, 2019.
  7. 1 2 "Flash Point — Fuels". Engineeringtoolbox.com. Retrieved January 4, 2014.
  8. 1 2 "Fuels and Chemicals — Autoignition Temperatures". Engineeringtoolbox.com. Retrieved January 4, 2014.
  9. Buda-Ortins, Krystyna. "Auto-Ignition of Cooking Oils" (PDF). Drum.lib.umd.edu.