Flash point testing is a procedure designed to determine whether a sampled mixture of vapour and air is flammable. It can also determine the temperature at which flammability occurs in a sample.
The lowest temperature at which its vapours ignite from an ignition source is the flash point of a material.
Flash point analysis is important for testing various products, including lubricants and petroleum-based materials. The oil industry uses flash point testing for oil analysis.
Process industries routinely use flammable materials. This exposes them to frequent risk of fire and explosion.
To minimise this risk, it is important to test the materials used in processes for their flammability.
These materials will have certain key characteristics:
Flammability testing should account for the different variables which can affect the flammability of a material.
These variables include:
The size and shape of the testing container can also influence flammability in tests.
The data from flammability testing can then help in implementing safety procedures and minimise the threat of fire or explosion.
The major uses of flash point testing are:
In assessing the risk of flammability, flash point analysis is an effective and efficient method.
Essentially, the lower a substance’s flash point temperature, the higher its risk of flammability.
By classifying materials according to this risk, this enables their correct and safe use and storage.
Specifications of different materials will include their flash points to control this flammability risk, and for quality control purposes.
Correct classification of materials, including chemicals containing petroleum, is essential for maintaining up to date safety instructions about packaging, handling and use.
Flash point testing can determine whether a liquid is classifiable as flammable, ignitable or combustible. For example, a liquid with a flash point below ambient temperature will be more hazardous.
If there is a change in flash point in a material, this can indicate that it contains contaminants which could be volatile. Sometimes one material is adulterated by another, and flash point testing will expose this too.
Contaminants can have a significant effect on flash points, especially in those situations where the contaminant is more volatile than the material itself.
Another important use of flash point testing for contamination is in oil analysis.
If diesel or petrol fuel contaminates engine oil, it can act as a thinner, causing the oil’s viscosity to drop dramatically. This viscosity is a key property of engine oil, as it helps protect engine parts against abnormal wear and failure.
A flash point test will indicate the presence of diesel or petrol fuel in engine oil. Used with a viscosity test, it can pinpoint whether oil thinning is due to degradation or contamination.
The flash point of a volatile material is the lowest temperature at which its vapours will ignite.
Liquids will have a specific vapour pressure. Vapour pressure is the measure of the pressure that a gas exerts above a liquid in a sealed container.
For example, if you heat a bottle of water, its vapour, and the amount of pressure, will increase.
Liquids with a substantial vapour pressure at room temperature are classed as volatile.
Vapour pressure is subject to Boyle’s Law. This determines the relationship between the compression and expansion of a gas at a constant temperature.
When you apply an ignition source to the vapour of a material, the lowest temperature at which the material combusts, and keeps burning once you remove the ignition source, is its flash point.
Determining a material’s flash point requires the heating of a sample in a container and then introducing a small flame (the ignition source) above the liquid surface.
There are two main methods for carrying out the flash point test: open cup and closed cup.
Each of these methods may be more appropriate for different applications. Certain products or regulations may specify one method or the other.
The type of product you are testing should be within the scope of the testing method you choose.
Within the two broad open cup and closed cup classes of flash point testing, there are several different techniques.
The open cup method for flash point testing uses a vessel, or container, that is exposed to the outside air.
Once the sample material is placed in the vessel, you then gradually raise its temperature, and pass an ignition source over it, until it flashes and ignites at a certain point.
This is the sample’s flash point.
The most common open cup method is the Cleveland open cup (COC). Other methods include Tag and Setaflash.
Initially, the open cup method for flash testing was developed to assess potential hazards when there were spillages of liquids.
As a method, the open cup test is less precise than closed cup, because vapours are free to escape into the atmosphere, and may be affected by local conditions.
Flash point results from this method may also read higher at temperatures above ambient because of the reduced concentration of vapours compared to closed cup methods.
In the closed cup method, you conduct the test using a vessel, which is sealed off from the outside atmosphere.
You then heat both the vessel and sample, which replicates the effect of accidently introducing an ignition source into a sealed container, such as a gas tank or other storage vessel.
This close approximation of real-life conditions, and the precise nature of the testing, makes the closed cup method ideal for product specifications and regulations.
Closed cup testing will generally produce lower flash points because the contained heat is more likely to make the sample material flammable at an earlier stage.
This delivery of lower results tends to make closed cup methods preferred for industry standards.
It is the common method for testing the fire and flash points of all petroleum products that have a flash point above 79°C.
There are four main closed cup flash point testing methods: Pensky Martens, Abel, Tag and Setaflash.
In manual flash testing, the operator is in control throughout, monitoring, stirring and setting temperatures. The operator determines whether a flash has occurred during the test.
The alternative is automated flash testing, where electronics, software and mechanical actions mimic the operator’s actions. This can reduce operator time and save on resources.
ASTM International is an international standards organisation which develops technical standards for different products, materials, services and systems.
It has a set of flash point standards involving different test methods.
In addition there are various IP and ISO standards covering flash point testing:
There is a broad range of flash testing equipment available, for both open and closed cup methods.
Typically, an open cup flash tester will include a heat source (electric or gas), a liquid bath, thermometer and sample test cup.
A closed cup flash tester will include a vessel with a secure lid, a liquid bath, temperature reader and heat controls.
The different methods of open and closed cup testing are suited for different types of material and applications.
For example, the Setaflash Rapid Flash Tester is available in both open cup and closed cup models and is ideal for quality assurance and environmental compliance testing.
The Automatic Cleveland Open Cup flash point tester determines the flash point and fire point of viscous petroleum products.
There are different ways of testing volatile, flammable materials. Flash point is one, and another is ignition or autoignition point.
There is a key difference between what the two methods measure:
The test for ignition point is different to flash point testing. To test for ignition point, you heat a vessel containing the sample material in an enclosed oven. You the measure the point where there is ignition of the sample.
This test is known as ASTM E659, the standard test method for autoignition.
Which test you choose to apply will depend on the type of material you are testing and its end application.
Flash point testing methods meet the needs of a broad range of industries and applications.
Applications for testing include:
You can also use closed cup flash point testing as a quality control method for storage tanks and delivery containers, and as the basis for safety classifications to meet transport regulations.
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