What is flash point?

The  “flash point” is  the lowest temperature at which a volatile substance can become vapourised into a flammable gas.

Flash point is analyzed by raising the temperature of a sample material and the same time an ignition source to it, the temperature at which vapour above the sample “flash” (ignite),  and this is  “flash point”.

Why need to test flash point

We need to test flash point, because it is about the Quality Control,Transport and Storage Regulations, CLP Regulations and also Waste Disposal Regulations of the materials and Products.

Flash point requirements are included in many product specifications with various international or national standards, normally meet the ASTM D92,ASTM D93,IP 170,ASTM D56,ASTM D3828 etc. This classifiation is used to warn the risk and provide the support for manufacturing,transporting and storage. Flash point is also a critical parameter used to formulate safety warnings on household cleaning materials,cosmetic and many other products.

Changes in flash point are also used to measure the batch consistency of a material.

Materials Flammability

Extremely flammable: Flash point below 0°C

Highly flammable: Flash point below 21°C

Flammable: Flash point below 55°C

Open and Closed Cup Flash Point Tests

1.Flash point tests fall into two main categories – “open cup” and “closed cup”.

2.Open Cup Flash Point Tests,Open cup tests simulate the potential ignition of liquid spillage in uncontained conditions.In open cup tests the sample cup is not enclosed but heated openly and an ignition source is introduced over its surface at intervals to check for an ignition flash. The flash point will vary according to the distance between the substance and the ignition source so accurate height dimensions are laid down in test methods. Cleveland and Small Scale open cup are the most frequently specified “open cup” test methods.

Closed Cup Flash Point Tests

Closed cup test are generally used as industry standards because the test sample is contained and the ignition source is introduced into the test cup itself. This often better simulates real-life conditions such as those found inside a fuel tank or chemical container.The test results are less affected by laboratory conditions and give a more precise and lower (safer) result which ensures safer practices.

Non-equilibrium and Equilibrium Flash Point Tests

There are two types of closed cup test:

Non-equilibrium Tests – Abel, Pensky-Martens,

Tag and Cleveland

The term non-equilibrium means that the vapour is not in equilibrium with the liquid. Non-equilibrium flash point tests are when the liquid is heated at a steady rate of temperature increase while the ignition source is applied at regular intervals.

Advantages: test instrumentation is univerally available and standardised for a wide range of products.

Disadvantages: each time the flame is dipped, some of the volatile components may escape which can give artificially high flash points and poor precision. The temperature of the liquid and vapour can also vary significantly inside the cup.

Non-equilibrium tests also require a large sample size of 50 to 80ml per test.

Equilibrium Tests

Traditional equilibrium flash point tests use a water bath to heat the sample cup to ensure that the liquid and vapour of the sample are in temperature equilibrium, these tests require careful procedure and necessitate a very slow heating rate.

Small Scale method overcomes these laborious processes by utilising a 2ml or 4ml sample which achieves ‘Rapid Equilibrium’ between the vapour and sample in less than two minutes and gives a reliable flash point result.

Advantages: Improved precision compared to non-equilibrium methods.

Low cost and rapid result.

Flash/no flash result is widely adopted in product specifications.

Only 2ml or 4ml of test sample required.

Which Flash Point Test Method To Use?

The appropriate method for a specific material is typically cited in a product specification or regulation. In certain circumstances a referee test method may be stated, this method should be the first choice.

If a number of alternative test methods are specified then the choice will be influenced by other factors such as sample size requirements, speed of testing or precision and availability of test instrumentation.

When testing for contaminants, certain test methods and procedures are more practical than others and commonly an equilibrium test method is recommended for testing samples that may contain traces of volatile contaminants. The Small Scale flash/no flash method is widely adopted because of its simplicity and small sample volume.

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