ASTM D93-18: Standard Test Methods for Flash Point by Pensky-Martens Closed Cup Tester details three procedures under a shared method for determining flash point. Basically, this is the temperature in which a liquid can burst into flames.
What is Flash Point?
Flash point is an attribute associated with events far more ferocious and destructive than a simple flash of light. Defined as the lowest temperature of a liquid at which its vapors will form a combustible mixture with air, flash point is a convenient and reliable classification of flammability for numerous petroleum liquids and related substances. Flash point is defined in three main categories in relation to temperature:
Extremely Flammable: Flash point below 0°C
Highly Flammable: Flash point below 21°C
Flammable: Flash point below 55°C
While the methods used for comprehending the flammability of oils, fuels and petroleum-based liquids truthfully need no arguments justifying their existence, flash point is useful for quality control, waste disposal, transport, and other applications.
Pensky-Martens Closed Cup Testing, According to ASTM D93
There are two basic methods for determining the flash point of a volatile liquid: closed cup and open cup. Pensky-Martens is a closed-cup test method, meaning that it aims to simulate a liquid spill in a closed environment. According to ASTM D93-18, Pensky-Martens test procedures can determine the flash point of petroleum products in the 40°C to 370°C range by either manual or automated closed-cup apparatus, as well as determining the flash point of biodiesel in the 60°C to 190°C range by an automated closed-cup apparatus.
ASTM D93-18 officially standardized the Pensky-Martens closed-cup test, and it is referenced by the EPA in SW-846 Test Method 1010A: Test Methods for Flash Point by Pensky-Martens Closed Cup Tester. Under the Pensky-Martens method, a brass test cup of specified dimensions is filled with the petroleum test specimen and heated, and the volatile specimen is stirred at specified rates. An ignition source is directed into the test cup intermittently with simultaneous interruption of the stirring. Once a flash is detected, results are recorded.
In ASTM D93-18, there are three Pensky-Martens Procedures for Flash Point:
Procedure A applies to distillate fuels, including diesel, biodiesel blends, kerosene, heating oil, and turbine fuels. It can also be used with new and in-use lubricating oils
Any other homogenous petroleum liquids not included in the scope of Procedures B or C are applicable to Procedure A.
Procedure B applies to residual fuel oils, cutback residua, used lubricating oils, mixtures of petroleum liquids with solids, petroleum liquids that tend to form a surface film under test conditions, or petroleum liquids of such kinematic viscosity that they are not uniformly heated under the stirring and heating conditions of Procedure A.
Procedure C is applicable to biodiesel. As we discussed in another post, biodiesel or biodiesel blends, which are comprised of mono-alkyl esters of long chain fatty acids and derived from vegetable oils or animal fats, are designated B100 by ASTM D975-18. The flash point of residual alcohol in biodiesel can be difficult to observe by manual flash point techniques. Therefore, ASTM D93-18 states that, for biodiesel, automated apparatus with electronic flash point detection are used exclusively.
Other Methods for Measuring Flash Point
It is noted in the introduction to ASTM D93-18 that “the rate of heating may not in all cases give the precision quoted in the test method because of the low thermal conductivity of some materials,” and that there are, in fact, arc flash point test methods with slower heating rates. ASTM D3941-14: Standard Test Method for Flash Point by the Equilibrium Method With a Closed-Cup Apparatus details the equilibrium method, which also makes use of a closed cup apparatus.
ASTM D93-18: Standard Test Methods for Flash Point by Pensky-Martens Closed Cup Tester is available on the ANSI Webstore.