FLASH AND FIRE POINT TEST (ASTM D92)
1. Introduction
The flash point of a volatile liquid is the lowest temperature at which it can vaporize to form an ignitable mixture in air. Measuring a liquid's flash point requires an ignition source. At the flash point, the vapor may cease to burn when the source of ignition is removed. The flash point is not to be confused with the auto ignition temperature, which does not require an ignition source. The fire point, a higher temperature, is defined as the temperature at which the vapor continues to burn after being ignited. Neither the flash point nor the fire point is related to the temperature of the ignition source or of the burning liquid, which are much higher. The flash point is often used as a descriptive characteristic of liquid fuel, and it is also used to help characterize the fire hazards of liquids. “Flash point” refers to both flammable liquids and combustible liquids. There are various standards for defining each term. Most chemists agree that liquids with a flash point less than 60.5°C (141°F) or 37.8°C (100°F) — depending upon the standard being applied — are flammable, and liquids with a flash point above those temperatures are combustible.
Every liquid has a vapor pressure, which is a function of that liquid's temperature. As the temperature increases, the vapor pressure increases. As the vapor pressure increases, the concentration of evaporated flammable liquid in the air increases. Hence, temperature determines the concentration of evaporated flammable liquid in the air. Each flammable liquid requires a different concentration of its vapor in air to sustain combustion. The flash point of a flammable liquid is the lowest temperature at which there will be enough flammable vapour to ignite when an ignition source is applied.
There are two basic types of flash point measurement: open cup and closed cup. In open cup devices the sample is contained in an open cup which is heated, and at intervals a flame is 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). There are two types of closed cup testers: non-equilibrium, such as Pensky-Martens where the vapors above the liquid are not in temperature equilibrium with the liquid, and equilibrium, such as Small Scale (commonly known as Seta flash) where the vapors 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) and are a better approximation to the temperature at which the vapor pressure reaches the lower flammable limit (LFL). 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 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.
Flash Point – The flash point of a material is the lowest temperature at which the application of
test flame causes the vapors’ from the material to momentarily catch fire in the
form of a flash under specified conditions of the test.
Fire Point – The fire point is the lowest temperature at which the application of test flame
causes the material to ignite and burn at least for 5 seconds under specified
conditions of the test.
2. Objective
This experiment is to obtain the temperature level of the asphalt materials for flash and fire point. This is to know its optimum temperature level. The flash point of cutback asphalt is generally determined by use of a Tagliabue Open Cup apparatus, whereas the Cleveland Open Cup is used for flash point determination on other asphaltic materials.
3. Apparatus
a. Cleveland Open Cup Apparatus:
- This apparatus consist of the cup, heating plate, test flame applicator, heater and support.
Figure 3.a: Cleveland Open Cup Apparatus
b. Shield:
- A shield 460 mm (18 in) square and 610 mm (24 in) high and having an open front is recommended.
c. Thermometer:
- A thermometer having a range – 6 to + 400ºC and conforming to the requirements prescribed in specification.
Figure 3.c: Thermometer
4. Methodology
a. First, the cup filled at any convenient temperature so that the top of the meniscus is exactly at the filling line.
b. Then light the test flame and adjust it to a diameter of 3.2 to 4.8 mm (1/8 to 3/16 in.), the size of the comparison bead if one is mounted on apparatus.
c. Heat initially are applied, the rate of temperature rise of the sample is to 25ºF to 30ºF (14ºC to 17ºC)/min. When the sample temperature is approximately 100ºF (56ºC) below anticipated flash point, decrease the heat so that the rate of temperature rise for the last 50ºF (28ºC) before the flash point is 9ºF to 11ºF (5ºC to 6ºC)/min.
d. At least at 50ºF (28ºC) below the flash point start, the test flame are applied when the temperature read on the thermometer reached each successive 5ºF (2ºC) mark. The test flame is passed across the center of the cup, at right angles to the diameter, which passed through the thermometer. With a smooth continuous motion applied the flame either in straight line or along the circumference of a circle having a radius of at least 150 mm (6 in). The center of the test flame must move in horizontal plane not more than 2 mm (5/64 in) above the plane of the upper edge of the cup and passing in one direction only. At the time of the next test flame application, the flame passed in the opposite direction. The time consumed in passed the test flame across the cup in each case shall be about 1 s.
e. The observed flash point the temperature read on the thermometer when a flash appears at any point on the surface of the bluish halo that sometimes surrounds the test flame recorded.
f. The fire point determined and continue heating so the sample temperature increased at a rate of 9ºF to 11ºF (5ºC to 6ºC)/min. the application of the test flame at 5ºF (2ºC) intervals until the oil ignites. Fire point of the oil is observed.
Result
| Point | Temperature (ºC) |
| Flash Point (ºC) | 295 |
| Fire Point (ºC) | 350 |
5. Discussion
Safety procedures must be followed when using a flash tester. Fire extinguishers, safety visors and breathing apparatus should all be available. Draught prevention is important as toxins such as PCBs can be produced during heating. Automated equipment will prevent any potential health risk to the user.
6. Recommendations
Correct sampling is essential for consistent flash point results. Standardized procedures exist which must be followed precisely otherwise partial degassing or complete loss of the ignitable vapors will occur by evaporation. These vapor fractions are the ones with the lowest flash point.
To prevent fractions with low boiling points being lost from large samples sealed containers and cool storage must be used.
7. Conclusions
The sample is heated at a slow, constant rate. A small flame is directed into the cup. The flash point has endured the test of time. In many applications of used oil analysis the flash point test remains the method of choice in detecting certain contaminants and non-conforming lubricant conditions. In other cases the flash point serves as a dependable diagnostic tool or confirming test when a suspect condition has already been flagged. And, like most everything in the world of oil analysis, success in using the flash point depends on the careful adherence to such things as sample handling and test protocol.
8. References
a. Muniandy R., Radin Umar Radin Sohadi. Highway Materials, A Guide Book For Beginners. University Putra Malaysia: Penerbit Universiti Putra Malaysia; 2010.
b. Paul H.W., Karen K.D. Highway Engineering [Seventh Edition]. USA: John Wiley & Son; 2003.
c. Mu’men.T.A., Penetration, Softening, Flash and Fire Point, Ductility, Viscosity,& Lost in Heat. 1 (5): [10 screen]. Available from: URL: http://www.ahm531.com/lab-reports/highway-lab/reports/1/Pentration%20&%20Ring%20&%20Ball%20&%20Ductility%20&%20Flash%20&%20Fire%20point.pdf
d. Jim.F., The Enduring Flash Point Test. 1 (4): [4 screen]. Available from: URL: http://www.machinerylubrication.com/Read/19/flash-point-test
e. Flash Point Testing: A User’s Guide. 1 (4): [4 screen]. Available from: URL: http://www.petrotest.com/media/en/Petrotest_Reports_Flashpoint_Testing.pdf
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