Flash and Fire Points of Bitumen


Definitions:
Flash point is defined as the lowest temperature at which the vapor of the test specimen starts to ignite under the specified conditions of the test.

Fire point is defined as the lowest temperature at which the test specimen will sustain burning for five seconds under the specified conditions of the test.

Significance of the Test
1. Flash point can be used to measure the tendency of the material to catch flames. It is one of the properties which can be used to assess the overall flammability of the material.
2. Flash point is used to class flammable and combustible materials according to safety regulations.
3. Flash point can be used to obtain an idea about the presence of volatile and flammable substances in a, theoretically, non-flammable material.
4. Fire point is used to measure combustibility of the material.

Apparatus and Equipment:
The main apparatus is called the Cleveland Open Cup Apparatus, shown in Figure 8.1. It consists of the following:
1. Test cup.
2. Heating plate.
3. Test flame.
4. Thermometer capable of measuring high temperatures up to 500°C.


Sample Preparation:
1. Make sure that the sample is fluid. If the sample is not fluid, then heat it carefully making sure that the temperature does not exceed 60ºC below the probable flash point.
2. Fill the cup with the sample to the specified level. Take care not to overfill the cup.
3. Air bubbles or foams should be carefully removed. Make sure that the surface is foam or air bubble-free surface before starting the test.
4. If foam could not be removed, then discard the sample completely and prepare a new one.

Test Procedure:
1. Let the apparatus stand on a leveled steady place. Protect from strong sunlight.
2. Wash the test cup carefully using some solvent in order to remove any traces of oils or residuals.
3. Support the thermometer in a vertical position at 6.4 mm from the bottom of the cup. Locate the thermometer halfway between the center and the side of the cup.
4. Fill the cup with the sample to the specified level. Take care not to overfill the cup. Air bubbles or foams should be carefully removed as mentioned earlier.
5. Light the test flame adjusting the flame to a diameter of 3 to 5 mm.
6. Start heating the sample with a relatively high speed (14ºC to 17ºC per minute). Continue until the temperature is about 60ºC below the probable flash point then decrease the heat so that the rate of heating is about 5ºC to 6ºC per minute.
7. When the temperature is about 30ºC below the probable flash point, apply the flame to the sample. The flame should be passed along the center of the sample and also about the circumference in a smooth way. The flame must be at a distance of not more than 2 mm above the plane of the edge of the can. Watch for possible ignition. The passing of the flame across the cup should be in about one second.
8. Repeat step 7 every increase of 2ºC.
9. Record the temperature at which flash ignition occurs. Record this value as the flash point.
10. Continue heating with the same rate (5ºC to 6ºC per minute) and repeat steps 7 and 8.
11. Record the temperature at which ignition occurs and burning continues for a minimum period of 5 seconds. Record this value as the fire point of the tested material.
12. Record the ambient barometric pressure.

Calculations:
Calculate the corrected values of the flash and fire points of the tested samples using the following equations:

Cc= Co + H(AP – P) (1)
where,
Cc = Corrected flash or fire point.
Cc = Observed flash or fire point.
Ap = Barometric pressure at the sea level, which equals 101.3 kPa or 760 Hg.
P = Ambient Barometric pressure.
H = Constant, which equals 0.25 when the pressure is in kPa and 0.033 when the pressure is in Hg.

Comments:
1. The final result should be rounded to the nearest 2ºC.
2. The difference between two successive tests performed by the same operator in the same laboratory should not exceed 8ºC.
3. The difference between two single and independent results performed at different laboratories should not exceed 17ºC for the flash point or 14ºC for the fire point.
4. If the results obtained do not conform to the conditions 2 and 3, the test must be repeated with new samples.
5. The method is suitable for temperatures above 80ºC.

Report:
1. Obtain the average value of the tested samples and judge the acceptability of the results.
2. Why should the apparatus be sheltered from strong sunlight?
3. How is the result affected if air bubbles are present at the surface of the test sample?
4. What would you recommend if the flash point of the sample is expected to be 60ºC?

References:
ASTM D92-90, (2000), “Standard Test Method for Flash and Fire Points by Cleveland Open Cup”.