ISO 3679 Determination of flash point - Rapid equilibrium closed cup method
10 Procedure
10.1 General
10.1.1 Follow the manufacturer's instructions for setting the test temperature to the required flash point temperature.

10.1.2 When testing fatty acid methyl esters (FAME), the flash point detector (A.1.6) shall be used.

10.1.3 Do not apply the test flame to the test portion more than once. Use a new test portion of the sample for each test. After each test, turn off the pilot and test flames using the gas control valve, and when the test cup temperature falls to a safe level, remove the test portion and clean the instrument.

10.1.4 Do not confuse the true flash point with the bluish halo that sometimes surrounds the test flame at applications preceding that which causes the actual flash.

NOTE The optional flash detector (A.1.6) is not affected by the halo, and does not require the operator to closely observe the flash point test.

10.1.5 Record the ambient barometric pressure using a barometer (6.3) in the vicinity of the apparatus at the time of the test.

NOTE It is not considered necessary to correct the barometric pressure reading to 0 °C, although some barometers are designed to make this correction automatically.

10.2 Procedure for flash points up to and including 100 °C and for FAME at all temperatures
10.2.1 Charge a clean and dry syringe (6.2.1), adjusted to a temperature at least 10 °C below the expected flash point, with a 2 ml test portion. Close the sample container immediately after withdrawal to minimize the loss of volatile components.

10.2.2 Carefully transfer the syringe to the filler orifice and discharge the test portion into the test cup by fully depressing the syringe plunger. Remove the syringe.

10.2.3 For solid or semi-solid samples, transfer a mass equivalent to approximately 2 ml directly into the test cup and spread it over the bottom of the cup as evenly as possible.

10.2.4 Start the 1 min timing device (A.1.3). Open the gas control valve and ignite the pilot and test flames. Adjust the test flame to conform to the size of the 4 mm gauge ring. Reset the flash detector (A.1.6) if fitted.

10.2.5 When the audible time signal sounds, apply the test flame by slowly and uniformly opening and then closing the shutter over a period of 2 s to 3 s. Check for a flash (see 10.1.4).

If a continuous luminous flame burns in the orifice when the slide is opened and the test flame is introduced, then the flash point lies considerably below the test temperature. In such cases, a reduction of the test temperature by 10 °C is recommended.

10.2.6 If a flash is observed, repeat the procedure given in 10.2.1 to 10.2.5 with a fresh test portion, starting at a temperature 5 °C lower than that at which the flash was observed. If a flash is still observed at this lower temperature, lower the temperature a further 5 °C and repeat again. Repeat until no flash is observed.

10.2.7 If no flash is observed, repeat the procedure given in 10.2.1 to 10.2.5 with a fresh test portion, starting at a temperature 5 °C higher than that at which the last test portion was tested. Repeat tests at 5 °C higher intervals until a flash is observed.

10.2.8 Repeat the procedure given in 10.2.1 to 10.2.5, using a fresh test portion for each test, at 1 °C intervals, starting at the lower of the intervals 5 °C apart established in 10.2.6 and 10.2.7, until a flash is observed. Record the temperature on the thermometer as the observed flash point using 1 °C intervals. If improved sensitivity is required, test a fresh test portion at a temperature 0.5 °C below that at which a flash was observed using 1 °C intervals. If no flash is observed, then the temperature recorded using 1 °C intervals is the observed flash point to the nearest 0.5 °C. If a flash is observed, then this new reading is the observed flash point.

10.3 Procedure for flash points above 100 °C [except when testing FAME (see 10.2)]
10.3.1 Charge a clean and dry syringe (6.2.2) with a 4 ml test portion. Close the sample container immediately after withdrawal to minimize the loss of volatile components.

10.3.2 Carefully transfer the syringe to the filling orifice and discharge the test portion into the test cup by fully depressing the syringe plunger. Remove the syringe.

10.3.3 For solid or semi-solid samples, transfer a mass equivalent to approximately 4 ml directly into the test cup and spread it over the bottom of the cup as evenly as possible.

10.3.4 Start the 2 min timing device (A.1.3). Open the gas control valve and ignite the pilot and test flames. Adjust the test flame with the pinch valve to conform to the size of the 4 mm gauge ring. Reset the flash detector (A.1.6) if fitted.

10.3.5 Carry out the procedure described in 10.2.5 to 10.2.8 and record the observed flash point.

11 Calculation
11.1 Conversion of barometric pressure reading
If the barometric pressure reading is measured in a unit other than kilopascals, convert to kilopascals using one of the following equations:
Reading in hPa x 0.1 = kPa
Reading in mbar x 0.1 = kPa
Reading in mmHg x 0.1333 = kPa

11.2 Correction of observed flash point to standard atmospheric pressure
Calculate the flash point corrected to a standard atmospheric pressure of 101.3 kPa, Tc, using the following equation:
Tc = To + 0.25(101.3 - p)
where
To is the observed flash point at ambient barometric pressure, expressed in degrees Celsius;
p is the ambient barometric pressure, expressed in kilopascals.

NOTE This equation is strictly correct only within the barometric pressure range from 98.0 kPa to 104.7 kPa.