ISO 3679 Determination of flash point - Rapid equilibrium closed cup method
5 Reagents and materials
5.1 Cleaning solvent
An appropriate solvent for the removal of traces of the previous test portion from the test cup and cover.

NOTE The choice of solvent will depend upon the previous material tested and the tenacity of the residue. Low volatility aromatic (benzene-free) solvents may be used to remove traces of oil, and mixed solvents such as toluene-acetone-methanol may be effective for the removal of gum-type deposits.

5.2 Verification liquids
A series of certified reference materials (CRM) and/or secondary working standards (SWS) as described in Annex C.

6 Apparatus
6.1 General
The apparatus is described in Annex A, and this includes the details of the test cup and cover assembly, together with dimensions and special requirements. These are shown in Figure A.1 to Figure A.5. The measurement of flash points over the whole range of −30 °C to 300 °C may require more than one instrument.

6.2 Syringes
6.2.1 2 ml syringe, adjusted to deliver 2.00 ml +/- 0.05 ml and equipped, if required, with a needle suitable for use with the apparatus at test temperatures up to and including 100 °C. When testing FAME, a 2 ml sample is used at all temperatures.

6.2.2 5 ml syringe, adjusted to deliver 4.00 ml +/- 0.10 ml and equipped, if required, with a needle suitable for use with the apparatus at test temperatures above 100 °C. A 5 ml syringe is not required when testing FAME.

6.3 Barometer, accurate to 0.1 kPa. Barometers precorrected to give sea-level readings, such as those used at weather stations and airports, shall not be used.

6.4 Heating bath or oven (optional), for warming the samples, if required, and capable of controlling the temperature to +/- 5 °C. If an oven is used, it shall be intrinsically safe for hydrocarbon vapours.

It is recommended that the oven be of explosion-protected design.

6.5 Cooling bath or freezer (optional), for cooling the samples, if required, and capable of cooling the sample to 10 °C below the expected flash point, and controlling the temperature to +/- 5 °C. If a freezer is used, it shall be of an explosion-protected design.

6.6 Draught shield (optional), if required to minimize draughts, fitted at the back and on two sides of the instrument.

NOTE A shield, 350 mm high, 480 mm wide and 240 mm deep, is suitable.

6.7 Cup insert (optional). See Annex D.

NOTE For samples that are difficult to remove, a thin metal cup insert can be used.

7 Apparatus preparation
7.1 General
Select the appropriate instrument for the expected flash point temperature. Follow the manufacturer's instructions for the correct set-up and operation of the apparatus. The use of a cup insert (6.7) for potentially adherent materials is described in Annex D.

7.2 Location of apparatus
Support the apparatus (Annex A) on a level and steady surface in a draught-free position.

Use of a draught shield (6.6) is recommended when protection from draughts is not available.

NOTE When testing materials which may produce toxic vapours, the apparatus may be located in a fume hood with an individual control of air flow, adjusted such that the vapours can be withdrawn without causing air currents around the test cup during the test.

7.3 Cleaning of the test cup and accessories
Clean the test cup, cover and its accessories with an appropriate solvent (5.1) to remove traces of gum or residue from the previous test. Follow the manufacturer's instructions for the care and servicing of the instrument.

NOTE 1 A stream of clean dry air may be used to remove the last traces of solvent used.

NOTE 2 The filler orifice may be conveniently cleaned with a pipe cleaner.

7.4 Apparatus verification
7.4.1 Verify the correct functioning of the apparatus at least once a year by testing a certified reference material (CRM) (5.2). The result obtained shall be equal to or less than R/√2 from the certified value of the CRM, where R is the reproducibility of the method (see 13.3).

It is recommended that more frequent verification checks be made using secondary working standards (SWSs) (5.2).

NOTE A recommended procedure for apparatus verification using CRMs and SWSs, and the production of SWSs, is given in Annex C.

7.4.2 The numerical values obtained during the verification check shall not be used to provide a bias statement, nor shall they be used to make any correction to the flash points subsequently determined using the apparatus.

If the instrument fails the verification test, it is recommended that the operator should check that:
a) the cover makes a vapour-tight seal with the test cup;
b) the shutter provides a light-tight seal;
c) adequate heat-transfer paste surrounds the thermometer bulb and immersed portion of the thermometer barrel.