(a) This method describes a test procedure for the determination of open-cup flashpoints of volatile flammable materials having flashpoints below 175 °F.

This method, when applied to paints and resin solutions which tend to skin over or which are very viscous, gives less reproducible results than when applied to solvents.

2. The sample is placed in the cup of a Tag Open Tester, and heated at a slow but constant rate. A small test flame is passed at a uniform rate across the cup at specified intervals. The flashpoint is taken as the lowest temperature at which application of the test flame causes the vapor at the surface of the liquid to flash, that is, ignite but not continue to burn.

3. The Tag open-cup tester is illustrated in Fig. 1. It consists of the following parts, which must conform to the dimensions shown, and have the additional characteristics as noted:

Copper bath, preferably equipped with a constant level overflow so placed as to maintain the bath liquid level 1/8-inch below the rim of the glass cup.

Thermometer holder. Support firmly with ringstand and clamp.

Thermometer. For flashpoints above 40 °F., use the ASTM Tag Closed Tester Thermometer, range of + 20 to + 230 °F., in 1 °F. divisions, and conforming to thermometer 9F. of ASTM Standard E 1. For flashpoints from 20 °F. to 40 °F., use ASTM Tag Closed Tester, Low Range, Thermometer 57F. For flashpoints below 20 °F., use ASTM Thermometer 33F. The original Tag Open-Cup (Paper Scale) Thermometer will be a permissible alternate until January 1, 1962. It is calibrated to −20 °F.

Glass test cup. Glass test cup (Fig. 2), of molded clear glass, annealed, heat-resistant, and free from surface defects.

Leveling device. Leveling device or guide, for proper adjustment of the liquid level in the cup (Fig. 3). This shall be made of No. 18-gage polished aluminum, with a projection for adjusting the liquid level when the sample is added to exactly 1/8-inch below the level of the edge or rim of the cup.

“Micro,” or small gas burner of suitable dimensions for heating the bath. A screw clamp may be used to help regulate the gas. A small electric heater may be used.

Ignition taper, which is a small straight, blow-pipe type gas burner. The test flame torch prescribed in the method of test for flash and fire points by Cleveland Open Cup (ASTM designation: D 92) is satisfactory.

Alternative methods for maintaining the ignition taper in a fixed horizontal plane above the liquid may be used, as follows:

Guide wire, 3/32-inch in diameter and 31/2 inches in length, with a right-angle bend 1/2-inch from each end. This wire is placed snugly in holes drilled in the rim of the bath, so that the guide wire is 5/8-inch from the center of the cup and resting on the rim of the cup.

Swivel-type taper holder, such as is used in ASTM METHOD D 92. The height and position of the taper are fixed by adjusting the holder on a suitable ringstand support adjacent to the flash cup.

Draft shield, consisting of two rectangular sheets of noncombustible material, 24 inches × 28 inches, are fastened together along the 28-inch side, preferably by hinges. A triangular sheet, 24 inches × 24 inches × 34 inches is fastened by hinges to one of the lateral sheets (to form a top when shield is open). The interior of the draft shield shall be painted a flat black.

(a) Place the tester on a solid table free of vibration, in a location free of perceptible draft, and in a dim light.

Run water, brine, or water-glycol solution into the bath to a predetermined level, which will fill the bath to 1/8-inch below the top when the cup is in place. An overflow is permissible for water-level control.

Firmly support the thermometer vertically halfway between the center and edge of the cup on a diameter at right angles to the guide wire, or on a diameter passing through the center of the cup and the pivot of the taper. Place so that the bottom of the bulb is 1/4-inch from the inner bottom surface of the cup. If the old Tagliabue thermometer is used, immerse to well cover the mercury bulb, but not the wide body of the thermometer.

Fill the glass cup with the sample liquid to a depth just 1/8-inch below the edge, as determined by the leveling device.

Place the guide wire or swivel device in position, and set the draft shield around the tester so that the sides from right angles with each other and the tester is well toward the back of the shield.

If a guide wire is used, the taper, when passed, should rest lightly on the wire, with the end of the jet burner just clear of the edge of the guide wire. If the swivel-type holder is used, the horizontal and vertical positions to the jet are so adjusted that the jet passes on the circumference of a circle, having a radius of at least 6 inches, across the center of the cup at right angles to the diameter passing through the thermometer, and in a plane 1/8-inch above the upper edge of the cup. The taper should be kept in the “off” position, at one end or the other of the swing, except when the flame is applied.

Light the ignition flame and adjust it to form a flame of spherical form matching in size the 5/52-inch sphere on the apparatus.

Adjust heater source under bath so that the temperature of the sample increases at a rate of 2±0.5 °F. per minute. With viscous materials this rate of heating cannot always be obtained.

5. Determine an approximate flashpoint by passing the taper flame across the sample at intervals of 2 °F. Each pass must be in one direction only. The time required to pass the ignition flame across the surface of the sample should be 1 second. Remove bubbles from the surface of the sample liquid before starting a determination. Meticulous attention to all details relating to the taper, size of taper flame, and rate of passing the taper is necessary for good results. When determining the flashpoint of viscous liquids and those liquids that tend to form a film of polymer, etc., on the surface, the surface film should be disturbed mechanically each time before the taper flame is passed.

6. Repeat the procedure by cooling a fresh portion of the sample, the glass cup, the bath solution, and the thermometer at least 20 °F. below the approximate flashpoint. Resume heating, and pass the taper flame across the sample at two intervals of 2 °F. until the flashpoint occurs.

7. The average of not less than three recorded tests, other than the initial test, shall be used in determining the flashpoint and flammability of the substance.

(a) Make determinations in triplicate on the flashpoint of standard paraxylene and of standard isopropyl alcohol which meet the following specifications:

Specifications for p-xylene, flashpoint check grade. p-xylene shall conform to the following requirements;

Specifications for ispropanol, flash point check grade. Isopropanol shall conform to the following requirements:

Calculate a correction factor as follows:

(a) For hydrocarbon solvents having flashpoints between 60 °F. and 110 °F., repeatability is ±2 °F. and the reproducibility is ±5 °F.

If results from two tests differ by more than 10 °F., they shall be considered uncertain and should be checked. This calibration procedure provided in this method will cancel out the effect of barometric pressure if calibration and tests are run at the same pressure. Data supporting the precision are given appendix III of the 1956 Report of Committee D-1 on Paint, Varnish, Lacquers and Related Products, Proceedings, Am. Soc. Testing Mats., Vol. 56 (1956).

The test apparatus and procedure described in § 1500.43 may be used by manufacturers and labelers of products subject to the Federal Hazardous Substances Act to determine flashpoint temperatures of those products under the conditions set forth in § 1500.3(c)(6)(iv), as amended.