⛽ Flash and fire points — the Cleveland open cup method
In short
Heating of the sample in an open cup (5–17 °C/min, then 5–6 °C/min) and passing of a test flame every 2 °C; the flash point 79–400 °C and the fire point (a flame lasting ≥ 5 s), corrected to 101. The test is performed according to PN-EN ISO 2592:2017-10; Range: Open cup flash point 79–400 °C (diesel and heating oils — the closed cup, ISO 2719). The procedure comprises 8 steps (about 0 min in total); it is used for: Lubricating, gear, hydraulic and transformer oils — classification and quality control, Diagnostics of engine oils in service (dilution with fuel, degradation), Bitumens and bituminous binders (the open cup flash point).
At a glance
- Standard: PN-EN ISO 2592:2017-10
- Category: Petrochemistry
- Procedure steps: 8
- Total time of stages: 0 min
- Range: Open cup flash point 79–400 °C (diesel and heating oils — the closed cup, ISO 2719)
- Rate of heating: 5–17 °C/min at first; 5–6 °C/min through the last 28 °C before the expected flash point
- Test flame: Diameter 3.2–4.8 mm; passed in (1 ± 0.1) s, ≤ 2 mm above the rim of the cup; the first application 28 °C before the expected value, then every 2 °C
Overview
The standard specifies the procedure for determining the flash and fire points of petroleum products with the Cleveland open cup apparatus; it applies to products with an open cup flash point from 79 °C to 400 °C, except for diesel and heating oils, which are most often tested in a closed cup according to ISO 2719. The flash point is the lowest temperature of the sample, corrected to a pressure of 101.3 kPa, at which the application of a test flame causes the vapours of the sample to ignite under the prescribed conditions; the fire point is the lowest temperature at which the vapours ignite and burn for at least 5 s. The 2017 edition added among other things a procedure for determining the approximate flash point for a sample whose expected value is unknown (in accordance with ASTM D92).
The flash point is an important parameter for the classification of flammable liquids: the regulation of the Polish Minister of the Interior and Administration of 7 June 2010 divides them into liquids with a flash point up to 21 °C, above 21 °C up to 55 °C and above 55 °C up to 100 °C. The Cleveland method serves especially for engine, gear and transformer oils (heating oils are not covered by the standard — see the scope above); in the diagnostics of oils in service a fall of the flash point indicates dilution with fuel, mixing or cracking.
In disputed cases the deciding test is the manual determination; automatic apparatus is permissible when agreement with the precision of the standard has been shown and when the cup and the flame applicator meet the requirements of Annex A. Precision: flash point r = 8 °C, R = 18 °C; fire point r = 8 °C, R = 14 °C.
Method principle
The cup is filled with the sample to the prescribed level. The temperature of the sample may at first be raised rapidly (5–17 °C/min) and, as the flash point is approached, slowly and steadily (5–6 °C/min). At prescribed intervals of temperature a small test flame is passed over the cup. The lowest temperature at which the application of the flame causes the vapours above the surface of the liquid to ignite is the flash point at the ambient pressure; for the fire point the test is continued until the vapours ignite and burn for at least 5 s. Both temperatures are corrected to the standard pressure: tc = td + 0.25·(101.3 − p), where p is the absolute pressure in kPa (the formula has been checked down to 82.0 kPa; 4 kPa corresponds to about 1 °C).
Applications
- Lubricating, gear, hydraulic and transformer oils — classification and quality control
- Diagnostics of engine oils in service (dilution with fuel, degradation)
- Bitumens and bituminous binders (the open cup flash point)
- Classification of flammable liquids for fire protection and transport purposes
- Determination of the fire point of products with a high flash point
Key parameters
| Parameter | Value |
|---|---|
| Range | Open cup flash point 79–400 °C (diesel and heating oils — the closed cup, ISO 2719) |
| Rate of heating | 5–17 °C/min at first; 5–6 °C/min through the last 28 °C before the expected flash point |
| Test flame | Diameter 3.2–4.8 mm; passed in (1 ± 0.1) s, ≤ 2 mm above the rim of the cup; the first application 28 °C before the expected value, then every 2 °C |
| Fire point | The vapours burn for ≥ 5 s; further heating at 5–6 °C/min, the flame every 2 °C |
| Correction for pressure | tc = td + 0.25·(101.3 − p); an absolute barometer with an accuracy of 0.5 kPa and a resolution of 0.1 kPa |
| Precision | Flash point: r = 8 °C, R = 18 °C; fire point: r = 8 °C, R = 14 °C; the result to 1 °C |
Standard
- Standard number
- PN-EN ISO 2592:2017-10
- Title (PL)
- Przetwory naftowe i produkty podobne — Oznaczanie temperatury zapłonu i palenia — Metoda otwartego tygla Clevelanda
- Title (EN)
- Petroleum and related products — Determination of flash and fire points — Cleveland open cup method
Step-by-step procedure
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Sampling and storage of the sample
Take the sample according to ISO 3170/ISO 3171, in a tight container filled to 85–95 %; store it below 30 °C, limiting the loss of vapours. Take the sub-sample at a temperature at least 56 °C below the expected flash point; decant samples with free water, mix liquid samples gently and warm solid and semi-solid ones in the container to no higher than 56 °C below the expected flash point.
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Preparation of the apparatus
Set the apparatus on a level, stable surface in a room free of draughts (the shield; with toxic vapours — a fume hood with a control that gives no movement of air over the cup), shielded from strong light. Wash the cup with solvent, dry it with a stream of air and remove carbon deposits with steel wool; cool the cup to at least 56 °C below the expected flash point. Fix the thermometer with the bottom of the bulb (6.4 ± 0.5) mm above the bottom of the cup, halfway between the centre and the wall, on the side opposite the applicator.
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Filling
Record the absolute barometric pressure. Fill the cup so that the top of the meniscus is at the filling mark; remove any excess with a pipette (sample outside the apparatus — empty it, clean it and fill it again); remove bubbles and foam (foam persisting in the final stage — reject the result). Set the cup centrally on the heating plate.
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The flame and the preliminary heating
Light the test flame and set its diameter to 3.2–4.8 mm; before the heating pass the flame over the sample to check for unexpected volatile constituents, then try for ignition every 10 °C, up to 56 °C before the expected flash point. Heat at a rate of 5–17 °C/min, and from about 56 °C before the expected flash point reduce the heating so that through the last 28 °C the rise is 5–6 °C/min. Do not disturb the vapours over the cup by movement or by breathing.
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Application of the flame
From a temperature 28 °C below the expected flash point pass the flame in one smooth movement in (1 ± 0.1) s across the centre of the cup, at right angles to the diameter through the thermometer, in a straight line or an arc of radius ≥ 150 mm, no higher than 2 mm above the rim of the cup; make the successive applications in the opposite direction, at temperatures that are multiples of 2 °C. Push any skin that forms aside with a spatula (a skin that is not removed raises the result).
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Reading of the flash point
Record as the detected flash point the temperature of the sample at which the application of the flame causes the vapours to ignite at any point of the surface and a large flame to spread across the surface; do not confuse it with the bluish halo around the test flame. If ignition occurred at the first or at a preliminary application — repeat on a fresh portion with an expected value lower by ≥ 28 °C. A sample of unknown value: start at ≤ 50 °C, apply the flame from 5 °C above the initial temperature, heat at 5–6 °C/min and try every 2 °C — the result is approximate, use it as the expected value in the proper test.
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Fire point
After the flash point has been determined, continue heating at 5–6 °C/min, applying the flame every 2 °C, until the vapours ignite and burn for at least 5 s; record the fire point. Extinguish a flame lasting longer than 5 s with the cover with the handle.
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Calculation and test report
Convert the pressure to kPa (hPa × 0.1; mbar × 0.1; mmHg × 0.1333) and correct: tc = td + 0.25·(101.3 − p); give the flash point and, if need be, the fire point to 1 °C, a reference to the standard, the identification of the product, information on the use of Annex D, any departures and the date.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Cleveland open cup apparatus | Manual or automatic, the cup and the flame applicator according to Annex A of the standard; a sample of about 100 ml (Ecol) | — |
| Shield | Covering at least three sides of the cup (it may be built in) | — |
| Instrument for measuring the temperature | A glass or electronic thermometer with the accuracy and response time of Annex B; the bottom of the bulb (6.4 ± 0.5) mm above the bottom of the cup | — |
| Barometer | Absolute pressure, accuracy 0.5 kPa, resolution 0.1 kPa; do not use barometers corrected to sea level | — |
| Extinguishing cover | Of metal or of a refractory material, with a handle (figure A.2), for extinguishing the flame after the determination of the fire point | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Cleaning solvent | — | For removing traces of the sample from the cup and the cover; for oils, aromatic solvents of low volatility (without benzene), for resinous deposits, mixed solvents |
| Verification liquids | — | A certified reference material (CRM) or secondary working standards (SWS) for the annual verification of the apparatus (the result within R/√2 of the certified value) |
| Steel wool | — | For removing carbon deposits without damaging the cup |
Health and safety (OHS)
- Very high temperatures of the sample and of the heating plate — the sample may spit, foam and smoke; at the fire point the flame is sometimes large and hard to put out — keep the extinguishing cover at hand, wear a face shield
- Before heating, check with the flame for the presence of unexpected volatile constituents
- Test samples with toxic vapours in a fume hood with a flow control that gives no draught over the cup; do not exceed 30 °C when storing samples
- Cleaning solvents (aromatic) — work in a fume hood, with no naked flame
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 2592:2017-10 — “Petroleum and related products — Determination of flash and fire points — Cleveland open cup method”.
How does this method work?
The cup is filled with the sample to the prescribed level. The temperature of the sample may at first be raised rapidly (5–17 °C/min) and, as the flash point is approached, slowly and steadily (5–6 °C/min).
What is the measuring range and accuracy?
Range: Open cup flash point 79–400 °C (diesel and heating oils — the closed cup, ISO 2719); Rate of heating: 5–17 °C/min at first; 5–6 °C/min through the last 28 °C before the expected flash point; Test flame: Diameter 3.2–4.8 mm; passed in (1 ± 0.1) s, ≤ 2 mm above the rim of the cup; the first application 28 °C before the expected value, then every 2 °C; Fire point: The vapours burn for ≥ 5 s; further heating at 5–6 °C/min, the flame every 2 °C.
How long does the test take?
The times given for the individual stages add up to approximately 0 min. The procedure comprises 8 steps.
What equipment is required?
Cleveland open cup apparatus, Shield, Instrument for measuring the temperature, Barometer, Extinguishing cover.
Where is this test used?
Lubricating, gear, hydraulic and transformer oils — classification and quality control; Diagnostics of engine oils in service (dilution with fuel, degradation); Bitumens and bituminous binders (the open cup flash point); Classification of flammable liquids for fire protection and transport purposes; Determination of the fire point of products with a high flash point.
What safety precautions apply?
Very high temperatures of the sample and of the heating plate — the sample may spit, foam and smoke; at the fire point the flame is sometimes large and hard to put out — keep the extinguishing cover at hand, wear a face shield; Before heating, check with the flame for the presence of unexpected volatile constituents; Test samples with toxic vapours in a fume hood with a flow control that gives no draught over the cup; do not exceed 30 °C when storing samples; Cleaning solvents (aromatic) — work in a fume hood, with no naked flame.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 2592.