What is the Temperature at Which a Liquid Continuously Gives Off Vapors

Flash Point

The flash point is the lowest temperature at which a volatile substance evaporates to form an ignitable mixture with air in the presence of an igneous source and continues burning after the trigger source is removed.

From: Experimental Organic Chemistry , 2016

Fuels

E. Lois , ... A.K. Gupta , in Encyclopedia of Physical Science and Technology (Third Edition), 2003

III.G.7 Flash Point

Flash point is a significant property not for the operability of a diesel fuel, but for its storage and handling. Diesel fuels are classified as nonvolatile fuels, and their storage does not need specific precautions. Flash point is an excellent indication of diesel fuel contamination with more volatile products.

Flash point of diesel fuels is measured according to ASTM D 93—Flash-Point by Pensky-Martens Closed Cup Tester. The sample is stirred and heated at a slow, constant rate in a closed cup. At specific temperature intervals (1 or 2   °C), the cup is opened and an ignition source is moved over the top of the cup. The flash point is the lowest temperature at which the application of the ignition source causes the vapors above the liquid to ignite.

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Cleaning with Solvents

John B. Durkee , in Developments in Surface Contamination and Cleaning (Second Edition), 2008

11.3.1.1 Flash Point

The flash point of a solvent has no direct effect on its capability as a cleaning solvent. It does, however, have a dominant indirect effect on selection of the cleaning process, cleaning equipment, and cleaning procedures, as well as packaging, transportation, selection, and disposal. In other words, specifications for the above issues all incorporate flash point. Other than solvency, there is no more important parameter than flash point in solvent cleaning.

"Flash point" is the minimum temperature at which a liquid gives off vapor within a test vessel in sufficient concentration to form an ignitable mixture with the air near the surface of the liquid. The lower the flash point, the easier it is to ignite a liquid solvent. Specific details about how to measure flash point are found in OSHA Standard 1910.106. ³⁸

Measurement of flash point does not require production of a stable flame, just ignition of vapor and fuel. The actual measurement which defines ignition is usually a temperature rise produced by the combustion.

11.3.1.1.1 Flash Point Test Equipment

Flash point test equipment has been designed to simulate the various ways in which solvents are used. Four types are described in Table 11.12. One type of equipment is shown in Figure 11.5.

Table 11.12. Comparison of Flash Point Test Equipment

Name	Test Fluids	Temperature Range (°C)	Cup Open/Closed	Detection Method	ASTM Test	Ignition Source
Tag	Cleaning solvents, etc.	–20 to +   80	Open/closed	Temperature rise	D1310 39 (open), D56-02 40 (closed)	Gas or electric igniter
Setaflash	Diesel, kerosene, lacquers	0–220	Open/closed	Visual	D3278–82 (closed)
Pensky-Martens (shown in Figure 11.5)	Paints, coatings	60–360	Closed	Temperature rise	D 93
Cleveland	Oils, bitumens	>   360	Closed	Ionization detection	D 92

Figure 11.5. Pensky–Martens closed cup tester with mixer for determining the flash point of viscous paints.

The majority of solvent cleaning work is performed in equipment of two types relative to flash point, either an open tank or a closed tank.

An open tank would typically be used for cleaning at less than the boiling point (cold cleaning). The potential for ignition of solvents in cold cleaning, under shipment, or storage conditions is assessed by measuring flash point in an open cup tester.

A closed tank would include a storage or shipping container, or an enclosed machine. In this sense, a vapor degreaser is a closed tank. The potential for ignition of closed tank solvents under cold cleaning conditions is assessed by measuring flash point in a closed cup tester.

Flash points are determined experimentally by heating the liquid in a container (cup) and then introducing a small flame just above the liquid surface. The temperature at which there is a flash/ignition is recorded as the flash point.

Obviously, the same solvent will give different absolute results, and may give different results relative to another solvent, if tested in an open cup or a closed cup tester. The closed-cup method prevents vapors from escaping. The open cup tester, on the other hand, will lose the most volatile components. Thus, open-cup flash points are higher than those for the same solvent measured in the closed cup tester. When several values are available, the lowest temperature is usually taken in order to assure safe operation of the process.

Do not ever accept flash point information if the type of tester is not specified as well. Flash points for cleaning solvents are normally measured by the TAG closed cup test (named for Giuseppe Tagliabue, who developed it). The TAG test is also referred to as "Tag CC," "TAG CC," or simply "CC," for "closed cup."

11.3.1.1.2 Regulatory Requirements Related to Flash Point

Three U.S. government agencies and one private agency have requirements for users of cleaning solvents, based on the flash point of the solvent used. Again, these requirements have at least as much effect on the choice of cleaning solvent as does its solvency power.

These requirements are defined in a classification system which is published in OSHA Standard 1910.106. ³⁸

•

Class IA—Flash Point less than 73   °F (22.7   °C); Boiling Point less than 100   °F (37.8   °C)

•

Class IB—Flash Point less than 73   °F; Boiling Point equal to or greater than 100   °F

•

Class IC—Flash Point equal to or greater than 73   °F, but less than 100   °F

•

Class II—Flash Point equal to or greater than 100   ° F, but less than 140   °F (60   °C)

•

Class IIIA—Flash Point equal to or greater than 140   °F, but less than 200   °F (93.3   °C)

•

Class IIIB—Flash Point equal to or greater than 200   °F

This information is collected in Figure 11.6.

Figure 11.6. Classes of flammable and combustible liquids as defined in 29 CFR-1910.106. ³⁸

Note that boiling point is used only to distinguish between Class IA and Class IB solvents. Class IA liquids are extremely volatile, but there are few liquids that are so classed.

Theoretically, there is no upper limit to Class IIIB, except that liquids with a closed cup flash point above 200   ° F dry slowly and are poor choices for cleaning solvents used in vapor degreasing operations.

The U.S. Department of Transportation (DOT) has a classification system that is only slightly different. Because they are partners in a worldwide network of regulations about hazardous materials, DOT has changed its definition of "flammable liquid" by raising the upper limit to 141   °F (60.5   °C). However, DOT regulations include a so-called "domestic exemption" that allows a shipper to redesignate as a combustible solvent any solvent whose flash point is in the NFPA Class II range and which does not meet any other hazardous material definition.

Note that this classification applies to all liquids, not just liquids used for cleaning, and that the closed cup method is used for all determinations of flash point.

11.3.1.1.3 Flash Point Data

Data from a variety of non-halogenated (i.e. not containing fluorine, bromine, or chlorine atoms) solvents are shown in Table 11.13. ⁴¹ Solvents commonly used for cleaning are printed in boldface type. Data are sorted by flash point value and the National Fire Protection Association (NFPA) classification is differentiated by the shaded background.

Table 11.13. Flash Point Data for Solvents

Chemical	Flash Point		Boiling Point		NFPA Class
	° F	°C	°F	°C
Propane	(157)	(105)	(44)	(42)	IA
Pentane	(57)	(49)	97	36	IA
Ethyl ether	(49)	(45)	95	35	IA
Acetaldehyde	(38)	(39)	69	21	IA
Dimethyl sulfide	(36)	(38)	99	37	IA
Carbon disulfide	(22)	(30)	115	46	IB
Ethylene oxide	(20)	(29)	55	13	IA
n-Hexane	(7)	(22)	156	69	IB
Acetone	(4)	(20)	56	133	IA
Cyclohexane	(4)	(20)	179	81	IB
Tetrahydrofuran	6	(14)	153	67	IB
Benzene	12	(11)	176	80	IB
Triethylamine	20	(7)	193	89	IB
Methyl ethyl ketone (MEK)	25	(4)	176	80	IB
Toluene	40	4	231	111	IB
Methyl alcohol	52	11	149	65	IB
Isopropyl alcohol (IPA)	53	12	180	82	IB
Ethyl alcohol	55	13	173	78	IB
Pyridine	68	20	239–241	116	IB
2-Nitropropane	75	24	248	120	IC
Tert butyl isocyanate	80	27	185–187	85–86	IC
Chlorobenzene	82	28	270	132	IC
Epichlorohydrin	88	31	239–243	115–117	IC
Xylene	81–90	27–32	280–291	138–144	IC
Morpholine	100	38	263	128	II
Acetic acid, glacial	103	39	244	48	II
Bromobenzene	118	48	307–316	153–158	II
Formic acid	122	50	213	101	II
Methyl lactate	135	57	291	144	II
Stoddard solvent	100–140	38–60	300–400	150–200	II
Iso-propyl lactate	140	60	315	157	II
Ethyl lactate	142	61	307	153	IIIA
Benzaldehyde	145	63	352	178	IIIA
Cyclohexanol	154	68	322	161	IIIA
Tetrahydronaphthalene	160	71	406	208	IIIA
Iso-butyl lactate	169	76	360	182	IIIB
Methacrylic acid	170	77	316	158	IIIA
Butyl lactate	174	79	369	187	IIIB
Nitrobenzene	190	88	412	211	IIIA
n-Methyl pyrrolidone	199	93	396	202	IIIA
Benzyl alcohol	213	101	401	205	IIIB
Caproic acid	215	102	400	204	IIIB
Ethylene glycol	232	111	388	198	IIIB
3-Ethyllhexyl lactate	235	113	475	246	IIIB
Phenyl ether	239	115	498	258	IIIB
Stearic acid	385	196	726	386	IIIB

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Chemistry and Physics of Fire and Liquid Fuels

Eric Stauffer , ... Reta Newman , in Fire Debris Analysis, 2008

4.6.6 Flash Point

The flash point of a liquid is defined as the lowest temperature at which a substance generates a sufficient amount of vapor to form a (vapor/air) mixture that can be ignited (piloted ignition). At that temperature, the vapor pressure of the liquid provides a vapor concentration that equal to the lower flammability limit. If ignition is attempted when the liquid reaches its flash point, a flash flame will occur but the flame will not sustain. The cloud will burn and the fire will self-extinguish because the energy released by the combustion and transferred to the remaining fuel is not sufficient to produce enough vapors to sustain the flame.

The flash point is an important concept in fire investigation and fire protection because it is the lowest temperature at which a risk of fire exists with a given liquid. It is crucial in many circumstances to establish the presence of some liquids and to know their flash point during the investigation process.

Flash points usually are found in the literature. MSDS ⁸ are particularly good resources for flash point values of commercial chemicals and products. As a general rule for hydrocarbons, the simpler the molecule, the lower the flash point. Although some equations have been developed to calculate flash point, their utility is limited due to significant variations in their accuracy.

Calculating Flash Points

The following formula allows for the calculation of flash points [41]:

$\frac{1000}{T_F\text{undefined}+\text{ 273}}\text{ =}{B}_0\text{ +}{B}_1\cdot {\log }_{10}{P}_{25}$

T_F = Flash point

B₀ and B₁ = constant (see table below) P₂₅ = Vapor pressure of liquid at 25°C

This particular calculation is, unfortunately, not very accurate (variation with measured values can be as high as

100°C!) and requires the knowledge of the constants in Table 4-8 as well as the knowledge of the vapor pressure of the compound. Another more simplistic mathematical calculation starts with the autoignition temperature (AIT) in degrees Celsius of the compound [41]. It is shown in Table 4-9.

Table 4-8. Constants for flash point calculations [41]. (*These values produce more accurate results and were obtaned by excluding 2,2-dimethylbutane, naphthalene, dodecane, diphenylmethane, tetradecane, nonylbenzene, and decylbenzene.)

Class	B0	B1
Acetates	2.976	0.380
Acids	2.777	0.491
Alcohols	2.953	0.323
Phenols	2.953	0.323
Aldehydes	2.924	0.443
Alkanes	3.142	0.319
Alkanes*	2.948	0.470
Aromatics	3.142	0.319
Aromatics*	2.948	0.470
Alkenes	3.097	0.424
Amines	3.077	0.322
Esters	2.948	0.385
Ethers	3.056	0.357
Ketones	3.033	0.381

Table 4-9. Calculations of flash point [41].

Class	Flash point [°C]
Paraffinic hydrocarbons and olefins in gaseous state at NTP	350 – AIT
Paraffinic hydrocarbons and olefins in liquid state at NTP	250 – AIT
Benzene series	550 – (AIT + K)
Alcohols (MW ≤ 60)	8 + nHr
Alcohols (60 < MW ≤ 88)	11 + 2nHr
Alcohols (MW > 88)	29 + 3nHr

K = a variant (9 for each first branch CH₃ and 21 for each second branch CH₃, 16 for each first branch CH and 12 for each second branch CH2)

nHr = number of hydrogen in radicals

Flash point values found in the literature are the result of measurements made in the laboratory at equilibrium, via a standard test method. Chapter 14 provide more detailed descriptions for determining flash points by laboratory tests. Flash point values for a given chemical or product may vary depending on the measurement technique used. It is important to understand that these conditions might not be reproduced in a particular practical situation, and the flash point values cannot always be applied per se.

When a liquid is composed of a mixture of different chemicals, such as gasoline, the flash point of the mixture will be strongly influenced by the flash point of the components having the lowest flash point [42, 43]. This is due to the distribution of the components of the mixture in the vapor, which is dependent on their vapor pressure, as previously described.

Flash point is an important concept in fire investigation and fire debris analysis, not only for the classification of the ignitable liquids, but also for the evaluation of hazardous situations. The National Fire Protection Association (NFPA) defines a liquid with a flash point below 100°F (37.8°C) as flammable, and a liquid with a flash point equal to or above 100°F (37.8°C) as combustible [44]. Combustibles are further separated into Category I Combustible (flash point below 200°F or 93.3°C) and Category II Combustible (flash point above 200°F or 93.3°C). Other countries have different definitions of flammable and combustible liquids. For example, the Commission Universitaire pour la Santé et la Sécurité au Travail Romande in Switzerland defines flammable liquids as having a flash point lower than or equal to 55°C (131°F) and combustibles as having a flash point above 55°C (131°F) [45]. They also have further subclassifications such as "easily flammable," where the flash point is below 30°C (86°F).

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Determining Physical and Spectroscopic Properties

Joaquín Isac-García , ... Henar Martínez-García , in Experimental Organic Chemistry, 2016

5.2.3 Flash point

The flash point is the lowest temperature at which a volatile substance evaporates to form an ignitable mixture with air in the presence of an igneous source and continues burning after the trigger source is removed. This parameter is related to the degree of danger of a volatile substance. Tests to determine this property often use a small flame for ignition. The liquid is heated slowly from a temperature lower that the flash point, with increasing temperature steps and applying a test flame to the vapor chamber. The flash point is the temperature at which a flash is observed when applying the flame or ignition source.

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Information on data fields

Anna Wypych , George Wypych , in Databook of Preservatives, 2015

FLASH POINT

The flash point is the lowest temperature in degrees Centigrade at which so much vapor develops under normal pressure that it results in a flammable mixture together with the air over the liquid level. Different methods are used in the test with Cleveland cup being the most suitable method for testing biocides. Cleveland open cup is used to determine flash and fire points of liquids with flash point above 79°C and below 400°C, such as biocides (ASTM D92 Test Method for Flash and Fire Points by Cleveland Open Cup). Standard gives the methods of determination using manual and automatic Cleveland open cup apparatus. About 70 ml of test liquid is heated first rapidly then slowly on approaching an expected flash point. Test flame is applied to surface to ignite vapors. Test flame is natural or bottled gas flame (full description included in the standard). Test flame is applied first when the temperature is 28°C below expected flash point and then in 2°C intervals. The flash point is the lowest temperature at which vapors are ignited by the test flame.

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Biodiesel from Plant Oils

Nikul K. Patel , Shailesh N. Shah , in Food, Energy, and Water, 2015

Flash Point

The flash point (FP) of a fuel is the temperature at which it will ignite when exposed to a flame or spark, i.e., it is the lowest temperature at which fuel emits enough vapors to ignite. The FP varies inversely with the fuel's volatility. This property is measured in accordance with ASTM (American Standard for Testing Materials) D93, which is tested by the Pensky–Martens closed-cup method. In this type, the cup is sealed with a lid through which the ignition source can be introduced. Closed-cup testers normally give lower values for the FP than open-cup testers (typically 5–10 °C lower, or 9–18 °F lower) and are better temperatures at which the vapor pressure reaches the lower flammable limit. The FP is an empirical measurement rather than a fundamental physical parameter.

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Li-Secondary Battery

Jens Tübke , ... Johanna Vogt , in Electrochemical Power Sources: Fundamentals, Systems, and Applications, 2019

12C.3.2 Critical Temperatures

Flash point is the temperature where the combustible material can ignite by an external ignition source. It is the lowest temperature at which vapors of the material will ignite, when the flammability and an ignition source are given. Ignition sources could be, for example, an external fire, sparks from inside the cell, glowing wires, or arcs from electrical connections.

The ignition energies for flammable vapors are in the region of 0.025–0.25 mJ depending on the substances. The spark energy, however, is much higher. That means that for low ignition energy of vapors there are plenty of ignition sources available. Therefore, the elimination of ignition sources is not a robust method to prevent fire [30].

The flash point for the main solvent of conventional electrolytes, the ethylene carbonate (EC) amounts to 150°C. Electrolyte additives used to reduce their viscosity and therefore leading to a higher conductivity, such as e.g., dimethyl carbonate (DMC), could be, however, ignited already at 16°C—see Table 12C.2.

The flash point temperature of solvents could be calculated via the boiling point, the evaporation enthalpy, and the lower limit of the flammability [29,31] or approximately via the boiling point and the molecule stoichiometry within ±10K [32].

Self-extinguishing time, fire point is a further parameter which is related to the flammability is the time which describes how long an ignited sample continues to burn. This depends on the ability of the fire to generate sufficient heat to evaporate enough fuel (solvent) to keep the fire burning.

Often a substance will ignite briefly, but vapor might not be produced at a rate to sustain the fire. Only at temperatures ≥ fire point the fuel will continue to burn for at least 5   seconds after external ignition. The fire point is usual about 10K higher than the flash point. There is no direct relation between flash point and self-extinguishing time. Even samples with a self-extinguishing time of zero exist [29].

Neither flash point nor fire point depend directly on the ignition source temperature, but it may be understood that ignition source temperature is considerably higher than either the flash or fire point [33].

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Lubrication

Eric Sloman , in Plant Engineer's Reference Book (Second Edition), 2002

40.4.4 Flash point

The flash point is an oil is the temperature at which it gives off, under specified conditions, sufficient vapour to form a flammable mixture with air. This is very different from the temperature of spontaneous combustion. The test is an empirical one and the result depends upon the instrument used and the prescribed conditions. For example, the flash point may be 'closed' or 'open', depending on whether the test apparatus has a lid or not. As far as lubricating oils are concerned, the test is of limited significance, although it can be indicative of contamination (for example, the dilution of crankcase oil by fuel).

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Solvent Systems

Laurence W. McKeen , in Fluorinated Coatings and Finishes Handbook, 2006

6.10 Flash Point and Autoignition

The flash point of a coating is the lowest temperature at which vapors above that liquid will burn when exposed to a source of ignition (i.e., a flame). Flash point is a direct function of the solvent system. A coating's flash point is typically that of the most volatile solvent in the solvent system. The flash point is used by regulatory agencies to specify shipping methods and containers and storage conditions and quantities. During the application of a flammable material, one must avoid many hazards that can cause fires. These details are usually described in the

MSDS. However, when the product is modified or thinned, it is possible the flash point would change. A fire and explosion issue that is less known to most coating users is autoignition or spontaneous ignition. The autoignition temperature of a coating is the lowest temperature at which a material will ignite in the presence of sufficient oxygen without an external source of ignition, such as a spark or flame.

Fortunately, most common flammable and combustible solvents have much higher autoignition temperatures than flash points. These are usually in the range of 300°C (572°F) to 550°C (1,022°F). Autoignition has its most important impact on fluoropolymer coatings in the oven. Because of the high bake temperatures used, it is possible to exceed the autoignition temperature of a coating system. If the bake oven is overloaded, solvent vapors coming off could form compositions between the Lower Explosive Limit (LEL) and the Upper Explosive Limit (UEF). If the oven operates above the autoignition temperature, then a powerful explosion could occur. Any part of the oven, such as exposed heater elements, could be above the autoignition temperature. The LEL is defined as the lowest concentration by volume of vapor in air at which the mixture will burn. The UEL is defined as the highest concentration of vapor in air at which the mixture will burn. Above the UEL there is insufficient oxygen in the mixture to support combustion. Table 6.1 shows the flammability properties of several common solvents. ^[4]

Table 6.1. Flammability Properties of Several Common Solvents

Solvent	Closed Cup Flash Point, °F (°C)	Lower Explosive Limit, % v/v	Upper Explosive Limit, % v/v	Autoignition Temperature, °F (°C)
Acetone	0 (-18)	2.6	12.8	905 (485)
MEK	19 (-7)	1.8	11.5	941 (505)
Toluene	39 (4)	1.3	7	995 (535)
Isopropanol	54 (12)	2	12	797 (425)
Xylene	77 (25)	1.1	7	977 (525)
Aliphatic Hydrocarbon (150°C–200°C boiling)	∼106 (∼41)	0.6	6.5	500 (260)
Aromatic Hydrocarbon (160°C–180°C boiling)	∼118 (∼48)	1	7.5	925 (496)

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Other Possible Examinations Conducted on Fire Debris

Eric Stauffer , ... Reta Newman , in Fire Debris Analysis, 2008

14.6.2 General Principles

Each technique presents a certain degree of variation, however there are some general principles that are equivalent for all techniques that need to be understood by the criminalist prior to performing flash point testing.

A/ Elements of a Flash Point Tester

Each flash point tester has some common elements. They all have a cup in which the liquid is placed. They also have a heater used to raise the temperature of the cup. A thermometer is present in the liquid to be tested in order to measure its exact temperature at the time of the test. An ignition source, usually a very small flame or an electrical wire that is heated, is present and can be moved into the vapor phase above the liquid at a given time. Finally, closed cup flash point testers have a lid atop the cup where the specimen is located. This lid is movable in order to create an opening for the ignition source to penetrate and enter in contact with the vapor phase.

B/ Ignition Source

As previously stated, each flash point tester has an ignition source, used to ignite the vapor phase above the liquid. Most testers use either a heated electrical wire or a small flame. For those techniques that require the use of a small flame, the size of the flame varies from 2 to 5 mm in diameter depending on the technique, and typically burns butane or propane gas.

C/ Barometric Pressure Correction

Flash point data is always provided for a nominal pressure of 101,325 Pa. Unless the ambient laboratory pressure is also 101,325 Pa, flash points need to be corrected to reflect the difference in barometric pressure. With modern automatic apparatuses, this function is often automatically incorporated. The apparatus has a built-in pressure sensor and a computer performs the calculations. With apparatuses that do not include this function, the flash point value needs to be corrected using the following formula:

$FP\text{ =}T\text{ + 0}\text{.25}\cdot \text{ (101,325 -}P\text{)}$

where

FP = Corrected flash point for standard pressure in [°C]

T = Measured flash point in [°C]

P = Ambient pressure in [°C]

D/ Manual, Semi-Automatic, and Automatic Testers

As previously stated, there are automatic, semi-automatic, and manual apparatuses. The degree of automation may vary from one manufacturer to another and from one technique to another. In general, automatic apparatuses perform all the tasks except placing the liquid in the cup. Nevertheless, there are even some manufacturers that produce autosamplers, which provide the user with a carousel carrying a dozen or more samples. The automatic apparatus controls the temperature of the sample, the ignition process, the detection of the flash, and the barometric pressure correction. A semi-automatic apparatus typically controls the temperature of the specimen, the ignition process, and the barometric pressure correction. By contrast, the flash point detection is left for the user to observe. A manual apparatus is usually very simple and the user has to control and perform all operations.

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