Flash Point of Flammable Gases, Vapors and Solvents

Flash Point of Liquids

A flammable liquid’s vapor pressure and volatility or rate of evaporation determine its ability to form an explosive mixture. These properties can be expressed by the flash point, which is the temperature to which a flammable liquid must be heated to produce a flash when a small flame is passed across the surface of the liquid. Depending on the test methods, either the open- or closed-cup flash point may be listed. The higher the flash point, the more safely the liquid can be handled. Liquids with flash points higher than 100°F are called combustible, whereas those under 100°F are described as flammable. Those with flash points less than 70°F should be regarded as highly flammable.

Table 1.0 Flammable Limits of Some Gases and Vapors

Table 2.0 . Flash Point Data for Solvents

Calculating Flash Points

*Measured by closed-cup method

Calculating Flash Points

The following formula allows for the calculation of flash points

1,000 / ( T_F undefined +  273 ) = B_o + B₁ · log₁₀ · P₂₅

T_F = Flash point

B_o 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 . It is shown in Table 2.0 .

Table 3.0 . Constants for flash point calculations . (*These values produce more accurate results and were obtaned by excluding 2,2-dimethylbutane, naphthalene, dodecane, diphenylmethane, tetradecane, nonylbenzene, and decylbenzene.)

Table 4.0 . Calculations of flash point .

K = a variant (9 for each first branch CH₃ and 21 for each second branch CH₃3 , 16 for each first branch CH and 12 for each second branch CH2)

nHr = number of hydrogen in radicals

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

Related:

• Flash Point and Fire Point of Oil
• Leidenfrost effect
• Fluids Lubrication Oil, Grease
• Synthetic Oils Review
• Naphthenic Oils Review
• Paraffinic Oils Review

References