- Myth of "Some Petroleum Liquids do not have Flash Point", Part 5 of X

Myth -  Some Petroleum Liquids do not have Flash Point.

Fact -  All Petroleum Products do have flash Point.  

Even Petroleum Solids have Flash Point. An ASTM D7094 standard is for  MINIFLASH flash-point is method to determine the flash point of liquids and solids according to the standard.

It has been experienced that certain liquids do not flash under standard test conditions as explained below and creates confusion in the mind of lab technicians. The responsible phenomena is known as "masking effect".

Following is reproduced from ASTM Standard D56:05,  Flash Point by Tag Closed Cup Tester

                                               X1. FLASH POINT MASKING PHENOMENON

X1.1 A condition during flash point testing can occur with certain mixtures whereby the nonflammable component of the sample tends to inert the vapor space above the liquid, thus preventing a flash. Under this condition, the flash point of the material is masked resulting in the reporting of incorrect high flash point or no flash point.

X1.2 This flash point masking phenomenon most frequently occurs with ignitable liquids that contain certain halogenated hydrocarbons such as dichloromethane (methylene chloride) and trichloroethylene.

X1.3 Under this condition, no distinct flash as defined in 3.1.1 is observed. Instead a significant enlargement of the test flame and a change in the color of the test flame from blue to yellow-orange laminar flame is observed.

X1.4 Under this condition, continued heating and testing for flash point at temperatures above ambient temperature, have resulted in significant burning of the ignitable vapor outside the test cup, often above the test flame. This can be a potential fire hazard if not recognized.

X1.5 It is recommended that if this condition is encountered during the flash point testing of these type of materials, testing should be discontinued.

X2. FLASH POINT TEST AND FLAMMABILITY OF MIXTURES

X2.1 While the flash point can be used to indicate the flammability of liquid materials for certain end uses, flash point does not represent the minimum temperature at which a material can evolve flammable vapors.

X2.2 There are instances with pure materials where the absence of a flash point does not ensure freedom from flammability. Included in this category are materials that require large diameters for flash propagation, such as trichloroethylene. This material will not propagate a flame in apparatus the size of a flash point tester, however, its vapors are flammable and will burn when ignited in apparatus of adequate size.

X2.3 When a liquid contains flammable and nonflammable components, there are cases where this liquid can evolve flammable vapors under certain conditions and yet will not exhibit a close-cup flash point. This phenomenon is noted when a nonflammable component is sufficiently volatile and present in sufficient quantity to inert the vapor space of the closed cup, thus preventing a flash. In addition, there are certain instances where an appreciable quantity of the nonflammable component will be present in the vapor, and the material will exhibit no flash point.

X2.4 Liquids containing a highly volatile nonflammable component or impurity, which exhibit no flash point because of the influence of the nonflammable material, may form flammable mixtures if totally flash vaporized in air in the proper proportions.

NOTE 7—Mixtures such as, but not limited to, those that are chlorinated or include water may cause significant differences in the results obtained by manual and automatic instruments. For these mixtures, the precision statement may not apply.

A Research paper Illuminating Flash Point: Comprehensive Prediction Models state following:

Halogen atoms such as chlorine are also found to significantly increase the flash point of compounds. A number of descriptors describing the presence of halogen atoms such as the number of CH3X, CH2RX and CH2X2 groups, where X is the halogen atom, were selected by both linear and nonlinear models. In fact the replacement of one hydrogen atom in ethane with one chlorine atom boosts the flash point by 92C from -135C for ethane to -43C for ethylchloride. The replacement of one hydrogen atom in the methyl group of methylbenzene (flash point of 4C) with chlorine or bromine atom lifts the flash point by 63C or 75C respectively. This is consistent with the knowledge that halogen substitution of hydrocarbons very significantly deceases their flammability, indeed some halogenated compounds were active components of the fire extinguishers prior to being phased out by global warming and ozone depletion concerns.

water if present in sample, it creates an environment of moisture at sufficient high temperature in cup, which prevent the hydrocarbon vapour from giving flash thus either much delayed flash point or no flash at all.

References:
ASTM D56, ASTM D93
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.513.2046

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