In general, the open flash point is 50 to 70 degrees Fahrenheit less than the fire point. The fire point of a hydrocarbon liquid is the higher temperature at which the oil vapors will continue to burn when ignited. The flash point of a liquid hydrocarbon is the temperature to which it must be heated to emit sufficient flammable vapor to flash when brought into contact with a flame. The most obvious problem is that oil-base muds will burn. Grace, in Blowout and Well Control Handbook, 2003 FIRE Only a sufficient price difference between heavy oil and light oil could justify the use of propane clarification for the vacuum residue. The valorization of vacuum residue as a component of asphalt is a good choice, because the low vacuum residue (VR) production would not allow a rapid enough return on investment of a propane or butane clarification.

The PCA contents of rerefined oils obtained by mild hydrogenation, or without any hydrogenation, are mostly in the range 0.5-2 % according to the fractions considered. With respect to PCA, the SOTULUB process, like all processes without a hydrogenation step or a specific solvent treatment, might not be satisfactory if the PCA standard of 3 wt% were lowered or if standards concerning individual PCA were more stringent. In any case, the freezing point can be easily lowered by a suitable additive. Freezing points are slightly higher than the standard values, but this is not a drawback for the Tunisian market. Noack volatility is satisfactory and compares itself with that of virgin oil. Conradson carbon of the 400 NS fraction is a little too high and this might be due to the waste oil composition as well as sulphur content that is noticeably higher than the normal values. TAN value and flash point values accord with standards. Product analyses are given in table 4.11. The standard test material for assuring quality control for a lower-temperature flash point apparatus historically has been para-xylene however, heavier normal alkane standards, n-decane, n-undecane, n-tetradecane, and n-hexadecane have also been found to be suitable and offer a wider range of test temperatures. 10 The working range for these heavier type tests is approximately 50☌ to 225☌. Smaller volumes can be used with the newer method ASTM D7094, which uses only 2 mL of oil. 9 As with the Tag method, this method uses 50–70 mL of crude oil. Heavier products, including intermediate and heavy fuel oils, can be measured by a Pensky-Martins analyzer, following ASTM D 93. With subambient cooling, using dry ice baths and/or liquid nitrogen baths, much lower flash point temperatures can be measured, but this is often not necessary for emergency response considerations. 8 The practical working range of these two methods is –10☌ to approximately 100☌. Smaller volumes, 1–2 mL, can be measured by ASTM D6450. 7 Though accurate, the Tag method uses a comparatively large volume of oil, 50 to 70 mL. Lower viscosity products, including light fuel oils and most fresh crudes, are measured by the Tag closed-cup method. The flash point of an oil product can be determined by several methods, depending on the oil product and the quantity available. Bruce Hollebone, in Oil Spill Science and Technology, 2011 4.2.4 Flash Point

Plash point