Is there a relationship between flash point and boiling range?

It is related. The following is excerpted from PRO II regarding flash point calculation. The flash point is a test designed to determine the temperature at which the vapor above an oil will momentarily “flash” or explode. There are three common tests: the open cup (D92) method, the Pensky-Martens (D93) method, and the Tag (D56) closed-container method for lighter oils. The oil is heated at a constant rate, and a test flame is periodically introduced into the vapor; the flash point is the temperature at which the oil vapor “flashes”. The results vary to some extent depending on the testing method. The following methods are available for calculating the flash point in PRO/II: Nelson – This method was developed by W. L. Nelson, and it calculates the flash point using the equation: Flash Point, degrees F = 0.64*T – 100, where T is the average ASTM temperature of the 0 to 10 percent distilled portion of the oil, in degrees F. This method is not accurate enough to distinguish between the results obtained from different laboratory tests. API – This method utilizes API Procedure 2B7.1, which relates the flash point to the values determined by the D86 test for the 10 percent distilled portion of the oil. The flash point values obtained using this method correspond to those obtained through the Pensky-Martens test procedure.

It should be fine; the boiling range reflects the purity of the material, while the flash point is primarily an inherent property of the substance

Flash point: The lowest temperature at which the vapor generated from the surface of a flammable liquid or solid ignites under the action of a test flame, in a stable air environment； The flash point is the lowest temperature at which a flammable liquid or solid can release enough vapor to form a flammable mixture with air at the surface of the liquid or solid within its container. Boiling range: When a petroleum product is heated under specified conditions in an Enneberg distillation apparatus, the temperature of the gas phase at which the first drop of condensate appears is called the initial boiling point. The highest temperature of the gas phase that can be reached at the end of the distillation process is called the final boiling point or dry point. The temperature range from the initial boiling point to the dry point is known as the boiling range. Based on the definitions of the two above, there is no connection between them.

It is related; please refer to the following article: Several Common Concepts in Combustion 1. Flash ignition: The combustion phenomenon in which sufficient flammable vapor is generated on the surface of a liquid (solid), resulting in a flame that appears briefly before going out is called flash ignition. 2. Smoldering: The slow burning process without a flame is called smoldering. 3. Deflagration: An explosion that propagates at subsonic speeds is called deflagration. 4. Spontaneous combustion: The phenomenon in which a combustible material burns on its own, without the presence of an external heat source such as an open flame, due to heating or internal heat generation and heat accumulation, is known as spontaneous combustion. In other words, it is the phenomenon in which a substance generates heat due to biological, physical, and chemical processes occurring within it, without any external ignition source; this heat causes the temperature to rise, leading to the substance catching fire on its own. 5. Flash point: The lowest temperature at which a flash fire can occur on the surface of a liquid (solid) under specified test conditions is called the flash point. In homologs, isomers have lower flash points than the nomenclature forms ； The flash point of homologs increases as their molecular weight increases, and it also rises as their boiling point increases. For mixtures of various components, such as gasoline and kerosene, their flash point increases as the boiling range increases ； A mixture of liquids with low flash points and liquids with high flash points, whose flash point is lower than the average of the flash points of these two types of liquids. The flash point of wood is around 260 degrees Celsius. The significance of the flash point: (1) The flash point is an important basis for classifying the fire hazard in production facilities ； (2) The flash point is the basis for classifying the fire hazard in warehouses storing goods ； (3) The flash point is the basis for classifying hazardous liquids into categories A, B, and C ； (4) The fire resistance rating, number of floors, floor area, safety evacuation measures, fire separation distances, and explosion-proof facilities for factories and warehouses are specified based on the classification of liquids into categories A, B, and C ； (5) Based on the classification of liquids into Category A, B, and C, regulations are established for the layout of liquid storage tanks and storage yards, fire separation distances, fire separation distances for storage tanks of flammable and oxidizing gases, as well as the layout and fire separation distances for liquefied petroleum gas tanks. 6. Ignition point: It refers to the lowest temperature at which a liquid or solid can sustain combustion under specified test conditions; this temperature is known as the ignition point. The ignition point of all liquids is higher than their flash point. 7. Autoignition point: It refers to the lowest temperature at which a combustible material can ignite spontaneously under specified conditions; this temperature is known as the material’s autoignition point. The main ways in which combustible materials catch fire spontaneously are: (1) heat generation through oxidation ； (2) Dissociation heat ； (3) Polymerization exotherm ； (4) Adsorption exotherm ； (5) Heat release during fermentation ； (6) Reaction of the active substance with water ； (7) Mixing of combustibles with strong oxidizers. Main factors affecting the autoignition temperature of liquid and gaseous combustibles: Pressure: The higher the pressure, the lower the autoignition temperature ； Oxygen concentration: The higher the oxygen concentration in the mixture, the lower the auto-ignition point ； Catalysis: Active catalysts can lower the autoignition point, while inert catalysts can raise it ； Material and inner diameter of the container: Different materials for the container walls have different catalytic effects ； The smaller the container diameter, the higher the auto-ignition point. Main factors affecting the autoignition temperature of solid combustibles: Heating and melting: After melting, it can behave like a liquid or a gas ； Amount of volatiles: The more combustible substances that evaporate, the lower its auto-ignition point ； Particle size of solids: The finer the solid particles, the greater their specific surface area, and the lower their auto-ignition temperature ； Heating time: When combustible solids are exposed to heat for an extended period, their autoignition temperature decreases. 8. Oxygen index: It refers to the minimum oxygen content required for a solid material to maintain steady combustion in a mixture of oxygen and nitrogen gases under specified conditions. A high oxygen index indicates that the material is difficult to burn, while a low oxygen index suggests that the material is easy to burn. Generally, materials with an oxygen index of less than 22 are considered flammable, those with an oxygen index between 22 and 27 are classified as combustible, and those with an oxygen index greater than 27 are considered difficult to burn. 9. Characteristics of the combustion of flammable liquids: The combustion of flammable liquids is actually the combustion of their volatile vapors; therefore, whether a liquid can burn and the speed at which it burns depend on properties such as its vapor pressure, flash point, boiling point, and evaporation rate. Three special phenomena tend to occur in fires involving open storage tanks of different types of oils: boiling over, splashing, and bubbling. Boiling over phenomenon: During the burning process, as heat is continuously transferred into the liquid layer, heavy oils and crude oils that contain water, have high viscosity, and a boiling point above 100°C will experience boiling over and splashing, leading to large-scale fires. This phenomenon is known as boiling over. Oils that can cause bumping are known as boiling-over oils. The classification and grading of liquid fire hazards are based on their flash point; they are divided into Category A (highly flammable liquids): liquids with a flash point below 28 degrees Celsius ； Category B (flammable liquids, class 2): flash point greater than or equal to 28 degrees Celsius and less than 60 degrees Celsius ； Category C (flammable liquids): three types with a liquid flash point of 60 degrees Celsius or higher. 10. Characteristics of solid combustion: Solid combustibles must undergo heating, evaporation, and thermal decomposition; only when the concentration of flammable gases above the solid reaches the ignition limit can continuous combustion occur. Combustion methods are divided into four types: evaporation combustion, decomposition combustion, surface combustion, and smoldering. Smoldering: Some solid combustibles will smolder in conditions of poor air circulation, low heating temperatures, or high moisture levels, such as bales of cotton, linen, and paper, as well as large piles of coal, grass, and wet wood.

Of course it matters. There is a certain relationship between the flash point of hydrocarbon compounds and other physical properties; for pure hydrocarbons, there is an approximately linear relationship between the flash point and the boiling point. For hydrocarbon mixture oils such as gasoline, kerosene, or diesel, the flash point is closely related to their distillation composition; the higher the boiling range of the oil, the higher its flash point.

The formula for PRO II that you provided should refer to the open-cup flash point; I’m not sure if my understanding is correct

Of course there is a connection; as the boiling range changes with rising temperature, the fractions also change. So how could changes in the properties of the oil not affect its flash point?

The formula for PRO II that you provided should refer to the open-cup flash point; I’m not sure if my understanding is correct What was said upstairs is incorrect; the flash point here should be the closed-cup flash point