Flash point

Flash - instantaneous combustion of a mixture of air and fumes of combustible substances, accompanied by a bright brief glow. There is no stable combustion. The flash point is the minimum temperature of the condensed matter, at which vapor is generated above their surface, which flash when a spark, flame, or hot body appears.

The ability to flare at relatively low temperatures has fluids that belong to the category of flammable. The maximum flash point of such substances in closed crucibles is + 61 ° C, in open - + 66 ° C. Some substances are capable of spontaneous combustion, having reached the characteristic temperature of ignition for them.

The determination of saturated vapor pressure is possible for any combustible liquid. It increases in proportion to the increase in the temperature of the substance. As soon as the flash point reaches the critical (maximum) index, it becomes possible to maintain combustion.

However, the onset of a vapor-liquid equilibrium will take some time, which is proportional to the rate of vapor generation. Steady combustion can be achieved by achieving a certain (for each substance of an individual) ignition temperature, since the combustion temperature is always higher than the flash point.

Direct changes in the temperature at which substances break out have certain difficulties. Therefore, the temperature of the flare is considered to be the temperature of the walls of the reaction vessels in which this outburst is observed. The temperature depends directly on the conditions of the occurring heat exchange inside the vessel itself, on its catalytic activity, on the environment, on the volume of the liquid in the vessel.

Indicators of experiments allow us to calculate the temperature of combustible substances permissible for transportation and storage. The flash point in closed crucibles is measured, as a rule, according to Pensky-Martens. In open crucibles it is refined experimentally.

Especially dangerous are liquids that can flare at temperatures below -18 ° C in closed crucibles, below -13 ° C in open ones. Constantly dangerous are considered liquids, the flash of which is possible at a temperature of + 23 ° C in closed crucibles and up to + 27 ° C in open. Temperature indicators for hazardous liquids are up to + 60 ° C inclusive with closed crucibles, up to + 66 ° C inclusive - when open.

The difference in flash, ignition and combustion temperature varies considerably, and it is individual for each substance. The flash point of diesel fuel, for example, is not more than 70 ° C. The temperature of its combustion is + 1100 ° С. The ignition temperature ranges from + 100 ° C to + 119 ° C. But the flash point of gasoline, due to very high volatility, is + 40 ° C, and sometimes less. Its ignition temperature is + 300 ° C. The indicators concerning gasoline are somewhat generalized. They need to be considered average, since there are different types of gasoline (automobile (summer, winter), aviation) with significantly different characteristics and, correspondingly, different temperatures of flare, ignition, combustion.

Combustion is a process accompanied by the release of a large amount of heat with a characteristic emission of light (glow), which is possible when a temperature is reached for a particular substance and access to oxygen or other substances (sulfur, bromine vapor, etc.).

The most dangerous are explosions, characterized by an instant chemical reaction with the release of huge energy and carrying a mechanical work. Fire in the explosion can spread to 3000 meters in one second. Combustion of a mixture at this rate is called detonation. The shock waves that are the result of detonation often become the cause of significant destruction and accidents.