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The flash point is the lowest temperature at which a liquid chemical produces combustible vapors that ignite with an ignition source. Open and closed cup experiments determine the flash point, which varies based on pressure, amount, and location of the ignition source. The fire point and self-ignition point are higher than the flash point.
The flash point of a particular chemical refers to the lowest temperature at which that chemical, in liquid form, will produce combustible vapors which will ignite on the introduction of an ignition source. This temperature can vary, for a given chemical, based on factors including pressure, the amount of the chemical, and the location of the ignition source in relation to the chemical. The flash point for a particular chemical is, therefore, somewhat unreliable and should be used as a general guideline rather than an absolute value.
There are two basic ways in which the flash point of a particular chemical can be determined: open-cup or closed-cup experiments. Both types of experiments are based on the fact that a combustible liquid, such as gasoline, releases potentially flammable vapours. As the temperature of the liquid increases, the amount of these vapors also increases. This means that at a certain temperature, the vapor concentration is high enough to become flammable. Chemicals with a fairly low flash point are referred to as flammable, while chemicals with higher flash points are usually referred to as combustible.
An open cup experiment involves a quantity of a particular chemical placed in an open container. The chemical is heated slowly and an ignition source, such as a small flame, is introduced over the chemical at various intervals. This process continues until a temperature is reached at which the vapors of the chemicals ignite, which establishes the flash point for that chemical. Once ignition has occurred, the ignition source is removed and the vapors should then stop burning; if they continue to burn without the source, however, the burning point for a chemical has been reached.
In a closed cup experiment, the process is similar but the container for the chemical is closed and the ignition source is introduced through the lid. A closed cup experiment allows you to determine the flash point of a particular chemical when that chemical is subjected to increased pressure due to a closed system. This is important in determining safe handling conditions for various chemicals stored or transported in closed containers.
When the flash point is plotted for a particular chemical, it is typically accompanied by information indicating under what conditions that point is accurate, such as pressure details and the location of the ignition source. The fire point of a chemical is usually slightly higher than that chemical’s flash point, and the self-ignition point is even higher. The self-ignition point of a chemical is the temperature at which a particular chemical or substance will ignite on its own, without an external ignition source.
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