Intermediate Topic 956 of 1102 Analytical, Lab & Spectroscopy
Flash Point
The lowest temperature at which vapors of a liquid can ignite.
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In-depth explanation of Flash Point
The flash point of a flammable liquid is the lowest temperature at which it gives off enough vapour to form an ignitable mixture with air near its surface when exposed to an ignition source. It is an important fire hazard indicator, and liquids with flash points below about 23 C are classed as highly flammable in many regulations. Standard closed-cup tests give lower values than open-cup tests. Flash point is related to vapour pressure, which is why volatile liquids such as diethyl ether have very low values. It does not measure the temperature at which a liquid burns continuously, which is the fire point, a slightly higher value.
Going deeper: Flash Point
Key ideas: Classify by flash point: below 23 C highly flammable (category 2 or 1 depending on boiling point), 23 to 60 C flammable, above 60 C combustible. Compare with the lower and upper explosive limits (LEL, UEL): ethanol vapour is flammable from about 3.3 to 19 percent in air. Store in flame-proof cabinets, ground containers during transfer and keep ignition sources away from vapours that are heavier than air.
Common mistakes and connections: Students think a liquid must be boiling to ignite, but vapour above the surface burns even when it is cold. A high flash point does not mean non-hazardous, since mists and heated liquids ignite. Flash point is not autoignition temperature, which needs no spark. Mixing vapour with air outside the explosive range will not burn. Related to vapour pressure, hazard symbols and lab safety.
Visualization of Flash Point
Flash points show fire hazard: diethyl ether at minus 45 C gives off ignitable vapour even in a freezer, while kerosene needs warming to about 38 C. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Diethyl ether has a flash point of about minus 45 C, so it ignites easily at room temperature.
Frequently asked questions about Flash Point
What is Flash Point?
The lowest temperature at which vapors of a liquid can ignite.
Is Flash Point a beginner, intermediate or advanced topic?
Flash Point is a intermediate topic in Analytical, Lab & Spectroscopy. It builds on the vocabulary of beginner topics in this area.
What should I learn before Flash Point?
Study these earlier topics in Analytical, Lab & Spectroscopy first: Refractive Index, Melting Point Determination, Boiling Point Determination.
What comes after Flash Point?
The next topics in Analytical, Lab & Spectroscopy are Thermogravimetric Analysis and Differential Scanning Calorimetry.
Can I practise Flash Point with quizzes?
Yes. The interactive lesson includes a self-check question on Flash Point, and the Analytical, Lab & Spectroscopy quiz draws on every topic in this area.
Where Flash Point fits in Analytical, Lab & Spectroscopy
Flash Point is topic 80 of 99 in Analytical, Lab & Spectroscopy.