Flash point (F). DIN 51758 (August 1985) gives this definition and explanation:
"The flash point is the lowest temperature (related to a pressure of 1013.25 mbar), at which under specified conditions vapours develop from the liquid under examination in a closed cup in such a quantity as to form a vapour/air mixture which can be ignited by a spark. Along with other variables the flash point is one criterion for the inflammability of combustible liquids through spark ignition, and as such is an indicator inter alia for the inflammability and explosibility of these substances. Classification of combustible liquids in various hazard classes for transport and storage is based on the flash point." Tandem mechanical seals are the preferred choice for sealing liquids in hazard classes Al and All of the Vbf (F< 21 °C or £ 55 °C), unless other properties of the medium require a double mechanical seal.