Flash Point and Firepoint – how safety is maintained with analysis.

Flash point (open (100ml) and closed (100ml)) and firepoint. Flashpoint and fire-point are important tests when determining safety of certain systems. It may come as a surprise that no liquid burns and it is in fact the vapours just above the liquid that actually burn. Hence performing a closed cup flashpoint (i.e. with a lid on the container the flashpoint is lower because the vapours are allowed to collect. Closed flashpoints are usually most important in systems where the vessel is closed such as fuel tanks and when transporting fluids. Open cup flashpoints are usually slightly higher because there is no lid to the container and the gases can escape, hence a higher temperature is needed for sufficient vapour to collect above the fluid to cause a flash. A flash is when a flame is placed just above the liquid the vapours ignite and then go out quickly in a ‘flash’. If you continue heating the fluid past the open flash point, to a point at which the vapour ignites and stays lit because the fluid is at sufficiently high a temperature for more vapours to be produced to fuel the flame, then this is termed the fire point.

Tested On: Any product that has a Material Safety Data Sheet. Nearly every product has this as a new oil batch test and these are important safety tests. However, in condition monitoring it is mostly used in engines to detect fuel dilution, petroleum product drilling/mining equipment and seal oils to detect contaminating petroleum products such as natural gas, and in heat transfer / metal quenching systems to determine if product is safe for continued use.

Diagnostic significance & Typical Diagnostic limit: The limits used are often application specific and involve analysing the trends. However, diesel fuels closed flashpoints need to be over 56OC, whilst lubricating oils need to be over 200OC. In heat transfer systems the comparison of the gap between the open and closed flashpoint is important as it determines when the oil has degraded to a point in which small light end fractions of the oil have collected as a vapour in the system and run a significant fire risk.

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