Abstract: Apparatus for automatically monitoring the flash point of a liquid passing through a conduit which includes a closed equilibrator vessel into which a sample stream of the liquid is confined and volatile vapors therefrom are allowed to saturate air introduced into the vessel, and a combustible gas sensor for measuring the percent lower flammable limit of the resulting gas mixture. The system further includes suitable computing means for automatically calculating the Tag closed cup flash point of the sample liquid based on the temperature of the liquid and on the measured percent lower flammable limit, and controlling the operation of the apparatus. A method of determining the flash point of such a liquid is also disclosed.