The lower and upper flammability limits (LFL and UFL) of a gas mixture are defined as the minimum and maximum fuel concentrations that will propagate a flame through a homogeneous mixture. The BakerRisk flammability apparatus is typically used to evaluate the flammability characteristics of multi-component mixtures as part of a process hazard review. Special tests often include elevated initial temperatures and pressures, and fuels that are liquids at ambient conditions.
Flammability experiments are performed in a constant volume cylindrical chamber according to ASTM E 918 (Standard Practice for Determining Limits of Flammability of Chemicals at Elevated Temperature and Pressure). The BakerRisk apparatus is capable of performing tests with initial pressures up to 200 psia and initial temperatures up to 200ºC.
Gas mixtures are prepared by measuring the component partial pressures as they are added to the vessel. Liquid components may be added using a high pressure syringe pump, where evaporation of the liquids is assured by an internal electric heater.
Ignition of the test gas mixture is attempted using a centrally-located exploding fuse wire. A positive flame propagation result is judged by an increase of at least 7% in the initial vessel pressure.