This paper presents a recently developed method meant to act as a tool for objectively assessing and comparing the performance of automatic fire suppression systems. This methodology specifies requirements and procedures for evaluating the efficiency and performance of automatic fire suppression systems permanently installed in the engine compartments of buses and coaches.The testing is done according to SP method 4912 and carried out in a test enclosure where the fire performance of different suppression systems can be objectively assessed in a well-defined way. The test methodology includes a battery of fire tests simulating different engine loads, air flows and fire scenarios. Every tested system is rated according to its performance. The test method also includes testing of re-ignition due to hot surface ignition of liquid fuels.