This paper presents the main results of six large scale fixed fire fighting system tests that were carried out in the Runehamar tunnel in September 2013. It describes the background and the performance of the system. The main fire load consisted of 420 standardized wood pallets and a target consisting of a pile of 21 wood pallets placed 5 m from the rear end of the main fire load. The purpose was to investigate possible fire spread. The water spray system is a deluge zone system delivering 10 mm/min in the activated zone. The detection system was simulated with use of thermocouple in the tunnel ceiling. The alarm was registered when the ceiling gas temperature was 141°C. After alarm was obtained the system was activated manually after a given delay time that was varied in the tests. The heat release rates in tests with fire suppression were reduced to 20–45 MW compared to 100 MW estimated for a free-burn test or 75 MW in test 6 with a failure of activation. Fire spread to the target was prevented after fire suppression.