In general it is recommended to fill a transformer pit with rock ballast to extinguish the fire if there is a leakage of burning transformer oil. There is a lack of technology-neutral performance requirements for the design of solutions for fire extinguishment in transformer pit fires. This hampers the introduction of alternatives to the traditional method of filling the pit with rocks. Therefore we have conducted quantitative tests where temperatures and concentrations of CO, CO2, and O2 were measured at different position in a transformer pit subjected to burning oil simulating an accidental rupture and leakage. The tests were conducted to investigate the extinguishing capacity of one specific alternative solution, i.e. a profile plank layer over the pit. Three tests were performed with 90°C and 140°C pre-heated transformer oil. In the second test, a 19 cm water bed was used to examine the impact of rain water in the pit. The result showed that the profile plank extinguished the flames in a few seconds and that the water level did not have any significant effect on the result. The measurements showed that the temperatures peaked at 600–800°C 50 cm above the profile plank in all tests but dropped to under 100°C in 14–16 s. Furthermore the O2-concentration dropped to 3–5 vol% below the plank, which contributed to the rapid extinction of the burning oil.