The researchers experimented with small-scale models of indoor gas leaks to see how fires start and spread. Their tests imitated leaks from gas cylinders and studied how flames ignited from an electrical spark. They discovered that flames initially spread where the gas concentration was just right, not too dense or sparse, reaching the fastest speed in well-mixed gas-air areas. The shape of the flame depends on the gas distribution. The flammable area expands gradually, reaching the height of windowsills. The most dangerous point for ignition is where the gas leak is easiest. The study also observed a transition where flames can ignite further areas, leading to widespread combustion.