After the rain ceases, the sanctioning body will determine if the track surface can be dried within a reasonable time frame. The track is considered "lost" if rain thoroughly wets the surface, usually characterized by a dark look to the asphalt or concrete pavement. Track crews use jet dryers, which consist of modified jet engines, mounted upside down to allow the hot exhaust to pummel the surface. The hot exhaust acts to quickly evaporate the rainwater, and allow the surface to dry considerably quicker than normal conditions. Large scale wet-vacs are also sometimes used to supplement.