You might be referring to a heat lance machine used for crack sealing. A hot air lance, or heat lance, combines super heated air with compressed air to clean the crack sides, remove moisture and heat crack sides to create a better surface for sealant adhesion. It makes the existing asphalt more malleable in order to bond better to the new mix.
The chance of a good bond can be diminished by cold temperatures, dirt, and moisture. Studies have shown that heat lancing the cracks before they are sealed improves the effectiveness of the bonding. Heat lances may or may not have a flame, depending on the manufacturer.
