The invention relates to an apparatus comprising an injection device (1) for producing a flow of a high-speed combustible gas mixture, and a burner head (2) in which said flow is injected through a tabular extender (70) connecting said injection device (1) to said head (2). The extender has a maximal length higher than 600 mm and includes at the gravity center of the device assembly, means for suspension to a portion of the operator's body.