Tempest's Belt-Drive Power Blowers are what started it all. The first versions of the unit were designed in the late 80's to introduce Positive Pressure Attack (PPA) to the fire industry. Today, our current models boast a number of updated features and changes from the old version, but still hold true to the original idea: Keep the motor low to the ground to reduce vibration and perfect the pulley system to maximize RPM/performance. The BD's are the only units available in a 27" model. Originally designed for FDNY, the 27" Belt-Drive is the ultimate in positive pressure ventilation.