On a balloon equipped with a blast valve, what is the primary use of the blast valve?

• A. Altitude control
• B. Emergency venting only
• C. Temperature control
• D. Ground speed control

Answer: (A)

The blast valve is used to change altitude quickly by rapidly venting hot air from the envelope. When you open it, hot air bursts out, reducing buoyancy and allowing a rapid descent or a faster adjustment of the flight level. Heating with the burner controls ascent, while the blast valve provides a swift way to shed buoyancy when you need to drop altitude or make a precise altitude change. It isn’t intended as a temperature-control device, since venting hot air mainly changes weight and buoyancy, not the overall temperature you’re maintaining. Ground speed is governed by the wind, not by the blast valve.