21.   The company is considering adding a small engine solely to heat the air, which, Vencat said, would potentially double the range.

22.   The extra days could have exhausted his supply of propane, which he needs to heat air and provide lift.

23.   The hot surfaces then heat the air, which increases demand for air conditioning and can cause smog to form.

24.   The primary way blankets keep people warm is that they keep air heated by the skin from moving away, preventing cooling by a process called convection.

25.   The sun does not heat the air directly, but first heats the ground, which transmits the warmth into the air.

26.   Then hot burners heated the air, breathing the balloons to life.

27.   This allows him to carry much more propane fuel for burners that heat air and provide supplementary lift at night, when the balloon loses buoyancy.

28.   This comes from warming that causes large wind storms that sweep dust miles into the atmosphere, absorbing sunlight and further heating the air.

29.   To compensate, propane burners are used to heat air in a compartment separate from the helium cell, providing extra lift.

30.   When a bolt suddenly heats the air around it to that amazing temperature, the air instantly expands, sending out a vibration or shock wave.