If Mr.Steve gets over 12,000 feet off the ground he will run out of oxygen. If it is cold outside you will have to use more hot air than when it is hot. The first aircraft to be flown was a hot air balloon was in the 1700’s and  there was animals driving it the animals were a duck, sheep, and a rooster. When they landed the duck had a broken leg and they said the sheep had just had stepped on his leg. The higher  the balloon goes the hotter the air needs to be . If there are less people the more hot air needs to be in the balloon. The balloon part is called an envelope .