The reason to why they can't is based their weigh and age the average of blood in an adult is 5 liters same as a child weighing 80 kgs so i think that it would depend on your age and weight
When a fire is lit, it releases CO2 which will allow the combustion reaction to occur. When a fire is lit, energy is being emitted causing the paper to burn in contact with oxygen. The paper doesn't light up when in usual contact with oxygen because there's not energy fueling the reaction to occur.
