Thanks for answering, I don't want to affront you, I would just like to know the origin of your knowledge, are you guessing or have you already followed unsuccessful cases of CTB with party helium?
Party helium is never 100% helium, you don't need anyone to confirm this, you can check the specification when you order. Helium is expensive to produce and does not need to be 100% for balloons. Also as said, air is mixed with it to prevent "accidents".
You can buy 100% helium for welding but most people who decide against gas are concerned about the overall cost of the setup and storage issues. You can use other gasses as mentioned but
@wagner2029 does not have to justify his information, if you search the forums you will see that the same question has been answered many times.