I will never suggest that a person refrain from messing around with something because it is dangerous. I have always held the belief that given proper respect for the lives of those around them, people should be left free to do their best, or worse as the case may be.
That being said, this article about a diver who, while filling scuba tanks, more or less burned his house down with an oxygen fire really shows us why it is important to be careful when handling high pressure oxygen.
I guess this guy was blending NITROX and the line caught fire. He wasn’t able to get the tank shut down before the whole place went up in flames. From what the article tells us, he was blending the gas himself because he didn’t hold a cert for it, and couldn’t buy it at dive shops. I guess he’d also been known to boost steel tanks up to 4500 psi with pure oxygen.
There are a lot of people out there holding this as an example of why nobody should be blending their own gas. I think this mindset is ridiculous! I frequently blend my own NITROX and TRIMIX, but I’m constantly mindful about the presence of hydrocarbons and adiabatic heating. I can’t say I would boost pure oxygen to 4500 psi, but there is absolutely no reason that divers can’t safely handle high pressure oxygen and blend their own gasses.