That’s a fair question Well first of all it is mostly hazardous to the outrageous profits of the gas companies
But in proper response to the intent of the questions – it can be very hazardous - but only if one does! There is hydrogen involved in this, any system is using hydrogen as fuel can be a liability, hydrogen same as plastic bags is not a toy! I've known folks that were trying to ignite the hydrogen for kicks...that is the kind of dumb thing I am talking about!!! They simply wanted to see if it would explode... Naturally it will, duh! Hydrogen ignites if you apply a match to it, and then its flame runs at 3.5 Mach! That’s gonna win a race no matter how fast you run.
Throughout the books at Water4Gas Ozzie the author of the Water4Gas information has inserted more than enough precaution notes, for every area that may harm you or damage the vehicle. Even down to the details of toxic glues, he placed Big Bold warnings that you can’t miss unless you really do have blinders on
With all of the above in mind, Hydrogen-On-Demand as laid out at W4G is NOT more harmful than the usual vehicular technologies which involve gasses, cooling, etc. For example we all know that the radiator is there to perform a key function of cooling down the engine, and if it is not there and functioning well the automobile will go up in smoke. But if you open the radiator cap when it’s heated, you're going to get hurt, ya? The hazard is because of the existence of the radiator, the hazard is in neglect and carelessness of safey rules. There are safety rules and they are essentially simple, but you need to be aware of them and apply them.
If you heed the rules AS OZZIE HAS WRITTEN THEM FOR US, you should not be in any harm’s way. Ozzie does demonstrations of his system to folks almost daily and it is totally safe because he adheres to his own rules. Ozzie never had a fire, explosion or meltdown. Follow his footsteps for maximum safety!
Let me give you a real example: in the installation chapter you will see a warning that you HAVE TO use an output hose that is at least 4 feet long, to safeguard against fire hazard. Don't cut it short even if the device is closer than 4 ft. Every similar caution is highlighted in the book so they cannot be missed.
Bottom line: Hydrogen-On-Demand indicates that we are not storing Hydrogen! In routine operation we're consuming any hydrogen that we produce instantly. There is no Hydrogen storage tank to explode in case of an accident. That makes ours the safest system out there.
What about the glass jar? Is that dangerous? ?
No danger that I know of. I have yet to see Even one of the glass jars crack or break. One day recently I was cleaning my 6 jars which were in the Toyota. All six jars were already cleaned and therefore were almost invisible, and were lined up at the curb. My neighbor didn'tnotice them and moved her car back right directly over them. They were flipped to the road which caused a great deal of noise. I thought to myself: "Now THIS is damage!"

But when I inspected the jars from under her wheels, none of them was cracked, chipped or damaged in any way! Not a scratch!

Still if you do have a concern, a VERY durable plastic substitute is ok. Not a cookie jar or any other food container – cheap plastic containers are not an option because they can melt in less than 10 minutes of operation.