The styophome (sp) cheap ones are the best....BESURE TO LEAVE A SMALL HOLE IN THEM .
It still get back to safety for you first and the plants next.
Dry Ice and paint ball tanks are only for rich growers.
Nothing beats $20 bucks for a 2.5 MONTHS supply in a large room.
Remember Einstein could not change a light bulb.
Also he and Edison worked at the patent office. Does that tell you something, think real hard PATENT OFFICE