Mostly because it's pointless. The bottle can only be filled up with specialized equipment, and they have a gauge to tell them how much is in it. Once the extinguisher is used, it has to be returned anyway to be refilled regardless how much CO2 you may have used. If you happen to be using it when it runs out, well, the fire is out of control already.
Class A
The gas used in fire extinguishers is carbon dioxide. That is only for a CO2 extinguishers High pressure and no Gauge on the unit(about 2000psi). Normal Dry chemical extinguisher ABC, BC (195psi)Use Nitrogen as the propellent.
Fire extinguishers commonly contain water under pressure, compressed carbon dioxide, foam, or specialized dry chemicals, depending on the type of fire they are designed to put out.
Class A
There are two main types of fire extinguishers: stored pressure and cartridge-operated. In stored pressure units, the expellant is stored in the same chamber as the firefighting agent itself. Depending on the agent used, different propellants are used. With dry chemical extinguishers, nitrogen is typically used; water and foam extinguishers typically use air. Stored pressure fire extinguishers are the most common type
Many pressurized water fire extinguishers are charged with air at 100 psi.
Class A
USFA fire extinguishers is a good brand. Remove the safety pin if there is one and break the safety seal. After that exert pressure by squeezing the handle.
Nitrogen can be used in fire extinguishers as gas propellant.
When it comes to fire extinguishes, the smaller the volume of the extinguisher the more pressure the gas has. So if the size of the fire extinguisher is small, the pressure might be high.
FIRE extinguishers are used to put out fire.
You can get fire extinguishers recharged at fire equipment companies, some hardware stores, and fire departments.