There are two main types of fire extinguishers. On the one hand you have stored-pressure extinguishers, that are permanently under pressure, and on the other hand you have fire extinguishers that are cartridge-operated, which are only put under pressure after pushing the plunger on top of the extinguisher.
A fire extinguisher under permanent pressure is immediately put under pressure at the factory. The pressure is usually between 12 and 17 bar. The extinguishing vessel contains the extinguishing agent (foam, powder, water, or a variant) at the bottom, and the rest of the vessel is filled with a propellant to achieve the required pressure. Usually that propellant is dinitrogen (N2). Because the fire extinguisher is under such pressure, the extinguishing agent will spray out as soon as you press the discharge lever.
fire extinguisher under permanent pressure
You recognise a stored-pressure extinguisher by the presence of a pressure gauge or pressure indicator (except for CO2 extinguishers: they are always under permanent pressure (of their own) and never have a pressure gauge).
A stored-pressure extinguisher pressure has a number of interesting advantages:
- Simple construction, so there are fewer parts that can wear out
- As a result, it is usually slightly cheaper to buy
- Users can do a "check" the state of their fire extinguisher themselves via the pressure gauge
However, a stored-pressure extinguisher also has a number of obvious disadvantages:
- The extinguisher is continuously under pressure, which makes it more sensitive to leakage and small cracks that cause the pressure to escape.
- Can't be opened or refilled on site, because the extinguisher is under high pressure. This can only be done in a specialised workshop.
- As a result, you can never thoroughly check the inside of the extinguisher on site.
- This means that, in practice, stored-pressure extinguishers must be replaced after 10 years. After that period, it's legally required to do a pressure test on the extinguisher, but because the extinguisher has to go back to a workshop, buying a new extinguisher is often less expensive than.
Cartridge-operated extinguishers are not put under pressure in advance. Therefore, the vessel initially only contains the fire-extinguishing agent. You can activate the cartridge-operated extinguisher by pushing the plunger on top (as with our fire extinguishers), or by pressing a built-in squeeze lever (as shown in the graph below).
cartridge operated extinguisher with squeeze lever-activation
Whatever the system of activation is, pressing it causes a sharp pin to break open the internal cartridge filled with CO2. As a result, the CO2 gas flows into the fire extinguishing tank, putting it under pressure. If you then press the squeeze tap on the extinguisher or on the hose, the extinguishing agent (powder, foam, water or a variant) will spray out forcefully.
Activation with plunger
Because the extinguisher is only put under pressure when activated, it has a number of very important advantages:
- The fire extinguisher can be opened on site by a technician, because the vessel is not under pressure
- The fire extinguisher can therefore be thoroughly checked internally
- Can be easily refilled on site
- Easier to repair: because the extinguisher can be opened, any internal defect can easily be checked and repaired
- Almost unaffected by pressure leakage, and therefore much less sensitive (e.g. during transport)
- Because the vessel is not permanently under pressure, the fire extinguisher does not need to be retested after 10 years and reaches the full legal lifespan of 20 years
Cartridge-operated fire extinguishers only have one disadvantage:
- They are slightly more expensive
Are you hesitating between a stored-pressure extinguisher or a cartridge-operated one? A cartridge-operated extinguisher is always the best long-term choice!