Carbon dioxide extinguishers are commonly supplied in two sizes for general use. The larger one holds roughly twice the agent of the smaller and runs for longer with more reach, and it weighs enough that some of the people expected to use it will struggle. Choosing between them is a judgement about the room and the people in it, not a default.
What the extra agent buys
A longer discharge and a longer effective throw. On a class B fire that matters, because the blanket of gas has to be maintained over the surface while the vapour above it is displaced. On a small equipment fire it matters much less, because the fire is over in the first seconds or it is not going out at all.
The weight problem
Carbon dioxide cylinders are heavy for their capacity because the vessel has to hold a high pressure. The larger size is a two handed lift for many people and a genuine obstacle for some. Where the room is served by staff who will not be able to lift and aim it, the smaller unit that gets used beats the larger one that does not.
Rooms that justify the larger size
Plant rooms, switch rooms with substantial equipment, laboratories with solvent quantities, and areas where a class B risk is more than incidental. These are places where the fire, if it happens, will not be a single failing appliance.
Rooms that do not
A server cupboard, a comms rack, a small office with a few pieces of equipment. The smaller unit is easier to site, easier to handle and is enough for what is credibly going to burn. Over sizing the provision here buys weight rather than capability.
Questions people ask about co2 fire extinguisher 5kg
Is a larger carbon dioxide unit rated for more classes?
No. The class ratings are the same; what changes is the size of test fire within those classes that the unit extinguished, and the run time.
Does the larger size need a different service?
The same regime applies: weighed at the annual service and pressure tested at the longer interval. The cost differs slightly and the schedule does not.
Can a trolley unit be used instead?
Wheeled carbon dioxide units exist for large risks and remove the lifting problem entirely. They need floor space and a clear route, which is why they are a plant room answer rather than a corridor one.