Also it only takes 10-30 seconds to discharge a 30lb fire extinguisher[1] with no pause. This is not a marathon.

[1] scroll down to table in https://blog.qrfs.com/66-ultimate-guide-to-fire-extinguisher...

12kg is like a two year old child or a small-to-medium sized dog.

Yes.

12kg shouldn't be much of a problem for most people, if the weight comes in the shape of a dumbbell and stuff ain't on fire.

But wielding a toddler-sized implement awkwardly in front of a fire while you are a bit panicking yourself, might be a struggle for many people.

Especially since you probably never practiced this, and you might even have to hold the thing one-handed, so you can aim with the other hand

When you get to 12kg it usually mean a cylinder and a hose. You have the cylinder with handle in one hand and the hose in other.

Fire extinguishers are easier to carry than a dumbbell. They're a tall cylinder with a handle at the top.