Extinguishers go where somebody leaving a fire would pass them, not where there happened to be a spare bit of wall. That means on escape routes, near exits, and near the specific hazards that need a specific agent. Everything else about siting, height, brackets and signs follows from making them findable by somebody who is frightened.
On the route out
The general rule is that extinguishers sit on escape routes, near storey exits and final exits, so that somebody who has decided to leave passes one on the way and can choose to use it without going deeper into the building. Specialist extinguishers sit near the hazard instead: wet chemical by the fryer, carbon dioxide by the electrical intake, because those answer one risk rather than a general one.
Height, mounting and fire extinguisher brackets
Extinguishers are mounted so the handle is at a height an adult can lift from without stooping or reaching, with heavier units lower than light ones. A bracket on the wall is preferred to a floor stand because a stand gets moved, gets things stacked on it and gets used to prop doors. Where the wall cannot take a bracket, a properly weighted stand in a fixed position is the fallback rather than the default.
Extinguisher signs and visibility
A sign is required so that equipment can be found. In a large or cluttered space that means a sign mounted high enough to be seen over racking and furniture, not only a label at the bracket. In a corridor a wall sign at eye level is fine. The test is simple: stand where a person would be when they decide they need one, and see whether you can tell where to go.
Fire extinguisher boxes, cabinets and trolleys
Outdoor extinguishers need a cabinet or box to keep weather and interference off them, and the cabinet must not need a key that nobody has. Trolley mounted extinguishers exist for large risks such as fuel storage where a portable unit is too small to matter, and they are positioned with a clear run to the hazard. Both are specialist answers and neither replaces extinguishers on the escape route.
Other questions people ask
How high should a fire extinguisher be mounted?
So the handle can be lifted without stooping or reaching, with heavier units mounted lower. Consistency across a building matters as much as the exact figure, so people find them by habit.
Are floor stands acceptable?
They are a fallback where a bracket cannot be fixed. Stands get moved, loaded and used to prop doors, so a wall bracket in a fixed, signed position is preferred wherever possible.
Do outdoor extinguishers need a cabinet?
Yes, to keep weather and interference off them. The cabinet must not be locked in a way that delays somebody who needs it, which usually means a break glass or a latch rather than a key.
Is a fire extinguisher trolley unit ever the right answer?
On a large open risk where a portable will not do the job: a yard, a plant area, a fuel store. It is heavier and needs a clear route to move it, so its position is chosen for where it can actually be taken rather than where there is space.
When are fire extinguisher cabinets worth having?
Outdoors, in a dirty or wet environment, and anywhere units are being moved or taken. They protect the unit and mark its position, and they must not be locked in a way that delays somebody reaching for it.