A riser is plumbing for the fire service. It is a pipe running up a building with outlets on each floor, so a crew does not have to run hose up the stairs from a pump in the street. A dry riser is empty until the fire service charges it through an inlet at ground level. A wet riser is permanently full and pressurised, which is what taller buildings need because a pump on the street cannot reach the top.
When a building needs one
The trigger is height, and the requirement comes through Building Regulations approved document B rather than through the Fire Safety Order. Dry risers appear in buildings above the height at which firefighting from ground level stops being practical, and wet risers take over higher still, where the pressure a pumping appliance can deliver runs out. Once fitted, the Order's article 17 maintenance duty keeps them working.
What testing involves
A visual inspection of the inlet cabinet, the outlets, the valves and the padlocks or seals at intervals through the year, and an annual pressure test of the installation to the recognised standard, which pressurises the main and checks for leakage and for valve performance. The annual test is a wet job in a dry building, which is why it is scheduled rather than fitted around.
What goes wrong with them
The inlet box is the part in the street, so it is the part that gets damaged, blocked, painted over, parked in front of or stolen for its brass. Outlet valves seize. Padlocks are replaced with the wrong ones so the fire service key does not fit. Landing valves leak. None of that is visible from inside the building, which is the argument for the visual inspections between annual tests.
Hose reels and hydrants, which are different things
A fire hose reel is a fixed first aid firefighting appliance for occupants, fed from the building's water supply, and where one is provided it is maintained and tested like any other equipment. A fire hydrant is the fire service's water source in the street or on the site, and a private hydrant on a large site is the owner's to maintain and to keep accessible and marked.
Questions people ask about dry riser
What is a dry riser?
A vertical pipe with outlets on each floor, kept empty and charged by the fire service through an inlet at ground level, so crews do not have to run hose up the stairs.
What is the difference between a dry riser and a wet riser?
A dry riser is empty until the fire service charges it. A wet riser is permanently charged and pressurised by the building's own pumps, which is what taller buildings need.
How often should a dry riser be tested?
Visual inspections through the year and an annual pressure test of the installation to the recognised standard, with the results recorded.
Who maintains a private fire hydrant?
The owner or occupier of the site it serves, who must keep it accessible, marked and working, because it is the fire service's water source for that site.