What is a dry riser, and how does it work?

A dry riser is a vertical steel pipe running up through a building with a breeching inlet at ground level and a landing valve on each upper floor. It sits empty. When the fire and rescue service arrives at a fire above ground level, they connect a pumping appliance to the inlet, charge the pipe, and take water off the landing valve on the floor below the fire.

That is the whole idea. It is not a system that fights a fire on its own, and nothing about it is automatic. It is plumbing that saves the brigade from running hose up eight flights of stairs while the building burns.

Why the pipe is dry

The obvious question is why it is not simply kept full. Three reasons, and they are all practical.

A charged pipe in an unheated stairwell or an external shaft freezes. It also corrodes from the inside over years of standing water, and a corroded fire main is a fire main that fails at pressure. And a leak inside a protected fire-fighting shaft does real damage to the one route people are escaping down.

Keeping it dry removes all three problems and costs about ninety seconds on the night, which is the time it takes a crew to connect and charge it. Above a certain height that trade stops being worth it, which is where wet risers come in. If you are trying to work out which one your building has, that comparison is the whole of our guide on the difference between a wet and a dry riser.

The parts, and how each one fails

The dry riser inlet, or breeching inlet

A twin or four-way inlet in a box on an external wall, usually within eighteen metres of a hard standing the brigade can park on. It has instantaneous couplings, a cap on each, and a glazed or louvred door.

What goes wrong: caps go missing, so the couplings fill with grit, silicone, cigarette ends and rainwater. Doors get painted shut or locked with a padlock nobody has the key to. The sign identifying it disappears under render. And on more than one refurbishment, the hard standing the inlet was sited for has been landscaped into a planter.

The riser pipe

Usually 100mm or 150mm galvanised steel, running vertically, normally inside a protected shaft or fire-fighting stair.

What goes wrong: less than you would think, which is exactly why it goes unlooked at. Corrosion at the joints and mechanical damage from other trades are the two real risks, and both are found by pressure testing rather than by looking at it.

The dry riser outlets, or landing valves

A gated outlet on each floor, in a cabinet, with a cap and a chain. The trade calls it a landing valve; most people searching for it call it a dry riser outlet, and they are the same thing.

What goes wrong: valves seize. A gate valve that has not been operated in four years does not open under pressure with a gloved hand at three in the morning. Cabinets get blocked by bin stores, bicycles and furniture. Caps and chains vanish. And on residential blocks, landing valve cabinets are a favourite place to store things.

The air valve

An automatic air release at the top of the riser, so the pipe fills cleanly rather than compressing a column of air.

What goes wrong: it sticks, and nobody notices until the riser is charged.

When a building needs one

In England, Approved Document B expects a fire main where the topmost storey is more than 18 metres above fire service vehicle access level, and a dry riser is acceptable where that height is up to 50 metres. Past 50 metres the pressure a pumping appliance can develop is no longer enough and the building needs a wet riser, permanently charged and pump fed.

Below 18 metres a riser is not automatically required, but it is often still fitted, and it is regularly asked for by the fire and rescue service or written into the fire strategy for a building with a difficult layout, a deep basement or a long internal travel distance. A basement car park with no natural ventilation is a common example.

The important point for anyone managing a building: if it is there, it is part of your fire safety arrangements, whether or not the height rules required it. The Regulatory Reform (Fire Safety) Order 2005 makes the responsible person accountable for keeping it working, and no inspecting officer has ever accepted “it did not have to be fitted” as a reason it was not maintained.

Riser cupboards, and whether the shaft has to be fire rated

Two questions that come up constantly, and they are really the same question asked from different ends.

The pipe itself does not need a fire rating. It is steel, it is empty, and it is not what protects anybody. What matters is the shaft or cupboard it runs in, and that does have to be fire resisting, because a dry riser is part of the fire-fighting provision and the brigade has to be able to use it while the building is on fire.

In practice that means the enclosure around the riser is constructed to the fire resistance the building’s fire strategy requires for a protected shaft, normally the same period as the stair it serves. The access doors into it are fire doors, and they carry the same rating, self-closing and properly latched. A landing valve cabinet let into a fire-rated wall has to keep that wall’s rating, which is why the cabinet is a proper fire-rated unit and not a joiner’s cupboard.

What goes wrong here is almost always the door. Riser cupboards are the most convenient storage in any building, so they fill with cleaning trolleys, cabling and Christmas decorations, and the self-closer gets wedged because somebody is going in and out. A wedged riser cupboard door is a defect on any fire risk assessment, and it is the one an inspecting officer finds first because it takes five seconds to check.

Two things worth walking round for:

• Is anything stored in the riser cupboard? Nothing should be.
• Does the door close and latch on its own, every time? If it needs a shove, it is not doing its job.

What maintaining one involves

Two intervals under BS 9990, and they are different jobs.

A visual inspection every six months covers the inlet, the cabinets, the landing valves, caps, chains, signage and access. It is the one that catches the missing cap and the painted-shut door.

A full wet pressure test every twelve months, charging the riser to 12 bar and holding it for 15 minutes, with the outlets checked and the system drained down afterwards. It is the one that catches the joint that has been quietly corroding since the building was built.

The detail of both, and what the certificate has to say, is in our guide to what BS 9990 actually requires. If you already know all that and want the work done, that is dry riser testing.

The three things worth checking today

You do not need an engineer to find the most common faults. Walk the building and look at three things.

1. Is the inlet box openable, and are both caps on? If a cap is missing, assume the coupling is full of debris.
2. Can you get to every landing valve without moving anything? A cabinet behind a stack of chairs is a failed cabinet.
3. When was the last certificate issued, and does it name BS 9990? If nobody can produce one, the honest position is that the riser’s condition is unknown, not that it is fine.

Any of the three coming back wrong is worth a phone call. None of them costs anything to check.