Dry riser are a form of internal hydrant for the firemen to use and area only required for buildings where the topmost (occupied) floor is higher than 18 metres and less than 30 metres above the fire appliance access level. Dry risers are normally dry and depend on the fire engine to pump water into the system. Dry riser system comprises a riser pipe with landing valves at each floor and to which canvas hose with nozzles ca be connected to direct the water jet at the fire. Breeching inlets into which the firemen pumps water are provided at ground level and are connected to the bottom of the dry risers.
Codes and Standards
The relevant standards for dry risers are:
- MS 1489: Part 2 – Fire extinguishing installations and equipment : Wet and dry fire fighting mains
- MS 1210 : Part 2 – Landing Valves for Dry Risers
- MS 1210 : Part 3 – Inlet Breeching for Riser Inlets
- MS 1210 : Part 4 – Boxes for Landing Valves for Dry Risers
Landing valves are provided on each floor and should comply with M.S. 1210: Part 2. They are usually located within fire access lobbies, protected staircases or other protected lobbies, and installed at not more than 0.75 metres above the floor level. To protect the landing valves, boxes may be provided and these should comply with M.S. 1210 part 4. Fire hose of not less than 38mm diameter, 30 metres in length, complete with 65mm diam. quick coupling and nozzle (suitable for a working pressure not less than 1520kPA) should be provided at each landing valve.
The fire brigade breeching inlet installed at the bottom of the riser should comply with M.S. 1210: Part 3. Where the breeching inlet is enclosed within a box, the enclosure should comply with M.S. 1210 Part 5 and labeled ‘Dry Riser Inlet’. A drain should be provided at the bottom of the riser to drain the system after use. A two way breeching inlet should be provided for a 100mm diam. dry riser while a 150mm diam. dry riser should be installed with a 4 way breeching inlet. Breeching inlets should be located no more than 18 metres from the fire appliance access road and not more than 30 metres from the nearest external hydrant outlet. (The breeching inlets shall be located at position easily accessible and visible from the fire appliance access road and shall be near to exit staircase, where possible).
The riser pipe diameter usually located within the fire access lobby or staircase should be 150mm if the highest outlet is more than 23 metres above the breeching inlet.
(MS 1489 Part 1 (1999) Clause 8.1.2 –“ Dry rising mains should have a nominal bore of 100mm where outlet is provided on each floor on each riser and where the topmost floor level is 23m or less above the fire appliance access level. If two outlets are permitted on any one riser or if the topmost floor level exceeds 23 m above the fire appliance access level, the main should have a nominal bore of 150mm. Wet rising mains should gave a nominal bore of 150mm.”
Note : MS 1489 :1999 is superseded by MS 1489 2012 – In the latest version, this clause no longer available).
Otherwise, the riser pipe can be 100mm in diameter. The riser pipe shall be of galvanised iron to B.S. 1387 (Heavy gauge) or Class C, tested to 21 bars. Horizontal runs of pipework feeding the risers should be sloped to enable proper draining after use. An air release valve should be installed at the top of the riser to relief air trapped in the system. The riser pipe should be electrically earthed or connected to the building earth to achieve equipotential.
Static Pressure Test
The system should be first flushed to clear all debris from the inside of the riser. The riser is then hydraulically tested to a pressure of 14 bars for 2 hours, measured at the breeching inlet and a check is carried out for leakage at the joints and landing valve connections.
“ The system should be completely charged with water to a pressure equal to its design operating pressure measured at the inlet for a period of at least 15 min, operating pressure only 10 bars.