Fire Resistant Staircases (Q+A) G#20881

By March 15, 2019 August 2nd, 2019 Code, Encyclopaedia, Q&A
MCM Havas Accommodation Stairs

Fire Resistant Staircases Q+A

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Fire Resistant Staircases Q+A
About:


I am a year 2 Interior Architecture and Design student.

I have a question related to my design studio and advance technology project.


Q1. Is it possible to have staircase that is visually exposed with fire rated quality?

For instance, having fire rated glass partition and fire rated glass door in the middle of the building.


S1. The following answers are a generalization and the Building Regulations and the Building Control Officer should be consulted to the actual requirements of your proposals, other legislation may apply.


A1. Internal Means of Escape Stairs and safe corridors

  • Means of Escape stairs are usually in a separate fire compartment all on their own
  • Usually contained within the core of buildings along with lifts and service risers
    • ‘Core’ does not have to mean ‘in the middle’ cores can be at the perimeter
  • Means of escape stairs are calculated collectively to enable the escape of all of the people from the building
    • Canary Wharf towers contain 10,000 people where phased evacuation is used to avoid congestion on stairs
  • Means of escape stairs discharge to a place of safety
    • e.g. public street, not to a back garden or alleyway
    • and not into the ground floor of the building (escapees would still need to find their way to an external door in potentially smokey conditions)
  • If the means of escape stairs is in the middle of the building if will need a safe corridor from the stairs to an external door leading to an external place of safety
    • This safe corridor is probably at ground level, but may also be on other adjacent floors: basement, lower ground floor or ‘piano nobile’ upper ground floor where access to the street or ground is practical and direct
  • The safe corridor will need to be of the same fire performance as the stair enclosure
    • It may have doors into it, of the same fire performance, but doors must not open into the flow of escapees
      • Corridors will need to be wider if doors do open into the flow of escapees
      • Crowd control barriers will need to guide escapees away from any inward opening doors
    • Any doors in the escape corridors walls, enabling crossing of the escape corridor, must be on hold-open devices (see below) that fail safe closed and close when fire alarms are activated
    • Final escape doors must open outwards in the direction of flow of escapees
  • Fire and smoke resistant doors provide access to and from the staircase enclosure and limit the amount of smoke entering the stair enclosure
    • Fire doors including ironmongery need to be competent and maintained (working properly)
    • Fire doors should never be jammed open (often by a fire extinguisher)
    • Fire doors can be on door closers with electro-magnetic hold-open ironmongery that release the doors to close, on electrical failure (fail safe) or in an emergency triggered by the fire detection and alarm system
    • Egress doors at ground level should never be chained and padlocked but should have competent ironmongery
    • Staircases and escape routes should never be used for storage of goods or packaging
  • Some buildings have air pressurised staircase compartments to ensure smoke cannot enter the stairway
    • This pressurisation need only occur during a fire rather than 24/7
  • Their primary purpose is means of escape and secondary purpose passage between floors in daily use
  • Walls are usually but not exclusively close fitting to the stairs
  • Materials in these staircases are ideally non-combustible and not generate smoke or flaming droplets
  • Surface materials in a means of escape route including stairs must be low surface spread of flame
    • BS 476:Part 7 Class 1 or Building Regulations Class O
    • Masonry; brick, stone, block, concrete, plaster/render, plasterboard, gypsum, cement, lime
    • Other materials will need properties checking
    • Manufacturers of products usually have had their materials tested and have test reports and literature revealing their properties and suitability for applications
  • Gas pipes should not be run within these compartments
  • Emergency lighting is an essential service but not 24 hours a day only during a fire or if the stairs are in use
    • PIR detection of people can turn the lights on if people are present
    • Windows can provide daylight to stairs supplemented by artificial lighting after dark
    • Stair lighting does not need to be on 24/7 if people are not present on the stairs

A2. External Means of Escape Stairs

  • A means of escape stairs can be outside the external envelope of a building
  • A fire resistant enclosure or compartment is no longer needed
  • The stairs must be protected to prevent flanking fire coming from any adjacent glazing from reaching the staircase and users.
  • The stairs do not need to be within a weather-tight enclosure
    • but do need to be durable, grippy handrails and non-slip treads and landings in external conditions
  • Emergency lighting will need to be provided but not 24 hours a day only during a fire or if the stairs are in use
    • PIR detection of people can turn the lights on if people are present
    • Windows can provide daylight to stairs supplemented by artificial lighting after dark
    • Stair lighting does not need to be on 24/7 if people are not present on the stairs
  • See A8 Glazed enclosure to fire escape stairs

A3. Accommodation Stairs

  • Accommodation stairs are usually in an entrance foyer or atrium, not in a separate fire compartment
    • But Havas, Kings Cross, London (see illustration) has 2 large stairwells linking all floors where accommodation stairs are used
      • in their own fire compartment separated from adjacent office accommodation floors
      • fire resistant glazed screens and doors separate the stairwell from accommodation
      • these stairwell also contains kitchenette (a potential source of fire) and meeting spaces
      • the flights are dog-leg,
      • Each flight springs from and lands to 4 sides of the open stair well adding consistency with variety at each floor
  • Usually highly visible to encourage stair use in preference to lifts to keep people active and fit
    • Offer inter-visibility between floors and greater potential for staff interactions
  • They are not normally included in the calculations for means of escape capacities
  • There is no need for fire and smoke doors to access it, except if like Havas
  • Their primary purpose is passage between floors in daily use and they are discouraged as a means of escape because they are not protected from smoke or fire
  • They are not usually enclosed but highly visible
  • Materials in any staircases are ideally non combustible and not generate smoke or flaming droplets
  • Emergency lighting is a non-essential service in day light filled and artificially lit atrium
  • Accommodation stairs are often illuminated for visual effect, consuming energy and potentially generating carbon 24/7, Photovoltaic (PV) power from the roof or façade could be used to power this non-essential service

A4. Temporary fire resistant enclosure to accommodation

  • Regulations are legal minimum, (in the case of staircases, to enable escape in the event of a fire and to prevent loss of life); but are not the only reason for applying them where there is no legal or regulatory requirement.
  • For reasons of insurance or protection of property, accommodation and possessions the client may require a staircase to be open plan generally but closed off in the event of a fire, to prevent fire passage between accommodation floors
  • In this case the stair follows the accommodation stair rules A3 above
  • And a retractable and deployable fire curtain can be installed around the staircase at ceiling level(s)
  • In the event of a fire being detected the fire control systems will initiate the deployment of the curtain, it will concertina down from the ceiling and make a fire and smoke tight seal at the floor, perimeter walls and all changes of direction around the stairs.
  • The ‘Fail-safe principle’ requires that in the event of electrical failure the curtain will deploy down.
  • The curtain is fire resistant and the whole is designed and tested to levels of performance, e.g. 30/60/90/120 minutes for integrity and if required insulation too, some require sprinklers at the curtain side, to achieve insulation
  • In the event of a fire the stair becomes inaccessible, you cannot get in or out, without destroying the curtain’s integrity
  • The curtain is opaque, so the staircase position is not obvious to visitors, staff will know, if they are not disorientated by its presence in the space
  • Fire and smoke resistant pass-doors can be incorporated

A5. Fire Resistant Staircase:

  • Insitu or precast concrete stairs
    • Stairs can be insitu or precast concrete and fire resistant
    • Thickness of concrete cover to embedded reinforcement determines the fire resistance period
    • But to avoid fire flanking from one flight to another by-passing the treads, landings and balustrades the stair needs to be in an enclosure or shaft with close fitting walls around and between the flights.
    • If a fire was raging on one floor the fire could heat the concrete and eventually make the treads of the flights and landings too hot to stand on.
  • Steel stairs
    • Stairs can be steel plate and fire resistant
    • Thickness of steel plate determines the fire resistance period but this would be limited until the steel is hot and floppy when it will collapses
    • If a fire was raging on one floor the fire could heat the steel and eventually make the treads of the flights and landings too hot to stand on and escape down
    • To avoid fire flanking from one flight to another by-passing the treads, landings and balustrades the stair needs to be in an enclosure or shaft with close fitting walls or more steel plates around and between the flights
    • Intumescent paint coatings could offer come insulation to the underside to help reduce the risk of hot feet but I have not heard of intumescent paint being promoted to do this
    • Intumescent paint coatings on top would make it a difficult stair to escape down with foamed treads and landings
  • Timber stairs
    • Stairs can be softwood with plasterboard soffits with or without carpet top
      • They only offer 30 minutes escape period
    • Stairs can be solid timber stairs and could have fire resistance
      • Possible materials: solid wood, dowelled solid wood, Cross Laminated Timber (CLT), Glulam
      • Timber is combustible but it can char and create a protective layer
      • Charring occurs at know rates and a timber section can be determined for strength and made thicker, wider, larger to allow for charring rates
      • Glued or dowelled or composite sections can burn more rapidly than solid timber and an allowance must be made for this.
    • Timber will act as an insulator and last longer before it is too hot to walk on
    • Stairs as part of a means of escape must have low surface spread of flame See A1 above.
      • Surface impregnations and surface coatings can provide this property to timber
    • Glass stairs
      • Laminated glass stairs is possible, the plastic interlayer between sheets bonds them together for greater strength.
      • Toughened glass can shatter into small rounded nuggets rather than long sharp shards and fall out of the staircase and fall safely. But it will not contain a person so is not permissible.
      • Laminated glass must be edge restrained so if a person crashes into the glass and it shatters the laminated glass is held together and in place and contains the person on the landing or flight
      • Radiant heat passing though glass onto a means of escape is not permitted
      • Laminated glass Interlayer can have Intumescent properties to become opaque to the heat of flames offering fire protection to people in the means of escape route.
      • Glass is low surface spread of flame and non-combustible
      • I have never heard of a stair using intumescent laminated glass for fire insulation
    • Plastic stairs
      • Not recommended and may not be permitted
      • Plastics are fuel in a fire
      • Plastics generate toxic smoke in a fire, normally smoke kills people, rather than the fire, in most cases
      • Plastics can generate burning droplets in a fire can spread the fire and smoke to other floors or burn people, plastics can stick to skin, and can be difficult to extinguish
      • Plastics can be modified with chemicals to suppress fire reactions
      • Be sensible, don’t throw your time and energy trying to make plastic stairs

A6. Fire resistant glazed enclosure:

  • Visit the British Library, Euston west of St Pancras Station, London
  • The Kings Library, a donated collection must remain on public display, came from one room of the British Museum
  • It is now located near the cafe and restaurant and displays the collection of books to all visitors, the book’s bindings face outwards so they are visible to visitors
  • It is enclosed in a 7 storey 2 Hour Fire Resistant (Integrity and Insulation) Curtain wall that can resist a ceiling mounted cleaning cradle bumping into it.
  • Steel is non combustible and fire resistant and used in place of aluminium framing
  • The glass is also sprinkled by water in a fire so must be able to be hot and resist the thermal shock of being cooled rapidly without loss of glass integrity in the curtain walling.
  • There are bridges and fire resistant doors (same performance as the curtain wall) for staff pickers to enter, it is accessed by book trolley lift and pedestrian stairs.

A7. Fire resistant glazed enclosure and stairs

  • Means of escape stairs internally need to be protected from fire
    • A glazed enclosure with integrity and insulation is very expensive;
    • Concrete, masonry or plasterboard partitions are cheaper
  • Means of escape stairs externally need fire protection from flanking fire
    • Non combustible material cladding can provide the protection
    • Distance can provide the protection
  • Accommodation stairs
    • A fire resistant enclosure around an accommodation stair is not normally required
    • If an enclosure is provided and the stairs may to be used in a fire you might consider making them a safe means of escape even if the Building Control Officer does not require it.
    • In this event an accommodation stairs within it own means of escape enclosure will need to discharge to a place of safety; not into the ground floor space but to the outdoors.
    • Preventing people using an accommodation stairs is impossible unless a retractable fire curtain drops around the stairs making it invisible and inaccessible. See A4. above

A8 Glazed enclosure to Means of Escape staircases

  • Communal stairs can:
    • serve multiple corridors at many levels serving multiple apartments, maisonettes and flats
    • offer designers an opportunity to articulate a terrace of blocks of apartments emphasising the stairs
    • be external and subject to weather See A2 External Means of Escape Stairs
    • be internal enclosed in curtain walling or structural glass assemblies and visible externally
  • Communal stair glazed enclosures:
    • Offer an opportunity to protect the stairs and its from the weather, winds, rain, snow and ice
    • Offer an opportunity to warm the spaces with solar heat gains in winter
    • Run the risk of overheating in summer
    • There needs to be means to ventilate towards the apex to let heat out
      • (preventing rain/snow entry)
    • There needs to be means to ventilate at the base to let fresh air in to replace the heat escaping
      • (preventing burglar entry)
      • not relying on doors (used to prevent burglary entry)
    • This ventilation does not want to be permanent but variable according to conditions
      • It may be automated, thermostatically triggered actuators
      • It may be manually operated

Brian Murphy BSc Dip Arch (Hons+Dist)

  • 01733 238148
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aka BrianSpecMan
14th March 2019 – 7th April 2019

Fire Resistant Staircases Q+A
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