Smokeproof enclosure

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In building safety and construction, a smokeproof enclosure is a type of exit stairwell that has been designed to keep out smoke (and other combustion products) in the event of a fire, so that building occupants may more safely exit the building.^[1]^[2]^[3]^[4]^[5]

Description

Rather than entering the stairwell directly from the building interior, one enters a smokeproof enclosure by means of an open-air balcony or alternatively, a so-called open vestibule, and proceeds thence, to the stairwell itself.^[1] The way that the balcony or vestibule is ventilated divides smokeproof enclosures into two basic types: mechanically ventilated which is not actually a smokeproof enclosures, where the vestibule and stairwell are ventilated by mechanical equipment, and naturally ventilated open air smokeproof enclosures where the open balcony or vestibule [or the stairwell] has openings directly to the outside of the building. This is the only type of the original concept of a smokeproof tower (i.e.: smokeproof enclosure).^[6]^[3]

US requirements

Under United States building codes, the stairwell of a smokeproof enclosure must have walls with a 2-hour fire resistance rating and vestibule doors (if provided) with a 1.5 hour fire resistance rating.^[7] The Life Safety Code states that such stairwells be "approved systems with a design pressure difference across the barrier of not less than 0.05 in. water column (12.5 Pa) in sprinkled buildings and 0.10 in. water column (25 Pa) in non-sprinkled buildings".^[4] Approved, in the Life Safety Code, means the committee didn't want to 'decide' so, left it up to someone else to decide a particular issue.

In the so-called mechanically ventilated smokeproof enclosures, the stairwell is positively pressurized relative to the rest of the building.^[6]^[8] This ensures that even when access doors are opened, smoke will not enter the stairwell.^[8]^[4] Of course, a higher pressure within a stairwell makes it harder to open doors from the building interior to the enclosed vestibules and to the enclosed stairwell.^[9] The Life Safety Code requires that the pressure differential across the barrier not be so great as to prevent the door from opening with a force of 30 lbf (133 N) at the door knob or handle.^[4] These 'pressurization' problems are, of course, non-existent with naturally ventilated smokeproof enclosures.

The fans and air ducts used to pressurize the stairwell are life-critical systems, and are required to be enclosed in non-combustible, likewise two hour rated, construction.^[4] (For fully sprinkled buildings, the required rating is just one hour.)^[4] The fans must be connected to an emergency power supply, and capable of both automatic activation by various fire and smoke detectors, and of manual activation by a central command post or by the actuation of a general fire alarm.^[4]

References

^ ^a ^b Bush 1988, p. 328.
^ Lathrop 1993, p. 83.
^ ^a ^b Scott 1997, pp. 201–202.
^ ^a ^b ^c ^d ^e ^f ^g Burke 2008, pp. 265–266.
^ Chowdhury 1999. sfn error: no target: CITEREFChowdhury1999 (help)
^ ^a ^b Clet 1978, p. 113.
^ Allen 2004, §5.2.3.
^ ^a ^b Binggeli 2011, p. 68.
^ FIPP 2012, pp. 235.

Sources

Allen, James Elmore (2004). Assisted living administration: the knowledge base (2nd ed.). Springer Publishing Company. ISBN 978-0-8261-1516-4.
Binggeli, Corky (2011). "Structural Systems § Exit Stairs". Building Systems for Interior Designers (2nd ed.). John Wiley and Sons. ISBN 978-1-118-17432-6.
Burke, Robert A. (2008). Fire protection: systems and response. CRC Press. ISBN 978-1-56670-622-3.
Bush, Vincent R. (1988). Handbook to the uniform building code: an illustrative commentary. International Conference of Building Officials.
Clet, Vince H. (1978). Fire-related codes, laws, and ordinances. Glencoe Press fire science series. Glencoe Publishing Co. ISBN 978-0-02-471760-3.
Fire Inspector: Principles and Practice. Jones & Bartlett Publishers. 2012. ISBN 978-1-4496-5527-3.
Lathrop, James K., ed. (1993). Life safety code handbook (5th ed.). National Fire Protection Association. ISBN 978-0-87765-379-0.
Scott, James G. (1997). Architectural building codes: a graphic reference. John Wiley & Sons. ISBN 978-0-471-28655-4.