Fire escape stairs

These are a more familiar pattern and where iron and steel are still employed in fabrication. The traditional construction relies on steel strings (formerly plate) with angle supports for cast-iron fretted treads, often strengthened by castings for the risers (Figure 1.2a). In the USA the external fire stairs are part of the vernacular architecture in the inner city (Figure 1.2 b). They are sometimes considered as an integral element of the façade (as on Hallidie Building, Figure 3-22), instead of becoming the visual accident that is commonplace- The American approach to fire escapes is more dramatic owing to the hinged security steps for the lowermost flights-

Fire escape construction is generally a mundane affair, with column supports for framed landings and dog-leg flights spanning as infill (Figures 7-2c and 7-2d). Detailing with structural sections requires skill to overcome clumsiness at connecting points- Salvisberg's detailing is exemplary in the instance chosen where members are splayed or cut to ensure a neat geometry- The construction

Cast iron grid An9le frame to tread

Figure 7.2a Ladders and fire escape stairs: Details of traditional cast-iron and steel treads and risers

Cast iron grid An9le frame to tread

Figure 7.2a Ladders and fire escape stairs: Details of traditional cast-iron and steel treads and risers is conventional using 12.5 mm plate for strings and 105 mm x 105 mm tees with tubular rails (Figure 7.2e). Arne Jacobsen has solved the problem of an obtrusive external stair by encasing in a cylinder of fire resisting glazing (Figure 7.2/).

Security can be effected by caging the fire stairs with exit gates at ground level (Figure 7.2g). The requirements of fire officers will include emergency lighting, fire resisting glazing to windows within a prescribed distance and weather protection unless heated treads are provided.

In the UK external steel escape stairs are subject to licence and therefore regular inspections are needed to check on condition and repairs. Galvanizing the iron and steel components of the structure will prolong their life, delaying the paint treatment by ten or so years will increase the bond between paint and the zinc-coated surfaces.

In the Centre Pompidou, Paris, the principal movement areas are totally contained within the building envelope, whilst emergency routes are largely external. Space is generally the problem but at Stockley Park there is an elegant solution for secondary external stairs (Figure J.2h) which can be bolted onto façades as required.

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