Descripción textual de los casos de uso del sistema

Basic Building Safety Building codes Building integrity

A prime responsibility of architects is that of designing out dangerous conditions.

Overwhelmingly, we’re concerned with what happens in the event of fire, but life safety also covers a variety of daily issues such as falls, collisions, and air quality.

Most of these issues are covered by local building codes. These are ordinances adopted into law by municipalities, counties, states, or nations that typically prescribe various parameters of building performance. Public authorities have an interest in making sure that buildings don’t present undue hazards, both to their citizens and to their emergency response entities. Europe tends to oper-ate by national codes, while America has long had a tradition of local author-ities making their own code (e.g., Chicago and New York), or adopting one of a number of commercially available building codes, often with some modifica-tions to take into account local condimodifica-tions.

This panoply of code information can be daunting. However, a design that understands the fundamental performance requirements of buildings in emer-gency situations will often meet the code just by adopting a logical approach.

Indeed, there is a movement in some countries away from prescriptive codes, which require buildings to be designed to a rigid set of dimensional and mater-ial criteria, and toward performance-based code compliance, which require designers to assert that their designs will perform correctly. While this adds liability to the design team, it allows for great flexibility in approaching life safety issues, and is likely to lead to better solutions through evolution. Codes typically change in response to disasters, while performance-based solutions often evolve during design.

In addition to government-based building codes, there will often be a number of codes both written and unwritten to which building designs must comply.

Worker safety may be mandated by unions or by government labor departments.

Buildings for a particular purpose – laboratories for example – may be subject to design guidelines from public or institutional entities. Finally, insurance companies may require policy holders to design to standards beyond those of building

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codes. In fact, insurance companies have often been at the forefront of code development. While architects will often be responsible for ensuring that their designs meet the letter of these formal and informal regulations, it is again the spirit of the codes that we think is most important, and this chapter will focus on broad principles rather than modeling itself after one particular code or another.

Life safety – the basics

Our overwhelming life safety concern as architects is fire. Over 3000 Americans typically die in house fires each year, and fire can kill or injure by both burning and (more commonly) asphyxiation. Unfortunately, many of the same qualities that make our buildings work – partitioning, enclosure, and security, for exam-ple, make them more dangerous in a building fire (Figure 2.1.1).

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Figure 2.1.1. Building fires – especially in multi-story buildings – are usually the gravest danger facing occupants. Building integrity, occupant notification, containment, suppression, and escape are all designed to minimize the potential for death and injury in the event of a large fire.

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1-3 Fire separation Sprinkler

Fire separation door

Activity rate

Clear signage

Visual and audible alarm Doors open outward

Travel distance 250 ft/300 ft

We generally have four strategies for ensuring that occupants in our buildings face minimal danger from fire (Fig. 2.1.2). First, we concentrate on building integrity, that is, making sure that the building’s structure and fabric continue to perform during a fire. Second, we lay out buildings to provide containment, preventing the fire from spreading uncontrollably. Third, our buildings must notify occupants of the dangerous situation, and fourth, the layout must enable occupants to escape the danger quickly and safely.

Building integrity involves the selection of materials and systems that maintain their protective and functional characteristics even in the event of a major fire. Generally, larger-scale buildings will require more robust materials, while smaller buildings permit more flammable construction. Codes require certain types of construction based on the anticipated use of the building – often referred to as the occupancy type – as well as the building’s size and/or height.

The more dangerous the building type, or the larger or taller the building, the more conservative the code is likely to be. This logic accepts that a fire in a small building (e.g., a house) may present a much greater danger to its much smaller number of occupants.

The level of integrity for a given type of construction is measured in hours.

This suggests the amount of time that a particular structure or component

Figure 2.1.2. Basic strategies to minimize the danger of fire in buildings.

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Figure 2.1.3. Building integrity mandates protective coverings for vulnerable structural materials. Steel is a particularly difficult problem, as it loses its strength in extreme heat conditions. Standard approaches to its protection include spray-on fireproofing, encasement in gypsum wallboard or plaster, and surrounding steel members with concrete.

will survive a typical building fire, however in practice this may not arise directly from testing. Materials and their typical performance rating are given in Table 2.1.1. In addition to rating components by hours, some codes will further distinguish between ‘non-combustible’ and ‘combustible’ construc-tion, essentially dividing types into those that provide fuel for fire (wood) and those that don’t (steel and concrete).

Steel presents particular issues of building integrity (Fig. 2.1.3). While it will not ignite in building fires, it is susceptible to softening and eventually melting Table 2.1.1. Typical values for fire ratings of common building materials.

Material/Assembly Fire rating (hrs)

Timber or metal studs with one layer of gypsum wallboard 1 each side

Timber or metal studs with two layers of gypsum wallboard 2 each side

Three layers of gypsum wallboard with embedded metal studs 3 Single layer of 225 mm (8
) Concrete Masonry, fully grouted 4 Single layer of 100 mm (4
) hollow clay brick (200 mm total) 1.5 Double layer of 100 mm (4
) hollow clay brick (200 mm total) 2.5

154 mm (6
) poured concrete 4

89 mm (3.5
) concrete slab 1

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