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Fire Protection Engineering and Sustainable Design
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Fire Protection Engineering and Sustainable Design
Why performance-based design will become increasingly important in the future

By Simon Dent | Fire Protection Engineering

In the 21st century, sustainable building design is an increasingly popular and important client requirement as well as a growing focus for professional engineering firms. For the fire protection engineer, integrating sustainable, or "green," building design aspirations presents the challenge of resolving conflicts between architectural vision and code expectations for fire safety.


At the heart of fire protection engineering is meeting the challenges of clients' innovation. It is often the case that the fire protection engineer contributes to a broad spectrum of building solutions that significantly affect many other members of the design team.

 

By discussing the challenges that fire protection engineering must overcome to support sustainable building design, this article seeks to embellish on a simple philosophy " that the fire protection engineer's use of performance-based design can both liberate the design team from code restraints, which might other wise hinder the building's sustainability rating, and serve to address the more holistic aspects of true sustainability.

 

SUSTAINABLE BUILDING DESIGN: A MULTIDIMENSIONAL CHALLENGE
In order to understand the implications of sustainability for fire safety, it is first necessary to understand what is really meant by "sustainable building design."

 

In the first instance, a sustainable building is the physical end product of a design philosophy to improve the "performance" of the built environment by increasing the efficiency of the resources used in building during its lifecycle: construction, operation and demolition. Such performance is typically measured through a range of international environmental performance-rating systems for buildings.


Widely recognized rating systems include: BREEAM, the Building Research Establishment Environmental Assessment Method most commonly used in the UK and increasingly internationally; LEED, The Leadership in Energy and Environmental Design Green Building Rating System developed in the United States; and Green Star, a similar rating system used in Australia.

 

All of the systems are fairly similar in their approach, with scores for the incorporation of sustainable design under areas such as energy, water, pollution and waste. The higher the total building score the more sustainable the design is considered to be.

 

In the second instance, a truly sustainable building is also a socially sustainable one; that has a positive social impact on the local environment for the duration of the building's existence. Wider issues such as societal needs, maintenance of heritage, provision of social amenity, accessibility for all and future-proofing of a building so that it continues to be useable for a longer lifespan than a more conventionally designed building can all be considered.


BUILDING SUSTAINABILITY AND THE FIRE PROTECTION ENGINEER
Clients' design aspirations and tenant demands increasingly lean towards the provision of large open floor plates, the incorporation of open atria and the interconnection of spaces and stories. These approaches maximize a building's bright and airy feel of daylight and natural ventilation while being harmonious with the principles of sustainability.

 

This desire for open planning alone presents the fire protection engineer with a concept design that is at odds with most international building codes that seek to limit large open compartments and the interlinking of floors. Achieving a "good" or "excellent" rating is often required for funding, good corporate governance, or for attracting tenants and premium rental returns; therefore, the design team seeks to achieve quantified reductions in the use of resources such as energy and water. Fire protection engineers, as part of these design teams, must rise to the challenge of contributing to these reductions without significantly compromising the client's aesthetic requirements, or the resulting level of fire safety.


Natural lighting from large open spaces and glass facades can provide benefits in reducing energy consumption while increasing population well-being and productivity when compared to artificial lighting alternatives. Despite the restrictions of building codes, engineered solutions can make these designs (which also require less use of fire compartmentation) feasible. Through the assessment of the fire load within the space, fire protection engineers can assess the smoke movement through interlinking spaces and develop technical solutions to address this while also tailoring the solutions towards a low energy, natural ventilation strategy. Additionally, the engineered provision of elements such as active smoke or fire curtains can provide the code-required barrier between, for example, an atria mezzanine and an adjacent escape route.

 

In order to quantifiably reduce a building's resource use, fire protection engineers also need to think about the resource demands of products necessary to achieve the required fire safety performance.

 

Despite refurbishment projects' obvious relationship to the sustainable philosophy of re-use, recycle, they present the greatest challenge to providing adequate levels of performance for both fire and sustainability. These buildings also present a challenge to code officials, as the buildings rarely comply with the current standards. For refurbishment, the best approach is performance-based engineering - understanding how the building currently performs and finding appropriate solutions working with the building's current provisions to achieve acceptable levels of safety. Considering embodied energy, it is far more sustainable to reuse existing buildings. Through good design, it is possible to do so far into the future.


SOCIALLY SUSTAINABLE FIRE ENGINEERING
Aside from the client-driven challenges, there are other aspects that relate to sustainability that are likely to become stronger influencing factors for designs of the future - such as the actual population of the buildings.

 

A global trend towards aging populations and longer working lives means sweeping code assumptions that building occupants are generally mobile are becoming less appropriate. Typically, greater provision is made where, for example, it is known that a building is designed to accommodate a high proportion of wheelchair users.

 

The issue of obesity, and the challenges it poses to fire safety are perhaps felt most acutely in hospitals and treatment centers.

 

Flexible working and the increased focus on maintaining a healthy work life balance is also presenting new challenges and opportunities. As flexible working becomes a more popular approach, businesses are increasingly designing fit-outs without dedicated desks, with occupant's hot-desking or using flexible spaces for their activities. This, combined with the understanding that many offices are generally only occupied to 70% capacity with people on leave, out at meetings, etc., provides an opportunity for businesses to actually lease less space than they would if everyone had a traditional desk. This may result in more people being allocated to work in a building than say the exit width can accommodate, although the actual population at any point in time should be no greater than can be evacuated safely. The challenge for the fire protection engineer is to test whether or not that is true and possibly to design for more people than simple floor area calculations would imply. This is particularly relevant where a building may cater for trading floors, or changing its use from an office to education, as is happening in many city centers.


Increasing flexibility and minimizing business loss also improves sustainability. Sprinkler protection of buildings, although using resources, can be seen as inherently improving sustainability both for flexibility and as they reduce the potential size of polluting fires. Residential sprinkler protection, particularly in higher risk occupancies, can be argued to be socially sustainable as they reduce risk of loss to life and property and protect some of the most vulnerable members of society.

 

Some of this may appear to lead to overly conservative designs and hence not be sustainable; however, if future flexibility can be increased, the lifespan of a building can be increased and hence its sustainability. All of these decisions should be made by the client, and the fire protection engineer can help provide their clients with information and options.


Simon Dent is with Arup.

 

References:

  1. Building Code of Australia, Australian Building Codes Board, Canberra, 2009.
  2. NFPA 101, Life Safety Code, National Fire Protection Association, Quincy, MA, 2009.
  3. McGrattan, K., et al. Fire Dynamics Simulator (Version 5) User's Guide, NIST Special Publication 1019-5, National Institute of Standards and Technology, Gaithersburg, MD, 2009.

Case Study 1: Stockland Head Office
Sydney, Australia

THE BRIEF
The client's objectives for their new head office were to:

  • Create connectivity in their business to break down internal silos.
  • Showcase excellence in environmentally sustainable design for a tenancy in an existing building.
  • Meet time and budget constraints.
  • Minimize disruption to other tenants in the building.

PROJECT APPRECIATION
Stockland's new head office is an eight-story tenancy on levels 22-29 of an existing 32-story office building in Sydney's central business district. The original building was a typical 1980s high rise, with a central core and floors separated from each other.

To respond to the business and environmental needs of the client, the architect developed a concept for interconnecting the eight stories with an open atrium, circulation stairs and two fire isolated escape stairs.

 

LIMITING THE VISION
To minimize fire and smoke spread, the Building Code of Australia (BCA)1 allowed the provision of only two stories to be interconnected via open stairs. The code alternative was to design an enclosed atrium requiring glazing and wall wetting sprinklers to separate the floors from the void. This did not meet the desire for real interconnection in the tenancy.

 

THE INNOVATION
To allow an open atrium and stairs, as shown in Figure 1, various options were explored using performance-based design. Options included smoke exhaust and the use of vertical fire curtains surrounding the atrium on six floors; however, there were issues with cost and practicality.

 

It was finally decided that the design would feature a horizontal fire curtain. The curtain serves to seal off the atrium in the event of fire by incorporating a fire-rated flexible fabric that is carried on thin wires across the void. The concept used curtains at levels 25 and 27, essentially reintroducing the fire compartmentation given by the previous floors. Figure 2 shows an elevation view of the design. Vertical curtains were used to close around the accommodation stair. Risk assessment techniques were used to demonstrate that a 3-level interconnection achieved an acceptable level of performance. The risk assessment also addressed failure of the operable curtains.

 

COMMUNITY, ENVIRONMENT AND SOCIAL CONSIDERATIONS
The project showcased what could be done with existing building stock, both in achieving an exciting new work environment and in achieving excellence in environmental performance.

 

Reuse of a building is far more environmentally responsible than development of a new one, but it can be a significant challenge. The environmentally sustainable design for this tenancy, as well as the business objectives for Stockland, hinges on the creation of the open atrium. Without the fire protection engineering design to allow the open atrium, these objectives simply could not be achieved.

Case Study 2: California Academy of Sciences
California, USA

THE BRIEF
The client's objectives for their Academy were to:
  • Design a working research facility with the capability for unlimited storage of specimen samples. The samples were to be contained within combustible preservative within movable storage cabinets (compact shelving).
  • Create a unique rainforest exhibition, effectively a "building within a building" incorporating multiple levels of interconnectivity.
  • Safeguard 18 million samples of plants, animals, fossils and artifacts - essential tools for comparative studies on the history and future of the natural world.

PROJECT APPRECIATION
The 41,000 m2 sprinklered building shown in Figure 3, features an undulating 1.01 ha living roof. Other important architectural features include a perimeter steel canopy supporting photovoltaic cells, a large glass skylight supported by a tensile net structure and a 28 m diameter glazed dome, housing a rainforest exhibition. The new $484 million CAS opened to the public in September 2008.

 

LIMITING THE VISION
In the United States, performance-based fire safety is generally accomplished under the guise of the prescriptive building codes "alternate materials and methods of design" clause. In the CAS, more than a dozen such performance-based design equivalencies were proposed and accepted.

 

For example, the NFPA suite of codes2 do not normally permit multiple levels to be atmospherically interconnected without smoke exhaust. However, interconnectivity between multiple levels was a client requirement for the rainforest exhibition dome. Achieving smoke exhaust from the rainforest dome would be architecturally undesirable and physically difficult to implement, as the dome itself is located within the larger CAS building.

 

The ceiling of the main exhibit hall required special treatment in order to avoid the cavernous echo that might occur with such large spaces. In this case, 0.5 meter x 0.5 meter square panels were suspended approximately 2 meters below the concave main exhibit hall roof to help dampen the echo. Under the curved roof, the panels needed to appear "free floating" or disconnected from each other. This resulted in a 12 cm gap (approximate) between each panel. In the event of a fire underneath, this free-floating collection of ceiling panels with associated gaps would not permit a normal ceiling jet to form. The plenum space above them was the entire area of the exhibit hall, which meant that a hot layer could take significant time to develop. Because of this geometry, there was a concern that sprinkler operation would be significantly delayed.

 

The client's requirements for a working research facility also provided a great challenge. The required design has no similar precedents and was therefore not addressed under generic code guidance.

 

Normally, due to the hazard type (preservatives with >70% alcohol content), the code would require an automatic sprinkler system with secondary containment of combustible spills and fire suppression water. This would prove a big burden in terms of drainage implications.

 

THE INNOVATION
For the research facilities, high pressure water mist systems were investigated. The design required a peer review and full scale fire testing. Fire tests were performed to prove the theoretical performance of the mist system design. The results were a success.

The proposed suppression system successfully incorporated a greatly reduced water flow rate - thus the design precluded the need for special drainage and containment systems.

 

The client's requirement for a multilevel rainforest exhibition could not be achieved through the normal use of smoke exhaust. Using performance-based design tools and computer-aided fire and egress analysis, the fire protection engineers were able to verify the safety of the egress strategy within the rainforest exhibition without smoke exhaust.

 

Fire Dynamics Simulator3 was used to model a likely fire scenario - the results of which were compared to an egress analysis model to ascertain an appropriate evacuation time within tenable limits. The approving authorities reviewed the results and approved the rainforest design. The fire protection engineering analysis saved the architectural integrity and satisfied the client aspirations for an immersive rainforest experience.

 

FDS modeling was necessary to determine whether the sprinklers within the exhibition hall would activate within a reasonable amount of time. A solid ceiling model was compared to the proposed ceiling. The resulting strategy included the spacing of the sprinklers in a more dense arrangement to have the confidence that they would activate within the same time frame as that of a standard design. This work saved the architectural integrity of the entire ceiling.

 

The engineering work provided a safe environment, maximized space savings and benefited the building functionally and aesthetically. It provided savings with regard to initial installation costs and future service and maintenance costs projected against the building's life cycle.



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