Lawrence Webster Forrest (LWF), Fire Engineering and Fire Risk Management Consultants
Lawrence Webster Forrest (LWF), Fire Engineering and Fire Risk Management Consultants



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Lawrence Webster Forrest
Legion House
Lower Road
Kenley
Surrey
CR8 5NH

Tel: +44 (0)20 8668 8663 Fax: +44 (0)20 8668 8583
E-mail: fire@lwf.co.uk

Case Study: Madrid Xanadu Shopping and Leisure Centre - Smoke removal, fire engineering

As an introduction to performance based Fire Engineering in Madrid, Spain, LWF have developed a solution for a large open retail shopping centre. The design investigates the pro and cons of smoke removal methods, looking at improving base fire systems to eliminate the need for more onerous demands of fire rating and travel distance limitations.

Project Description and Application

Introduction

In 2002, LWF were appointed by project managers MACE to work with the design team on a new retail and entertainment complex. The development of a commercial retail and leisure complex is part of the new two storey Xanadu Shopping Centre, Madrid, Spain, accessed from the N5. The base design of the fire safety strategy had been completed by other engineers, to meet strict adherence to Cepreven and Normative requirements. LWF were then asked by the project managers to investigate the possibility of an alternative solution. Current legislation has no mechanism available to undertake such an approach.

The Project

Madrid Xanadu is located approximately 23km Southwest of Madrid, near the town of Arroyomolinos. The commercial centre is located within an area designated as Parcela 2 of the Parcel plan SAU-6 Monte de San Martin. The Parcel 2 shall be developed to accommodate the commercial centre, exterior service areas, exterior pedestrian circulation, landscaping, signage, lighting and parking for approximately 7300 vehicles.

The project in question is the development of a two level retail shopping and leisure centre. The design incorporates the common characteristics of a shopping mall with retail shops varying in size from approximately 35m2 to in excess of 3000m2. It is the design intent of such complexes to provide an open feeling to the space and therefore the provision of a multitude of fire separations is an impractical means of achieving a fire safe building, rather, active fire safety systems are employed to undertake the role.

The central concourse, or street, of the mall provides the primary access points to the shops on both the ground and first floors. To encapsulate the open feeling of the centre, the street is a double height space with connections through the floor.

The shopping mall itself, excluding the major tenancies which are attached, has an occupant capacity of just under 10 000 persons.

The gross floor area of the developments is 159, 321m2.

Fire Engineering Challenges and opportunities.

As the approach of performance based Fire Engineering is not described in the Spanish regulations, the first consideration was to identify the approach proposed for consideration by the project team for consultation with CAM Bomberos. As this is part of the first such project in Madrid that has followed deviations from the normative with engineering justifications, communication of the process was a key element for a successful design.

The benefits of Fire Engineering is that the solutions do not come from a black box, but the specific risks and demands from each independent building can be considered from both the perspective of the buildings contents (fire risks) and occupants (egress and human behaviour).
The approach was supported by engineering assessment which utilised computational fluid dynamics computer models, zone models and fundamental first principle hand calculations for smoke removal and egress flow.

From our initial review of the prescriptive design proposal it was apparent that the following elements of specific fire engineering could be considered:

Extending the allowable travel distance from the building.

Specifically considering the deletion of sprinklers from the high roof area of the food court.

Allowing for an increase in smoke reservoir size beyond the limits of the 2000m2 and 60m length, limits imposed by the normative smoke design guidance documents.

Revising the degree and level of fire rating within the building.

Changing the method of smoke control from specified shops from either natural ventilation or provision of 180min fire rating to either mechanical smoke exhaust or a smoke barrier.

To address all these issues necessitated an alternative fire engineering approach using performance-based solutions particularly in respect of the movement of smoke and the safe evacuation of occupants.

The practical application and approach

Increased travel distance

To justify the increased travel distance of an additional 31m, an Available Safe Egress Time (ASET) Vs Required Safe Egress Time (RSET) assessment was undertaken where the RSET considered all the required factors including pre-movement of occupants. Rather than using the sophisticated visual graphic tools, hand calculations were used to present the calculations since this was a new concept to the approval authorities it was important to outline how answers were derived. As with smoke modelling a practical consideration of the evacuation simplified the scenario.

Computer modelling of smoke movement

In order to exceed the limitations imposed from design guidance on the smoke control system a computational fluid dynamics assessment was undertaken to track the movement of smoke in event of a fire scenario. The simulation was a virtual reality of a fire in a shop and the resulting smoke spreading through to the adjoining smoke reservoir, transversing along the length while venting out to atmosphere. This process was necessary, as it is the only was to demonstrate with confidence the acceptance of the variation.

Deletion of sprinklers

It is recognised that the higher a ceiling will be the longer it will take for a sprinkler head to activate. A high two storey portion exists in the food court, but rather than state it is too high to be effective, which is debatable, an actual fire scenario using engineering tools was undertaken to determine the activation times of sprinkler heads and the temperatures that would be imposed on surrounding structure and fabric from a fire underneath. The assessment showed through engineering that the objectives set out to be achieved could be met without the provision of sprinklers in this area.

Fire rating

Part of the original design requirements imposed the need for 180min fire rated shutters to be installed in the front of specified shops. As part of a holistic review of the fire systems for the building, ICS Forrest focussed on improved systems in the building that were either existing or proposed. Items considered were voice activated warning systems, addressable smoke detectors, fast response sprinkler heads, sprinkler tanks on site and inherent benefits from large spaces. The engineering assessment justified a reduction from 180minute fire rating to the provision of automatic smoke curtains.

Method of smoke control

The current legislation requires that smoke control measures for new buildings be addressed by natural as opposed to mechanical means. Following meetings with the Bomberos the background and concerns with automated systems were highlighted. LWF then approached the issues individually considering the overall risks and reached agreement that mechanical systems may be utilised. Subsequently it is intended that the local legislative requirements will be altered to reflect the changes. Unfortunately, due to the stage of development before agreement could be reached, the systems adopted were natural.


Presentation of documents for the design and construction

A fire engineering report was produced following the principles of draft British Standards which are being developed at the same time as a European Standard.

When producing the report it was strongly felt that clear and concise deliverables are the key to all successful projects. The most cutting edge fire engineering designs can fail if not properly presented and transcribed into a solution that is easily understood. Therefore great effort was put into the report to ensure that the client, design team and CAM Bomberos not only understood the strategy proposed but also bought into it.


Conclusion

Although guidance for such facilities was available, it was found through alternative fire engineering that amplification of some of the base fire protection features and utilising inherent benefits from aspects of the design such as the materials of construction and wayfinding a more effective and economical solution was developed.

The solution also fitted in with design flair and options to allow for visual features that would be spoilt by fire safety systems such as smoke curtains and fire doors.

The solution was developed by consultation with all parties including the Bomberos. The documentation had no hidden information, by following such a process enabled no surprises and understanding between all parties during the process of the expectations. This approach may seem idealistic but has been developed after years of experience as a way of mitigating risks to the client.

As a result, an estimated saving in the order of 250,000 euros was saved on the project and a solution more suited to the environment was adopted.

Key Benefits

A solution was developed which saved an estimated 250,000 euros on the project cost.

Design options that were complimentary with the visual and architectural desires for the development, as opposed to prescriptive design requirements leading the way.

The involvement with the Bomberos and constant dialogue were important to assist in providing a fluid approval process for this new concept of performance based designs.

Engineering as opposed to negotiations. Concise, clear and accurate documentation that is easily understood and stands as a record in years to come of decisions made and reasons for actions.

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