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: Snowdome, Madrid - Alternative Fire Engineering approach, evacuation model

In a pioneering introduction to performance based Fire Engineering in Madrid, Spain, LWF have developed a solution for an indoor skiing facility that throws away the old text book approach but develops a solution from first principles.

Project Description and Application

Introduction

In 2002, LWF were appointed by project managers CEM to work with the design team on a new entertainment complex that brings winter to Madrid, 365 days a year. The development of an indoor skiing facility, Snowdome, forms part of an overall retail and entertainment development as part of the new Xanadu Shopping Centre, Madrid, Spain, accessed from the N5.

The Project

The project in question is the development of a skiing facility for use by the general public comprising of the main skiing area (single story built on a slope) with associated changing facilities.

Administration accommodation is provided on an adjacent first floor level. There is also an adjacent restaurant/bar/discotech area that is linked to the main shopping complex development and the skiing area offering a panoramic view of the slopes while enjoying the warmth.

The design of the facility allows for a 240m long straight run from top of the slope to the chair lift base.

The ski area and plant occupy a gross floor area of 16,200 m2. The ancillary warm areas of the ground and first floor occupy approximately 3,000 m2.

The skiing facility will be designed for a maximum of 750 persons on the slopes alone. A total of three different levels of slopes exist served by a chair lift, rope tow or magic carpet. To create an alpine feel the interior of the ski dome has rock formations and trees to offer the full alpine experience.

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). Rather than simply negotiate a deviation from the normative requirements ICS Forrest took a fresh look at the project without reference to normative requirements to consider what the most appropriate solution for this form environment would be. The approach was supported by engineering assessment and calculations ranging from burning wooden huts to the movement of occupants with thick ski clothing trying to walk down stairs in stiff ski boots.

From our initial review of the development it was apparent that three fundamental issues existed, these being...

The building contents had very limited fire load when considered over the entire area. Localised risk areas existed which required specific considerations. Adoption of a fire rated structure, sprinkler system and smoke venting throughout would add little benefit to a safer environment.

Although the risks of fire could be managed, the occupants themselves would not follow a normal egress situation. Many people would be in a family environment therefore any emergency would prompt a gathering of family before evacuation. Occupants would be wearing thick heavy clothing, carrying skis, poles, snowboards, and trying to evacuate with their possessions. Footwear would comprise of stiff shin high boots that make descending steep stairs slow and dangerous. Occupants may be on a chair lift suspended in the air in event of an emergency.

Although the fuel load itself was limited the typical construction of cold environments incorporates wall and ceiling panels that potentially allow for a fire to spread within the cavity panels. The inappropriate choice of these panels in the past has resulted in the death of fire fighters in Europe.

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

A full 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 opposed to simply entering data into a computer model. As with smoke modelling a practical consideration of the evacuation simplified the scenario, as the number of converging streams of occupants was minimal.

Eventually, the differing fire scenarios were collated and assessed in comparison with occupant’s evacuation to demonstrate that the occupants could safely evacuate from the area in all probable fire scenarios.

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.

How the solution works

The final solution

The area was designed as one large compartment with a designated local area of automatic smoke control. This limited the number of penetrations through the insulated roof structure and minimised the degree of smoke curtains. The provision of more smoke vents were shown to be ineffective as the operation of the vents is based on warm buoyant smoke, in this case with the limited fire size and the cooling of the smoke due to the ambient environment, this natural occurrence was negated.

Rather than provide fire rating to the stairwells, which ran the length of the building, and fire rate the entire steel structure, localised areas were considered as appropriate to the risks with justification for elimination being based on the resulting gas and steel temperatures from various fire scenarios.

Although local standards allowed the use of certain wall and ceiling materials concern was raised on the fact that certain composite panel cores are extremely hazardous and yet are able to pass the test. This anomaly was discovered on investigation into the test set-up. As a result a safer environment has resulted by choosing a panel that limited the risk of adding fuel to any incident and concealing fire spread. This results in a safer environment for the fire fighters.

Rather than adopt a standard consideration for egress, the locations and sizes of the exits considered the nature of the activities by providing low but deep steps to accommodate the expected footwear. The locations of the exits matched the discharge points of rope tows and chair lifts and the descending skiers.

Conclusion

For a building of this function, little relevant guidance was available, and adherence to conventional codes would result in costly and ineffective measures being provided. This therefore reinforced the need to develop a fire strategy using a practical application from first principles and innovative flair to meet the objectives of life safety.

Fundamentally the strategy challenged the need for fire ratings to the structure, natural venting of smoke and finally, conventional egress designs. As a result the final solution focussed on the areas of risk and eliminated fire rating to most of the structure, removal of ineffective natural vents throughout the ski area by supplying forced ventilation in the area of risk and egress doors and positions that considered the location and thoughts of the building occupants.

As a result, savings in the order of an estimated 300,000 euros was saved on the project and a solution more suited to the environment was adopted.

3 Key Benefits

A risk and cost based solution has been produced for a development for which prescriptive codes were found to be inadequate, that meets the objectives for safety and effective use of the facility.

A solution was developed which produced savings in the order of 300,000 euros on the project cost.

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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