28 Apr Ensuring safety & connectivity
As the preparations for Expo 2020 continue to gain momentum the remarkable achievements in the transportation sector across the region still amaze, writes Peter Stephenson, Associate Director Buro Happold Engineering.
With multiple infrastructure projects improving the connectivity across the region and future projects coming on-line, it re-affirms the ambitions of the Middle East to connect the worldwide community: the Dubai Metro Extension and the Dubai International Airport projects are key for the success of the Expo 2020; when fully operational, Al Maktoum Airport will cater to between 160 and 200 million passengers annually and the Abu Dhabi Airport Mid-Terminal Complex completion will ensure a safe environment for the travelling public, staff and visitors demonstrated by having a robust fire safety strategy.
Fire safety challenges can be found in all large mass transportation buildings, such as airports and railway/metro stations, however there are few building types also requiring complex operational support systems to enable the building to function (retail, security, customs, baggage handling etc.) whilst safely ensuring a positive customer experience. Key architectural aspirations to optimise this customer experience encourages large open spaces for the public areas and efficient operational design for back-of-house areas.
This is a major challenge to be addressed within the fire strategy and requires consultation and input from all members of a design team and relevant stakeholders because once airside (i.e. departures), a passenger or object (such as luggage) has cleared security and is deemed safe for a flight departure. This boundary between airside and landside may be formed by solid walls, partial walls/screens, doors or simply a space occupied by staff and an x-ray/security equipment. The position of this demarcation needs to be understood, as it requires full consideration when developing the evacuation strategy, including the provision of directional escape signage and zoning of fire safety systems.
Civil defence access
In large terminal buildings and across the airport, the responding fire department/service typically require a single control point to receive a briefing from airport staff on their arrival at an incident to make an assessment prior to implementing their tactical response. From the access location(s), the first responders need quick and easy access to the incident floor from a protected route within a safe distance of the incident and with an adequate supply of water.
A Fire Command Centre (FCC) provides an operational hub within which it will be possible to receive live information from the life safety systems, including the CCTV cameras across the terminal/site. The command centre will be separated from the remainder of the terminal by fire resisting construction and should have a dedicated access route direct to open air.
The FCC should be provided with control panels for each smoke control and evacuation zone, which allows full control of an evacuation of the incident area. An evacuation can be phased on an automatic or manual basis, or the decision can be taken to simultaneously evacuate the entire terminal from the control room, if considered necessary. In addition, a microphone is provided with which direct announcements can be given to the building occupants.
The users of an airport terminal consist of a broad range of nationalities, mobility, family groups, single travellers, all with varied travel experience. Their key focus is on either a departing flight, or reclaiming their luggage on arrival and leaving the airport in a timely fashion. An understanding of this behaviour (particularly family groups) should be a key to a successful evacuation strategy.
With a focus on their process within the airport, and during peak times the high numbers of occupants being present, a simultaneous evacuation policy can be unrealistic and even unsafe. A phased approach, where a limited number of evacuation zones actually evacuate during an incident, is preferred. This requires that the remaining building zones are large enough to safely accommodate the anticipated occupancy level(s).
Prescriptive codes assume floor space factors, and resulting exit width requirements for egress. For airports, the occupancy is far more complex, and subject to detailed quantifying by the airport planning team. The fire safety engineer can therefore determine the egress requirements using passenger numbers that are based on the predicted passenger flow through the terminal as dictated by the scheduled arrival and departure of flights. The number of staff supporting the airport operations, as well as airline staff, must also be included, and these too are subject to peak flows during a working day.
The response of people within the building upon hearing an evacuation message is another factor that the design team must take into account, especially if an ASET (Available Safe Egress Time) vs. RSET (Required Safe Egress Time) assessment is being undertaken. PD 7974-6 (Human factors: Life safety strategies – Occupant evacuation, behaviour and conditions) describes items that will have an impact on the pre-movement time of occupants, which include the possession of luggage, presence of family groups, language barriers and security restrictions.
The potential for persons with reduced mobility, religious groups etc. should also be examined for local conditions to determine any additional requirements that would need to be included within the design. The key to all of the above is a competent, trained fire safety team and reliance on this is key to a successful airport fire design. In the absence of such competence, far less reliance on management must occur.
Fire strategy and fire engineering process
Airport and/or railway project designs may necessitate the adoption of a fire engineered approach as opposed to strictly following the recommendations of prescriptive code guidance. The framework contained in BS 7974 (Application of Fire Safety Engineering to the Design of Buildings) provides for the application of fire safety engineering and is similar in that regard to the processes detailed in other performance-based design guides. BS 7974 recommends four main steps in the design process, namely:
1. Qualitative Design Review (QDR)
2. Quantitative analysis of design
3. Assessment against criteria
4. Reporting and presentation of results
It is during the QDR stage where the parameters that influence the success of the final fire safety design are discussed and agreed. Any key items that are not identified during the QDR, can impact the design development and be a risk to the project. The team formulated to carry out this process should be led by the project fire engineer(s) and is key. The QDR Team should include representatives from the following areas:
• Client – including members of the security, retail, customs teams
• Architect who will understand the architectural aspirations of the client
• Engineering Teams including mechanical, electrical and plumbing, transportation, landscaping etc.
• Airport Fire Department for input into operational response, particularly airside
• Civil Defence as AHJ and responder to emergency incidents, particularly landslide operations
• Contractor (if appointed).
As part of this review BS 7974 advises that the architectural design and occupant characteristics of the building should be considered.
The passenger experience and interaction from first to last impression of the transportation hub is key to the architectural design aspirations. The fire strategy must complement this process and the resultant architectural design often consists of large and high open spaces front-of-house for the public, with little or no physical separation between each area. This presents numerous fire safety challenges but allows a smooth transition for passengers from area to area, for example at departures, check in, security, retail etc., and the reverse for arrivals, including immigration, baggage pickup, retail, arrivals and onwards travel.
Security and immigration processing results in a one-way directional flow and these areas should be designed to accommodate this process. The critical area in the airport terminal is the landside to airside line. The evacuation strategy must accommodate this, and prevent mixing of processed and unprocessed passengers, as well as a major reprocessing of passengers in the event of an evacuation.
The terminal ‘open spaces’ may be subdivided from an evacuation perspective to control safe egress and minimise possible disruption. Where no physical barriers are provided, the strategy may rely on active smoke control systems and fire hazard and control strategies within the fire safety design. A full understanding of the airport fire load should be well understood and defined to ensure appropriate fire safety systems are incorporated into the design.
A key area of an airport terminal that requires special consideration is the baggage handling area. This process should consider the passage of luggage being sent to the aircraft from check-in areas or the receipt from the aircraft and subsequent dispatch to the baggage reclaim carousels. Challenges generally encountered in this area include: maintaining compartmentation between the handling hall and other parts of the terminal, appropriate means of escape signage in a highly complex environment, and ensuring acceptable travel distances for the trained staff occupying the space(s).
The flexibility of retail requirements should be fully considered as this is a key revenue stream for the terminal operators. Hence the need for engaging relevant retail stakeholders in the QDR team.
Fire loads and credible fire scenario’s need to be considered and agreed during the QDR as these will influence many of the fire protection systems required. Unrealistic fuel loads and controls contained within a fire strategy will cause design and implementation problems, resulting in an unrealistic approach as a design basis for fire systems.