1. Atrium Fire Protection
VESDA
Atrium Fire Protection

2. Increased use of Atria within buildings
Atria add space and light to facilities
Attractive architectural feature
Useful link to multiple occupancy facilities
Often main escape route
With the advancement of modern building construction, the inclusion of atriums within a building design has become very popular. Atrium design is widely used for example in offices, shopping and convention centres. An atrium provides a focal point of a facility giving a light and airy feel and is often aesthetically attractive (architects and owners don’t want to see feature detracting detectors). It is also a cost effective method of construction and often the main means of escape, consequently early detection is paramount to ensure effective fire response action and safe evacuation.

3. Challenges for Atria Can move buildings outside scope of fire codes
Smoke stratification
Smoke dilution
Solar radiation
Changes in airflow
Maintenance access
Building movement
Environmental obstructions
People gathering, egress issues
Although an atrium provides many advantages, they introduce a host of challenges for effective fire detection. By definition they are more often than not out side the scope of the codes for point detection due to the height.
One of the more major issues of effective detection within atria is smoke stratification. Stratification occurs when the smoke or hot gases flowing from the fire fail to ascend to the smoke detection points mounted at a particular level above the fire due to the loss of buoyancy. This phenomenon has a great impact on the performance of ceiling mounted smoke detection systems as well as other detection technologies such as projected beam detectors. An increase in smoke under the stratification level can impair escape from the atrium.
In conjunction with stratification the fire detection system can also be compromised by dilution. Dilution is common within large open areas and high ceilings and areas that have HVAC systems providing comfort air within the atrium. During the early stages of a fire, smoke is mixed with clean air, which effectively dilutes the amount of smoke that is being generated. Consequently an ever increasing fire load is required before detection is achieved.
Environmental effects such as building movement (caused by building expansion/contraction) can cause beam misalignment. In addition, architectural features can make alignment of beams difficult.
Maintenance is an ongoing issue. Access to ceiling mounted detectors will require specialist lifting equipment or scaffolding to reach detectors, and as facilities become increasingly 24hour operational, there is a need to isolate sections for the maintenance to be safely undertaken.
All in all, an atrium is a complex fire detection environment. The difficult detection conditions, variable environmental issues, and potentially complex maintenance programs make the design of an effective fire detection system a challenge.

4. Potential Scale of Atria
Ceiling height of over 60m
Large open areas exceeding 10,000m2 (110,000ft2)
This slide shows the potential scale of atria. The height can be too high for point detectors.

5. Solar Radiation & Stratification
This clearly shows the effect of stratification. Smoke is levelling out before it reaches ceiling height, with only a small amount actually reaching the ceiling.

6. Environmental Obstructions
Alignment of beam detectors can be problematic in applications where there is no line of sight.

7. Access problems
Complex and high structures require specialist lift or scaffolding to reach detectors. This can lead to very expensive maintenance, or worse still, not being undertaken at all.

8. Design requirements Immunity to
building movement
direct sunlight
false alarms due to site features
Ability to overcome stratification and smoke dilution
No labour intensive maintenance
Multiple alarm outputs for staged warning
Flexible design to provide protection where needed
This lists the atria fire protection design requirements that are commonly specified by architects, consultants, insurance companies, owners and the fire service for effective detection that is reliable and stable.

9. Detection solution comparisons
Point Detectors
Difficult to mount in atria
Effected by stratification
Effected by dilution
Major maintenance issues
High cost of ownership
It is important to consider the various fire detection technologies in order to determine the most effective solution. Point detectors can prove difficult to mount due to the architectural nature of an atrium. This photo illustrates the complexity of situating and mounting ceiling mounted detectors. Not only will the detection performance be ineffective, but it will be very difficult to access and carry out maintenance and repairs.
Stratification is a major issue as stratification along with dilution prevents sufficient smoke reaching the point detectors. The stratification photo illustrates how stratification prevents smoke from reaching point detectors.

10. Detection solution comparisons
Beams
Beams at lower than 600 mm from ceiling level require separation 12.5% of height (BS 5839). Solution becomes very expensive.
False alarms due to building movement & seasonal decorations
Affected by stratification
Affected by dilution
Susceptible to damage from seasonal decorations
Access problems for maintenance
Beam detectors have similar issues with stratification and dilution, even though they can be installed up to 40m in accordance with BS5839. However due to stratification, and the uncertainty of a smoke plume forming, it is often necessary to install beams at a lower level. If this is greater than 600mm below ceiling level, then BS5839 requires the width of the area to be protected on each side of an optical beam to be regarded as 12.5 % of the height above the highest likely seat of the fire. For example, if the chosen beam height is 10m (as shown in BS5839, page 60, Fig 13), each beam would need to be installed at 2.5m spacing, which would result in a totally impractical and very expensive solution.
Building movement and seasonal decorations are also major factors that cause false alarms. The photo shows that decorations and promotional banners are all potential contributors to false alarms.

11. Detector solutions comparison VESDA
Vertically as well as horizontal sampling pipe within architectural structure
Installed at ceiling level or at different heights
Not affected by building movement or seasonal decorations
Overcomes smoke stratification and dilution
System design to accommodate environmental conditions
Low cost of maintenance
By comparison, VESDA overcomes all of the problems associated with point detectors and beams. The detector units can be installed at low levels in service areas for ease of access and maintenance. Remote displays can be situated within control and security areas for early visual indication of a change in status. The pipe work can be hidden within the structure and provide detection vertically as well as horizontally to overcome stratification problems, and where permissible one detector can protect up to 2000sqm (20,000 sqft).
Dilution is not such an issue for VESDA, as VESDA benefits from diffusion. As smoke spreads, more than one sample hole will be exposed to the smoke, and consequently the accumulation of this diffused smoke will improve the detection capability of the VESDA system. The dynamic sensitivity range capability of the VESDA system (0.005 – 20% obscuration per metre), coupled with the design program ASPIRE 2, provides a tailored solution matched to risk. Combined with the four alarm indicators (alert, action, fire 1 and fire 2), VESDA can signal a staged warning as part of the agreed response planning, from early warning up to meeting the fire load test criteria as stipulated by the design consultant.
BS5839 gives recommendations for height limitations with Aspirating Smoke Detectors. However BS5839 L5 gives recommendations to the specific fire safety objective that is part of the fire risk assessment or forms part of the fire engineering solution. Vision Systems can show considerable experience in this area through its Application Engineering Group. This group uses combined modelling and verification techniques to provide performance based design supported by actual installations within complex applications such as atria.

12. Detector solutions comparison VESDA
Sampling pipes can be installed along:
- structural beams
vertical air handling columns
roof structure
the wall cavity (concealed)
vertical advertisement columns
This illustrates how VESDA pipe work can be integrated within the building structure to provide discrete detection. The detector unit can be installed in an accessible secure area to minimise the need for disruption within the protected area during maintenance.

13. Recap Atria increasing feature of modern buildings
Complex environmental situations
Standard methods of detection don’t work well
Stable detection with ease of maintenance required
Multiple alarm settings for early fire detection as well as orderly evacuation to minimise business interruption

14. Case Study Gaylord Texan Resort & Convention Centre, USA
VESDA
Case Study
Gaylord Texan Resort &
Convention Centre, USA
As an example where performance based design was critical. The following is an illustration of how VESDA overcame a difficult detection environment within the Gaylord resort.

15. Gaylord Texan Resort & Convention Centre
In this application, the fire hazard is the normal day to day activities such as food preparation, electrical malfunction, plant malfunction and general occupancy related issues such as discarded cigarettes. A total of 6 VESDA LaserPLUS detectors are installed to protect the Atrium. The Atrium area alone covers 8,100 sq.m (87,000 sq ft)

16. Building Description
1511 guest rooms, more than 37,180 m2 (400,000ft2) of pre-function, meeting and exhibition space
Atrium with a 64m (210ft) high glass domed ceiling. The size of the atrium area alone is approximately 8,100 m2 (87,000 ft2)
Four cupola exhaust fans installed on the ceiling structure with a total ventilation capacity of nearly 100 m3/s (3,500 ft3/s), approx 60 (2,100) to 70 m3/s (2,500 ft3/s) of fresh air is supplied into the atrium.
The Gaylord Texan Resort is a major facility, not just a complex structure but also a difficult environment to detect fire due to its significant physical size and constantly changing environment through the air conditioning system. Added to this is the fluctuations in outside temperature that can produce massive internal temperature differentiation within the atrium. In summer, the outdoor temperature can exceed 40 deg C (104 deg F). With the glass roof structure, the temperature at the ceiling level will typically be 20 deg C (68 deg F) higher than the ground temperature. How will the temperature gradient affect the smoke propagation? Will the stratification layer form, and at what height?

17. Project Considerations
Attributes
Performance Based Design
Smoke Control, Detection & Tenability
Designed to meet performance requirements in terms of size and type of fires, detection response time for 5 MW fire (peak) within 5 minutes from fire start
Technology Fit
VESDA air sampling system was assessed in direct comparison with other technologies such as beam detectors
Unique Architecture
Considered stratification, structure, fire locations, HVAC operation, etc.
Innovation
Aesthetics, VESDA provides unobtrusive detection, easy maintenance
Performance Assessment
Successful in-situ smoke tests to verify designs and prove fire modelling.
In addition to the extreme environmental conditions, there are many areas associated with large open area protection that are not covered by prescriptive codes. Therefore Performance-Based Design is the only solution.
VESDA met the performance based design requirements of the project, meeting the fire load requirements as required by the consultant as well as the interfacing into the cause and effect matrix of local indication, fire alarm panel connection, and interfacing to the smoke extraction system.
In prescriptive codes, “Technology Fit” is generally not a concern, but in this application, it was critical to select an appropriate technology to ensure that the fire protection system was not compromised.

18. Benefit of computer aided modelling
System can be modelled with fire in various locations
System can be modelled with a range of fuel types with different fire characteristics
Results can be verified with actual smoke tests in accordance with acceptable test methods
Impact from environmental conditions can be evaluated
Airflow characteristics can be modelled to ensure an optimal placement of detection points
System performance can be quantitatively assessed to meet design criteria
According to building codes and common practice, a ‘fast growth 5 to 10MW fire’ is used in such an environment to activate the building’s smoke management and evacuation system. The fire detection system must respond within 5 minutes from the start of the fire. The specified fire load is very large and not practical to generate in real life. As a result the first challenge was to computer model the various scenario's using fire modelling software. To simulate the likely stratification issues, the model catered for floor to ceiling temperature differences from 20 to 60 deg C (68 to 140 deg F), as well as variable fire locations, fuel loads and types.

19. VESDA Design Alarm Functions Pipe work
Alert: Supervisory signal in the fire panel, investigation
Action: Actuates the smoke control process
Fire 1: Activates the building fire alarm system through the fire panel
Fire 2: Evacuation
The fire code requires fire signalling and smoke evacuation control from the activation of the smoke detection system. The VESDA system was designed to satisfy building and life protection requirements. As VESDA has multiple alarm outputs, the product was also able to provide additional interfacing to assist with a planned cause and effect strategy that gives early warning and action to reduce damage and provide more effective evacuation.
Pipe work
32 sampling holes per VESDA zone
Placed m (105ft – 197ft) above floor in atrium

20. Performance: Modelling
Environmental conditions
Detection requirements
Technology used
Different fire scenarios
Detection within 5 mins
5 MW fire, 45 to 60 °C, 34m to 60m
(113 to 140 °F, 112ft to 197ft)
A large number of simulations were undertaken with a range of fire loads and materials from liquid pool fires, standard sofa fires and timber fires. Ventilation and ambient temperatures were also varied as was the location of fires within the atrium. The project required the detection of smoke from a 5 MW fire within 5 minutes of ignition.
Vision Systems modelled the specified 5MW fire, as well as a significantly smaller fire load (500KW). The two fire model videos show the difference in stratification and smoke plume between the two simulated scenarios. (Press the red button(s) and acknowledge the Windows message to play each video clip)
In the video clips:
black represents smoke levels of approx 0.1 to 0.2% obscuration/m,
green represents approx 8% obscuration/m,
red (peak) represents 14% obscuration/m.
The videos show that smoke stratified at different heights with vastly different characteristics. This presents a huge challenge to beam type detectors because unless they are mounted at different heights (in line with the stratification layer) and closely spaced, they may not be able to detect fires efficiently.
In contrast, while there are smoke layers forming at different levels, the models showed that a percentage of the smoke always reached the ceiling due to smoke buoyancy. Because of VESDA’s early warning capability, this small amount of smoke was sufficient to trigger alarms.
500 KW fire, 25 to 40°C, 34m to 60m
(77 to 104°F, 112ft to 197ft)

21. Modelling Results
VESDA detected smoke in all simulated stratification conditions within 5 minutes from ignition of a 5 MW fire
In fact, much smaller fires (0.5MW) were detected within the required detection time of 5 minutes
Even though the project requirements specified detection of a 5MW fire within 5 minutes, Vision Systems was able to model the effect of a significantly smaller fire load (peaked at 500KW) to illustrate that VESDA could give much earlier warning and effective control.
The model showed that the VESDA design could detect a much smaller fire of 500KW in 5 minutes.

22. CSIRO developed test
Test method as developed by CSIRO, suitable for the assessment of Early Warning Detection Systems in large open spaces
The test method was designed in conjunction with CSIRO and consisted of 4 to 6 radiant heaters as well as a smoke cartridge to represent a fire size in the order of 25 KW at the start of the fire. The smoke test set up was positioned in the centre of the atrium (under VESDA fire zone 7, see later slide). Fire tests were conducted by local fire contractors witnessed by fire consultants, construction engineers, the building owner representative and AHJ’s.
The total heat generated from the radiant heaters was equivalent to a fast growth fire of approx 230KW if the activation time is 3 minutes.

23. CSIRO developed test
Test underway

24. Performance: In-situ Tests
Fire started at centre of atrium (under Zone 7)
Detection Time < 5 minutes
Although the test was undertaken in the centre of the atrium it can be seen that detection occurred in all 6 zones. Therefore there must have been a wide diffusion of smoke within the atrium.
Fire 1 was reached well within the 5 minute limit with the first alert at just over 3 minutes. It was achieved with a fire size of approximately 230KW, far smaller than specified. Both the time to detection and fire size specifications were far exceeded.
By setting all four alarm levels correctly, the VESDA system can be designed to provide an early warning (for investigation) and continue to fire detection at a later stage (for evacuation).

25. Performance test across zones
The VESDA event log clearly shows the time when smoke obscuration peaked within each zone. This function would also be used in ‘auto learn’ to establish the ambient background levels within the protected area, thereby allowing the VESDA alarm levels to be set appropriately above the standard environmental conditions. VESDA provides both an early warning system and very stable fire detection system for a large open area.

26. Technology comparison
KPIs
VESDA
Beam Detector
Early Fire Detection
Yes No
Affected by smoke stratification layers
Staged alarms for good emergency response plan
False alarms due to movement of building structure
Affected by sunlight (Glass domed ceiling)
False alarms due to dust contamination
False alarms due to obstruction of beam path
Access for maintenance and testing
Easy
Difficult and costly
Aesthetics
Unobtrusive
Devices highly visible
Cost of total system ownership
Lower
Higher
It would not have been possible to install point detectors within this grand atrium – they simply would not have met the performance criteria, and would have been impossible to maintain. This table highlights the advantages of VESDA against the only other considered detection method, which is beam technology. VESDA clearly provides the best solution in this application.
Note that when beam detectors are installed in accordance with BS5839 (2002 Edition), the upfront cost and the on-going maintenance costs increase significantly because of the high number of beam detectors required. In addition, the closer spacing requirement at the lower level may be impractical due to the interior building features and activities.

27. Conclusion
VESDA successfully provided early fire detection in this grand atrium
Performance Based Design methodology was applied to meet the fire safety system design requirements
Computer modelling proved the system design in a difficult environment of high airflows, and where the effects of stratification were highly variable
In-situ smoke tests confirmed the accuracy of the VESDA modelling