Page 74 - Build 161

Fire safety
B-RISK update
Check out the latest news on B-RISK, an invaluable BRANZ tool for re safety engineers.
BY COLLEEN WADE, BRANZ SENIOR FIRE RESEARCH SCIENTIST
FIRE SAFETY engineering describes a process to design re-safe buildings. Design features and safety systems included in a building work together to make a building safe. The longer the distance a person needs to walk to reach a re exit, for example, the longer they will potentially be subjected to smoke and heat from a re.
Calculating evacuation time
In a performance-based design, the time to evacuate will be calculated and compared to calculations of the re growth and spread. The engineer must demonstrate that occupants have enough time to escape from the building before the heat and smoke conditions become life-threatening.
Developed by BRANZ, B-RISK is a re design and analysis software application. Fire engineers can use it to predict re and smoke spread in buildings and to determine how quickly the occupants must be able to leave so they stay safe. B-RISK is used by most New Zealand re safety engineers for re safety analysis.
Used to achieve Code compliance
To meet the protection from re objectives of the Building Code, it must be shown that occupants of a building can safely escape during a re. Buildings also need to allow relatively safe re- ghting and rescue operations and ensure the re won’t unduly a ect neighbouring property and impact the environment.
Simple buildings can be designed using the Acceptable Solutions, but for more complex buildings, a re engineer may need to carry out a performance-based design. This can be done in accordance with the Building Code Veri cation Method C/VM2, or as an Alternative Solution.
The Veri cation Method stipulates various design re scenarios that must be checked, along with what assumptions and calculation inputs to use. The engineer is required to anticipate where res might occur in the building and then determine what the likely impact would be on the safety of occupants.
B-RISK reduces potential for errors
The B-RISK software has been provided with an optional operating mode, assisting users to select inputs consistent with the requirements of C/VM2. This saves time for the user and reduces the potential for user error when choosing the appropriate inputs.
Calculations of visibility through smoke, carbon monoxide concentra- tions and smoke temperatures are made by B-RISK, taking the size of the design re, building geometry and ventilation conditions into account. For example, Figure 1 shows the temperature of the hot gases in a smoke layer in di erent rooms in a building and how it changes over time.
3D graphics display smoke spread
B-RISK uses clever 3D-graphics software called Smokeview devel- oped by the National Institute of Standards and Technology in
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FEATURE SECTION