Application of Fire and Smoke Modelling to Automatic Fire Detection

Application of Fire and Smoke
Modelling to Automatic Fire
Detection
Presented to:
2013 CFAA British Columbia Technical
Seminar
Presented by:
Andrew Coles
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Presentation Overview
› Introduction – Sereca Fire Consulting
› Fire alarm system requirements and design standards
› Location and spacing requirements for heat and smoke
detectors: ‘ordinary’ spaces
› Limitations of prescriptive requirements for non-’ordinary’
spaces
– High atriums, interconnected floor spaces, high bay industrial facilities
› Application of fire modelling
– Understanding smoke and heat detection in non-ordinary spaces
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Objective
› Provide you information about tools and methods available
in the industry
› What Fire Engineering can do to provide cost effective,
functional designs
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Our Company
› Established in Vancouver in 2003 as a Forensic Investigation
Firm
› Offices in Singapore (2008), Calgary (2009), Toronto (2011)
› Building & Fire Code Analysis
› Fire Protection Engineering Design
› Fire Modeling & Visualization
› Evacuation Modeling
› Product Testing & Development
› Fire Investigation
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Fire Alarm System Requirements
› Fire alarm systems may be required by:
– Building Code
– Insurer
– Owner’s risk management
› Building Codes specify design standards:
– Canada: CAN/ULC-S524 Installation of Fire Alarm
Systems
– US: NFPA 72 National Fire Alarm and Signaling Code
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Heat and Smoke Detectors
› In normal buildings and indoor spaces, design standards
recognize spot-type heat and smoke detectors where
automatic fire (heat or smoke) detection is required
› Design standards provide prescriptive rules for location and
spacing, rules of standards apply within limits:
S524
NFPA 72
Heat Detectors
Ceilings up to 9000 mm (29.5 ft) high
Ceilings up to 30 ft high
Smoke Detectors
Ceilings up to 3600 mm (11.8 ft) high "Ordinary indoor locations" (17.7.1.4)
› Essentially equivalent if a 3600 mm (11.8 ft) ceiling is
considered the limit of “ordinary”
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Detector Listings
› Detectors are required to be tested and ‘listed’ by a
recognized laboratory (ie: ULC)
› Heat detectors: listed with a specified maximum rated
spacing (often 50 ft)
› Smoke detectors: listed, but do not have a rated
spacing
– Nominal spacing of 30 ft is assumed, adjusted in
accordance with conditions
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Differences in Detector Listings
› Heat and smoke detectors are listed differently
because heat and smoke behave different
– Heat: easily generated and measured, permitting
repeatable tests
– Smoke: differs in particle size, chemical
composition, and colour depending on fuel,
temperatures, availability of oxygen, ambient
conditions
› Smoke travel paths within a space can be more
difficult to predict than heat transfer
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Prescriptive Requirements Revisited
› Prescriptive rules for smoke detection in S524 and NFPA
72 apply to ‘ordinary’ spaces
› Requirements start with listed/nominal spacing, and
then adjust for:
– Ceiling height
– Ceiling construction: smooth, joists, beams
– Ceiling slope
› Within their limits, prescriptive requirements have been
found to produce acceptable levels of protection
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Application in Modern Buildings
› Many modern buildings contain spaces that are outside of
the ‘ordinary’ category (high atriums, interconnected floor
areas, high ceiling bays)
S524: 5.7.4.2.1 – Note: Data is not available for ceilings higher than
9000mm, therefore, in such installations, fire type, growth rate,
engineering judgment, and manufacturer’s recommendations should
be used. For additional information refer to NFPA 72 …
S524: 5.7.5.1.2 – On ceilings above 3600 mm in room height, spot-type
smoke detector spacing shall be based on fire type, growth rate,
engineering judgment, and manufacturer’s recommendations.
NFPA 72: Requires “performance-based” design for any condition not
included in the prescriptive rules.
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Prescriptive vs. Performance Based
Code or Standard
Objectives and Functional Statements
Prescriptive
•
•
Objectives met by
following exactly what
Code/Standard tells
you to do
Application may not
be directly or
sufficiently addressed
by the Code
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Performance-based
•
•
Toronto
Prove that what is being
evaluated meets the
Objectives of the Code
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Quantifying Fire Effects in Non-‘Ordinary’ Spaces
› ‘Engineering Judgment’ and ‘Performance-based’ design:
requires understanding of the movement of smoke and heat
› Some methods for evaluating smoke and heat movement
include:
– Hand calculations/correlations
– Zone models
– 3D Computational Fluid Dynamics (CFD)
› Methods that are applicable depend on the complexity,
desired resolution of data, engineer’s
knowledge/experience, …
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Analysis Tools
› Hand Calculations (NFPA)
› Zone Fire Modelling: CFAST
› Contaminant Transport (multi-zone):
CONTAM
› Computational Fluid Dynamics: FDS,
OpenFOAM
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Engineering Analysis - Modelling
› For design purposes, the time-dependent movement of
heat and smoke can be evaluated in greatest detail using
CFD
› CFD fire models were originally developed ~ 30 to 40 years
ago as a research tool, and have become mainstream with
increase in computing power
› Validation of CFD models: comparison with measurements
from real-world experiments
› Parametric analysis: evaluation of the effects of various
parameter, such as building ventilation, varying the
ambient conditions, baffles, smoke curtains, etc.
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What is CFD?
› Equations for mass, energy, and momentum are
solved using a numerical grid (mesh)
› Detailed predictions of 3D flow and fire
› Detailed outputs: temperature, smoke, other gases,
velocity
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Fire Modelling Examples
› Examples of ‘non-ordinary’ spaces relevant to
understanding applications of detection spacing and
location
› Atrium spill plume
– 1 MW desk fire
– 6 m (19.7 ft), 12 m (39.4 ft), 18 m (59 ft) height
› Industrial room with roof beams,
– 230 KW transformer oil fire
– 200 mm and 600 mm ceiling beam height
› High bay with sloped roof
– 1 MW wood fire
– Two ceiling beam orientations
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Atrium Examples
› Examining temperature and smoke distribution from a
desk fire into an adjacent atrium space
› Atrium area: 9 m x 30 m
18 m height
12 m height
6 m height
Fire Location
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Atrium – 18 m height (20 x normal speed)
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Atrium – 12 m height (20 x normal speed)
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Atrium – 6 m height (20 x normal speed)
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Atrium - Results
› As height increases there is more smoke compared to heat
at the top of the atrium
– This is why sprinklers are ineffective in high ceiling
spaces
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Beam Ceiling Examples
› Evaluating the movement of smoke and height at ceiling
level in the presence of large beams
› Room dimensions: 15 m x 30 m x 4.6 m
200 mm beam depth
600 mm beam depth
Fire Location
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200 mm Beam Depth (20 x normal speed)
Plan view
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600 mm Beam Depth (20 x normal speed)
Plan view
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Beam Ceiling - Results
› Deep beams – dominant smoke and heat spread laterally
within beam pockets
› Temperature differences between adjacent beam pockets
can be significant
› Smoke dispersion is much less affected by beams
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High Bay with Sloped Roof
› Movement of smoke and heat along a sloped ceiling
with two orientations of roof beams
› Compartment dimensions: 16 m x 30 m x 12 m (peak)
Perpendicular Beams
Parallel Beams
Fire Location
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Sloped Roof – Parallel Beams (20 x normal speed)
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Sloped Roof – Perpendicular Beams (20 x normal speed)
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Sloped Roof - Results
› Initial smoke spread is greatly affected by beam
orientation
› Heat dispersion is less impacted relative to smoke
movement
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Gas Detection
› Simple industrial building with equipment
– H2S leak: with and without exterior wind
– Natural gas leak: with and without building ventilation
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H2S Leak – No wind (20x speed)
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H2S Leak – Wind (20x speed)
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Natural Gas Leak – No ventilation (20x speed)
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Natural Gas Leak – 2 fans on left wall (20x speed)
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Conclusions
› Standards (ULC and NFPA) provide acceptable life
safety requirements within the prescribed limits
› In reality, non-‘ordinary’ spaces require further
consideration
› Smoke and heat movement are not the same for a
specific space and require careful consideration when
designing appropriate detection systems
› Other alternative scientifically-based approaches exist
to design or evaluate detection systems
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Thank you!
Questions?
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