VERIFICATION OF OMISSION OF FIRE DAMPERS AND/OR SUB … · 2017. 5. 18. · • Sep. smoke exhaust...

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VERIFICATION OF OMISSION OF FIRE DAMPERS AND/OR SUB-DUCTS FOR

CENTRALISED VENTILATION SYSTEMS

Ulf JohanssonSenior Fire EngineerRED Fire Engineers


CONTENTS

• Cost-benefit case study• BCA and AS 1668.1• Alternative design (fans in operation)• Basic principles of smoke spread• Fire induced pressures and flows• Just another purge system?


THREE THINGS TO TAKE HOME

• Are dampers and/or sub-ducts really necessary to prevent smoke spread?

• It is not a “purge system” per se• It’s a lot less expensive


COST-BENEFIT EXAMPLE

• 80 SOUs (e.g. hotel)• Cost savings: over 80 %


BUILDING CODE OF AUSTRALIA

• EP2.2 – Temperature, toxicity and visibility• CP2 & CP8 – Fire spread• CP3 – Smoke and fire spread

(only for Class 9a patient care areas and Class 9c)


BUILDING CODE OF AUSTRALIA

• E2.2 – Ventilation systems:• AS 1668.1 smoke control system, or• Smoke dampers + shutdown

• E2.3 – Special hazards


AS 1668.1-2015

• Section 5 – Miscellaneous systems not smoke control systems• Minor exhaust (<0.1m2): Sub-ducts + fan operating• Major exhaust (>0.1m2): Smoke and fire dampers

Sub-duct (extract from AS 1668.1-2015)


BASIC PRINCIPLES

• Early phase (pressurization, high flows, low temperatures)• Main hazard: Smoke spread

• Late phase (flashover fire, high temperatures, pressure relief)• Main hazard: Fire spread


BASIC PRINC. – EARLY PHASE

• Fire -› temperature increase -› volume expansion -› pressure increase in enclosure -› fire flow into ducts


BASIC PRINCIPLES OF SMOKE SPEAD

• Supply:Pfire > Psupply -› spread

• Exhaust: Pbranch> 0 Pa -› spread


FIRE FLOW – EARLY PHASE

• Fire induced flow calculated as:

𝑞𝑞𝑓𝑓 = 0.28 � 𝑉𝑉𝑒𝑒0.53 � 𝛼𝛼0.425

𝑞𝑞𝑓𝑓 maximum fire induced flow [m3/s]𝑉𝑉𝑒𝑒 enclosure volume [m3]𝛼𝛼 fire growth rate [kW/s2]


FIRE FLOW – EARLY PHASE

Example: 100 m3 room (approx. 40 m2), fast growth rate

𝑞𝑞𝑓𝑓 = 0.28 � 1000.53 � 0.0470.425 = 0.88 𝑚𝑚3/𝑠𝑠


MAX. TEMP. – EARLY PHASE

• Peak temperatures in room less than 340 °C


BASIC PRINC. – LATE PHASE

• Peak fire temperatures of 800 – 1200 °C

• Broken window or other pressure relief (negligible pressure build up in enclosure)


ALTERNATIVE DESIGN USING FANS IN OPERATION

• Sep. smoke exhaust fan or by-pass • Non-combustible ducts• Generally non-combustible grille/diff.• Protection of elec. supply

• Power supply in its own fire compartment (incl. dampers)• Cables/wiring protected


EXAMPLE

• 20 fire compartments á 100 m3

• Only mechanical exhaust, central plant• Flow from each compartment: 50 l/s• Supply via façade (10 Pa pressure drop @ 50 l/s)• Pressure drop from main duct to grille/diffuser: Min. 50 Pa


T ne , 15 0 0 , 2h , - 1 2 4 . 2 , - 0 4 5 : q h T- 1 2 4 . 2 P a

- 1 0 0 0 l / s2 0 . 0 C

: t 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1

5 0 . 0 P a

1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0

3 8 . 7 P a 3 6 . 6 P a 3 7 . 9 P a 4 0 . 1 P a 4 3 . 4 P a 4 8 . 0 P a 5 4 . 0 P a 6 1 . 6 P a 7 0 . 9 P a 8 2 . 0 P a" Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om"

1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1t , 1 0 , 5 0 t , 1 0 , 5 0 t , 1 0 , 5 0 t , 1 0 , 5 0 t , 1 0 , 5 0 t , 1 0 , 5 0 t , 1 0 , 5 0 t , 1 0 , 5 0 t , 1 0 , 5 0 t , 1 0 , 5 0T n T n T n T n T n T n T n T n T n T n

3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1

1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0

3 8 . 7 P a 3 6 . 6 P a 3 7 . 9 P a 4 0 . 1 P a 4 3 . 4 P a 4 8 . 0 P a 5 4 . 0 P a 6 1 . 6 P a 7 0 . 9 P a 8 2 . 0 P a" Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om"


e n d 1 1 s y s t em 1 8 2 e l eme n t s 0 e r r o r s 6 o b s e r v a t i o n s 2 0 1 7 - 0 3 - 2 4 1 8 . 3 3 . 2 5

Fan

-50 Pa


" F i r e "

T , 2 0 , 3 4 0T ne , 1 h ?5 0 0 , 2 6 5 8 . 2 P ah , - 1 2 4 . 2 , - 0 4 5 : q h T q , 0 , 8 8 0

- 4 5 . 0 P a- 8 1 4 . 2 l / s d , 9 9 9 , 0 . 1

8 8 . 2 C: t 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 9 9

- 0 . 2 P a

1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0

9 9 " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om"


3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1 3 1 5 , 0 . 1

1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1 1 6 0 , 0 . 1t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0 t ? - 5 0

" Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om" " Ro om"


e n d 1 1 s y s t em 1 8 6 e l eme n t s 0 e r r o r s 6 o b s e r v a t i o n s 2 0 1 7 - 0 3 - 2 4 1 8 . 3 7 . 0 8

Fire effects

Fire0 Pa

Fan requirements to achieve 0 Pa at branch


EXAMPLE – EARLY PHASE

• Negative pressures will always be maintained in branch between fire compartments because:

-125 Pa @ 1000 l/s > -56 Pa @ 815 l/s

• Smoke spread will not occur in a fire

• Mixing temp at fan, early phase – calculated to 89 °C


EXAMPLE – LATE PHASE

• Assume worst case fire temp 1200 °C

• Mixing temp at fan, late phase (approximate):

𝑇𝑇𝑓𝑓𝑓𝑓𝑓𝑓 =50 � 1473 + 19 � 50 � 293

20 � 50= 79℃


EXAMPLE – CONCLUSION

• No smoke spread can occur if fan operates as per normal

• Fan has to have a temperature rating at least of 90 °C

• No fire or smoke dampers or sub-ducts required


PRO’S AND CON’S

Fans in operation Smoke/fire dampers

Sub-ducts

Pro’s • No sub-ducts or dampers

• Reliable • Less maintenance

• DtS• ”Trusted

design”

• DtS• ”Trusted design”• Low maintenance

Con’s • Requires calculations

• Expensive• Maintenance

• Floor area • Protects against

smoke spread?


JUST ANOTHER PURGE SYSTEM?

• AS 1668.1 allows “purge systems”• Smoke exhaust fan (temp. rated), control of flows in fire mode• Perf. Criteria: Door forces < 110 N



• Purge systems do not guarantee that• the mixing temp at the fan is less than the fan rating• the exhaust fan can prevent smoke spread via the exhaust ducts• the supply fan can prevent smoke spread via the supply ducts



• Same system as in the example but with 10 Pa pressure drop • Pressure in branch + 20 Pa

(smoke spread could occur)


FINAL NOTES

• Method used for over 20 years

• Used in high-risk occupancies, e.g. hospitals


QUESTIONS?

Contact: [email protected]

Thanks for listening!

VERIFICATION OF OMISSION OF FIRE DAMPERS AND/OR SUB … · 2017. 5. 18. · • Sep. smoke exhaust...

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