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5th International Tall Building Fire safety Conference 19 June 2018 Single Point of Failure and Inter-relationship between Stair Pressurisation System and Evacuation Strategy for Tall Buildings

M.C. Hui (CEng, CPEng, FIFireE, MSFPE, MIEAust) Fire Engineering Manager BCA Logic Pty Ltd

Making Buildings Safe

WHY DO WE NEED TO PROVIDE A SMOKE EXHAUST SYSTEM? Contents

Overview of occupant fire safety strategy

Review egress provisions for buildings

Single point of failure in egress system and protection options

Pressurisation of escape stairs

Inter-relationship between stair pressurisation and egress strategy

Conclusions

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WHY DO WE NEED TO PROVIDE A SMOKE EXHAUST SYSTEM?

Occupant Fire Safety Strategy

Our homes are our castles 3 of 21



Provision of Exits

Minimum number of exits (Hagiwara and Tanaka, 4th IAFSS Proceedings, pp. 633-644, 1994)

USA International Building Code 2009 4 of 21



Provision of Multiple Exits – Why?

• Provide redundancy – if one exit becomes unavailable, then there is an alternative exit.

• Reduce queuing time when there is a large population on the floor.

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Provision of Multiple Exits – The Inevitable Layout

The two stair entries are at 4.3m to 5.8m apart

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Distance Between Alternative Exits

Building Code of Australia (Class 2 to Class 9 Buildings) 2016 edition

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Distance Between Alternative Exits

Approved Document B (Buildings other than Dwellinghouses) 2006 edition

including 2010 & 2013 amendments

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The Blind Spot (Single Point of Failure)

When the common corridor is significantly smoke logged, no occupants can reach the exit stairs

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Options to Protect The Common Corridor

• Self-closing fire doors for the ‘units’

• Self-closing fire doors for the ‘units’ complete with medium temperature smoke seals and intumescent fire seals

• Ventilating the corridor

• Smoke exhaust system for the corridor

• Pressurise the corridor

• Sub-dividing the corridor by fire door or smoke proof walls does not protect the corridor but discriminates a portion of the occupants on the floor!

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The Escape Stair – Is this the safe haven?

Stair can be non-fire-isolated (Building Code of Australia)

• Connects not more than 3 consecutive storeys in apartment buildings, plus an extra storey if such storey is for car parking or other ancillary purposes

• Connects not more than 2 consecutive storeys in hotels, motels, hostels and the like, plus an extra storey if such storey is for car parking or other ancillary purposes

• Connects not more than 2 consecutive storeys of non-patient care areas in health-care buildings

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The Escape Stair – Is this the safe haven?

Under the BCA, a stair does not need to be pressurised if it does not serve

• any storey above an effective height of 25m

• more than 2 below ground storeys

• an atrium

• a health-care or aged care building with a rise in storeys of not more than 2

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Pressurised Escape Stair

Requirements on pressure within the stair, velocity across the stair entry door, and door opening force vary amongst countries.

The more important issue how many stair entry doors are assumed to be open in the stair pressurisation system design.

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AS/NZS 1668.1:2015 Zone pressurisation dependent system or hot layer smoke control system:

• Fire stair entry door from fire-affected compartment • Main discharge door from fire stair

Air purge system, shutdown system and carpark ventilation system:

• Fire stair entry door from fire-affected compartment • Door immediately above/adjacent to the fire-affected compartment • Main discharge door from fire stair

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BS EN 12101-6:2005 System Examples of use Design conditions

A For means of escape. Defend in place Stair entry door on fire floor

B For means of escape and firefighting (lift shaft also pressurised)

Stair entry door on fire floor and floor above, door to lift lobby, final exit door

C For means of escape by simultaneous evacuation

Stair entry door on fire floor or final exit door

D For means of escape. Sleeping risk Stair entry door on fire floor and final exit door

E For means of escape by phased evacuation

Stair entry door on fire floor and floor above, and final exit door

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NFPA 92 – 2012 and NFPA 101 - 2012 Number of doors assumed to be open is up to the stair pressurisation system designer.

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How does Stair Pressurisation System Work

1.0 m/s

Relief

Building leakage

Ref: John H. Klote, “Smoke Control” in SFPE Handbook of Fire Protection Engineering, 5th edition, Chapter 50, 2016.

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Occupant Evacuation Strategy and its Interrelationship with Stair Pressurisation System

Highrise residential buildings

Potentially long pre-movement times and no particular evacuation pattern

Proulx and Fahy, Fire Safety Science – Proceedings of the 5th International Symposium, pp. 783-794, 1997. 18 of 21



Occupant Evacuation Strategy and its Interrelationship with Stair Pressurisation System

Highrise buildings (other than private residential)

Managed evacuation: Is the evacuation strategy compatible with the stair pressurisation system assumptions?

Particular tenancy Work Health and Safety requirement: The evacuation protocol may pose significant challenges on the stair pressurisation system.

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Conclusions

The path of travel to the fire escape stairs needs to be protected from the effect of fire and smoke to facilitate occupant evacuation, not just the stairs. Stair pressurisation system design must take into account the occupant evacuation strategy implemented for the building which dictates the number of stair entry doors being open at the same time, not just following the national engineering standards.

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QUESTIONS?

THANK YOU FOR NOT FALLING ASLEEP

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