Fire Safety Engineering by David Barber

Does Wood Burn ? The Fire Safety of Solutions in Wood

David Barber

ArupFire Group Leader - Australasia Region

David Barber


Does Wood Burn ?

I have the hardest job - convince the audience that it is ok to have elements within a building that burn, even the structure

Does Wood Burn ?

Wood burns – how it burns is important

Concept 1:Can Fire Performance Be Predicted ?

Concept 1:Can Fire Performance Be Predicted ?

Fire performance of wood has been studied for many years:

1. Research dates back to 13th century

2. Solid wood has highly predictable performance in fire

3. Little variability between countries in species type

4. Knowledge = data = confidence

Concept 2:Not All Wood Is The Same

Concept 2:Not All Wood Is The Same

I

Scale Matters !

Concept 3:How Does Wood Burn ?


Char:

Natural protection for wood

Allows for continued, but diminishing strength during a fire

Well studied and well understood and is predictable

Different wood – different char (due to density and water content)


The importance of char:

Concept 4:Expected Fire Performance


National Construction Code:

Performance Requirement CP 1 -

“A building must have elements which will, to the degree necessary, maintain structural stability during a fire appropriate to.......”

Structural wood needs to provide an equivalent level of performance as concrete or steel


Concrete:

- Inherent protection

In a fire:

- Spalling (>600C)- Exposed steel- Bending- Failure is very rare


Protected Steel:

- Reliant on inherent strength and applied protection

In a fire:

- Will deflect (>550C)- Protection limits heat- Unlikely to collapse- Need replacement


Structural Wood:

- Inherent protection from char

In a fire:

- Will deflect- Unlikely to collapse- Need replacement


Summary:

1. Concrete – fire resistive, elements may need replacement after a major fire

2. Steel – fire resistant with additional protection, will need replacement after a major fire

3. Structural wood - fire resistant, will need replacement after a major fire

Concepts:Summary

Concepts for fire performance of wood:

1. Fire performance is well understood

2. Not all wood is the same - scale matters

3. Solid wood chars – which has predictable performance in fire

4. In a fully developed fire, wood can perform equivalent or better than steel

What Does the NCC Allow for Solutions in Wood ?


Summary of limitations:

1. Type A construction (non-combustible) is required for:• Class 5 (office) – Rise in storeys of 4

or more• Class 2 or 3 (residential) – Rise in

storeys of 3 or more

2. Type A - all elements must be non-combustible (except a mezzanine), hence no wood permitted.......


So, how is wood used in buildings ?

1. NCC allows fire engineering solutions for areas of non-compliance (so called “performance based” approach)

2. Fire engineering solutions will need a good fire engineer, who understands structural wood solutions, understands the process of approval and design implementation

Solutions in Wood - Facades

Solutions in Wood – Facades

Solutions in Wood – Internal Elements

Case Study – 5 Storey Building


1. Could be concrete, steel or solid wood structure

2. NCC - 120 mins FRL to structure, separations

2. Many different fire protection options • Fire rated compartmentation• Smoke detection• Sprinkler protection• Additional stairs


1. Wood structure and steel are very similar from a fire safety view point

2. Using sprinklers with a trade off in fire ratings, reducing to 60 minutes FRL

3. Structural wood was determined as the better option

4. Wood elements can be pre-assembled off site for quicker construction


1. Solid wood structure of columns and beams, inherent FRL with load bearing capacity in excess of 60 mins FRL

2. Wood assumed to not have any plasterboard protection (not required to be maintained)

3. Steel would require protective coating (sprayed or paint) to achieve 60 mins FRL (requiring maintenance)


Designing details

1. Assist with detailing for:• Connections• Floor and structure connections• Edge details

2. Penetrations for building services are complex to solve

3. Facade interface with wood edge beams are problematic


Case study summary:

1. Performance requirements of the NCC can be met using structural wood

2. Designs can gain approval, provided the engineering is substantive

3. Similar approach to any other fire engineered solution

Summary

Wood does burn – but we understand how

Structural wood is equivalent or better than structural steel in many built situations

A lack of understanding of the fire performance of wood by many

Wood can be used, but you need a fire engineering solution


David BarberArupFire Group Leader – Australasia Region

Questions?

Fire Safety Engineering by David Barber

Business

Transcript of Fire Safety Engineering by David Barber