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Fire Resistance Levelsontentse Safety

e Hazard Properties (Specs C1.10 & C1.10a)

.10 Materials & Assemblies

.10a Floor Coveri!s

.10a "all & Ceili! #ii!s

e $esistace #evels%e ood is e'posed to %i!% temperatres it ill decompose to provide a islati! layer 

c%ar t%at retards frt%er de!radatio of t%e ood. %e rate of c%ar is iitially fast bt ase dept% of c%ar icreases* t%e rate of c%ar slos becase of t%e icreasi! islatio

ovided.

e rate at which timber chars varies between species and is predominately dependent on

nsity and moisture content.

e predictability of timber charring is used by building regulators to develop Fire

sistance Levels for building elements like large cross-section timber columns and beams.

e Australian Standard AS !"#.$Timber Structures : Fire-resistance of structural  timber

embers provides a method of calculating fire resistance levels for solid timber.

rge cross-section timber is able to carry load during a fire event as the char occurs on the

tside of the element and the effective cross section of the timber is only slowly reduced.

e insulating %ualities of timber mean that although the temperature at the char layer may

&##o'( the temperature of the inner wood is considerably lower. The remaining uncharred

oss-sectional area of a large wood member remains at a low temperature and can continuecarry a load.

alculating Depth of Char 

e Australian Standard AS !"#.$ Timber Structures : Fire-resistance of structural  timber

embers provides a method of calculating a conservative char depth. )y substituting

propriate values in the e%uations below( the residual cross-section may be calculated with

fficient accuracy for design of the elements and conse%uent compliance with the%uirements of the )'A( as allowed for in Specification A".& 'lause &.

e *otional 'harring Rate is given by

' + #.$ , "#/01"

here

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' + *otional 'harring Rate( in millimetres per minute mm/min1

0 + timber density at a moisture content of "2 in kilograms per cubic metre

kg/m&1

e 3ffective 0epth of 'harring in millimetres1 is given by

dc + 't , !.4

here

dc + calculated 3ffective 0epth of 'harring in millimetres mm1

' + notional charring rate in millimetres per minute mm/min1 as calculated

t + period of time( in minutes min1

ote that the net effect of charring/fire will depend on whether ( "( & or $ faces of theember are e5posed to the fire.

oadly speaking( the charring rate '1 is inversely proportional to the density in kg/m &1 of

e timber element. The calculation of e5pected performance must however allow for

arring and hence reduction in cross section si6e and thus load carrying capacity1 on ( "(or $ sides( as appropriate.

ample of calculating the fire resistance level (FRL) of a structural element

ppose t%at to provide strctral spport der fire coditios a blac+btt timber post is,ired to measre at least -0 ' -0 mm for 0 mites of e'posre to fire. /lac+btt at a

C. of 1 %as a desity of 200+!3m4 so t%e otioal c%arri! rate !ive by t%e e,atiosove old be 0.-mm3mi. %is old reslt i a c%arri! dept% of 45.- mm o eac% side

t%e post.

e size of post re,ired* assmi! t%at t%e fire ill affect all for sides of t%e post* old-0 6 45.- 6 45.- 7 1- ' 1- mm. 8f t%is size is ot available t%e t%e e't largest  size

old be sed.