Flame Spread Index: Comments on the Scale in ASTM E-84T

Publisher’s version / Version de l'éditeur:

Technical Note (National Research Council of Canada. Division of Building Research), 1959-07-01

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.

https://nrc-publications.canada.ca/eng/copyright

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la

première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.

Questions? Contact the NRC Publications Archive team at

PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.

NRC Publications Archive

Archives des publications du CNRC

For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.

https://doi.org/10.4224/20338492

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

Flame Spread Index: Comments on the Scale in ASTM E-84T

Williams-Leir, G.

https://publications-cnrc.canada.ca/fra/droits

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

NRC Publications Record / Notice d'Archives des publications de CNRC: https://nrc-publications.canada.ca/eng/view/object/?id=da6a48e5-a8d2-49cc-a169-97282f0420f2 https://publications-cnrc.canada.ca/fra/voir/objet/?id=da6a48e5-a8d2-49cc-a169-97282f0420f2

'f

ECIHI

Ii

lI<CAlL

NOT FOR PUBLICATION

NOTJE

ｾｉ

FOR INTERNAL USE

PREPARED BY Go Williams-Leir CHECKED BY GWS APPROVED BY NBH PREPARED FOR Subcommittee on Flame Spread of the M!.!.. JulTfl959

CSA Committee on Fire Testso SUBJECT

FLAME SPREAD INDEX

Comments on the Scale in ASTM E-84T.

An anomaly has been pointed out in the rules by which the flame spread index is calculated from the results of the

"Tunnel Test"o This note explains the anomaly and puts forward

some suggested remedies for discussion.

It is presupposed that the reader is familiar with the

general character of the test o However, this is described in

Underwriters' Laboratories of Canada's "Standard Test Method for Fire Hazard Classification of Building Materials" (Subject C-723, July 1956)0

The test-piece used is 24 feet long and an igniting

gas-flame is applied to one end of it; this gas-flame is Ｔｾ feet long if

the test-piece is incombustible. If the test-piece is combustible,

the flame may extend up to a possible maximum of ＱＹｾ feet in the

10 minutes that the test continues. This distance may be called

the "extreme flame travel", whether or not the flame recedes from

this before the termination of the testo If the test-piece is

comb¥stible enough that extreme flame travel reaches ＱＹｾ feet

before 10 minutes, the time it takes to do so may be called the

Ｂｴｩｭｾ to end of tunnel"o .

Thus every material tested should have either a "time to

end of tunneltt _{less than 10 minutes or an Itextreme flame travel"}

less than ＱＹｾ feet, except for the one special case where both

these limits are attained simultaneously.

Having determined the time to end of tunnel or the extreme flame spread, it was thought desirable by those who

originally developed the test to express the results by means of a single index so calculated that for one specified test material the index would be zero, and for another, 100.

Certain rules were devised by Underwriters' Laboratories

2

-Rule 10 When the time to end of tunnel is Ｕｾ minutes or less, the

index shall be 550 divided by the time to end of tunnel in minutes.

Rule 20 When the extreme flame travel is ＱＹｾ feet or less, the

index shall be 100/1905, or 5013, times the extreme flame travel in feet.

These are not the only rules that could have been prepared to satisfy the requirements above; others will be suggested below.

Meanwhile, however, it has been pointed out that there can be materials which would fall in a region between those

governed by Rules 1 and 2, ioeo, materials for which extreme flame

travel reaches the end of the tunnel after Ｕｾ minutes but before

10 minutes. This is admittedly a limited class of materials, but

it should be provided for if only for the sake of logical

complete-nesso To provide for such materials, there are various

alterna-t i ve s, e. go,

Rule

3.

but less than 10 minutes, the index shall be 100.

Rule 4"

but less quotient

the range.This rule conceals all_distinction between materials inAnother possibilityois:.J' .

When the time to end of tunnel is greater than

5t

then 10 minutes, the index shall be the sum of 50 and the

of 275 divided by the time to end of tunnel in ｭｩｮｵｾ･ｳＮ

I - 275

- -r

Rule 3 is equivalent to what is understood to have been

the practice at Underwriters' Laboratories. Rule 4 is equivalent

to the rule contained in a recent proposal to the ASTM.

There is a serious objection to Rule

4

in indices from 77.5 to 100 for materials which are all inferior (i"e. permit more rapid flame spread) to the materials rated under

Rule 2 with indices up to 100. Thus two materials of appreciably

different flame spread hazard could both obtain the same rating of, say, 80 according to whether this rating was attained under Rule 2

or Rule

4.

Inconsistencies like this are liable to arise where

different rules govern in a series of different regions. The aim

In this situation various courses of action are possible. Either the scheme of the Underwriters' Laboratories (Rules 1, 2

and 3) can be retained or the ASTM one (Rules 1, 2 and 4) adopted,

or an alternative course that avoids their faults should be

devised. Some examples of possible alternatives, or "remedies",

are listed below.

Alternative possible courses

Remedy 10 Observe the distance of extreme flame travel up to time

Ｕｾ minutes and take no account of spread after that. Then Rules 1

and 2 are consistent and cover all cases.

Disadvantages.- Presumably the test has hitherto been continued to 10 minutes because useful information was

gained in the last Ｔｾ minutes of test; any such information

would be lost under Remedy 1.

Remedy 2. Adopt Rules 1 and 4 and the following:

Rule 5 When the extreme flame travel is 19t feet or less,

the index shall be four times the extreme flame travel in feet.

Disadvantages.- This system necessitates three rules,

including the more complicated Rule 4. There is still an

overlap of scales but it is now qUite negligible; e.g. a material that spreads flame to the end in just 10 minutes,

which would be rated

77.5

78

5.

Remedy

3.

Rule 6 When the time to end of tunnel is more than 5t

minutes, add 10 to the extreme flame travel in feet, subtract the time to end of tunnel in minutes (or 10 if flame does not reach the end of the tunnel in 10 minutes), and multiply

by

4

Adopting the notation:

x = _{extreme flame travel in feet}

t = _{time to end of tunnel in minutes, or 10 if}

flame fails to reach the end in 10 minutes.

T = _{flame spread index}

Rule 6 may then be expressed algebraically as follows:

When t

»

=

Disadvantageso- There are still two rules and some may find

4

-Remedy 4 demands only one rule to cover all cases:

Rule 7

I

_28.2

(550/19.5

=

28.2)

Disadvantages.- This rule is perhaps too generous to materials a little better than red oak, at least by comparison with

ratings on the system hitherto in use (see examples in Table

I).

Remedy 5 also needs only one rule:

Rule 8

I

=

53.1

(100 v!5.5/l9.5

=

53.1)

Disadvantages.- This rule is too generous to materials worse than red oak, by comparison with ratings on the system

hitherto in use. Examples

Table I gives the ratings for a range of hypothetical cases as calculated by the established rule of Underwriters'

Laboratories, by the ASTM proposal, and by the various "remedies" listed above.

Recommendation

The writer's order of preference among these alternatives would be:

First: Remedies

3,

Second: Remedy 2

Third: Present U.L. practice

Fourth: Remedy 1

•

TABLE I

EXAMPLES OF THE EFFECT OF THE PROPOSED REMEDIES

observations Index computed according to:

Remedy number

U.L. ASTM

1 2 3 4 5

x t

(Rules 1, (Rules 1, Rules 1 Rules 1, Rules 1 Rule 7 RUle 8

(feet) (minutes) 2, and 3) 2, and 4) and 2 4, and 5 and 6

19.5 2 275 275 275 275 275 275 166 19.5 5.5 100 100 100 100 100 100 100 19.5 8 100 84

_'*

I

_'*

_'*

_*

a

a

a

a

ｾｾ Examples cannot be given for this case without knowing experimentally what would

be the extreme flame travel at Ｕｾ minutes.