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Technical Note (National Research Council of Canada. Division of Building Research), 1973-05-01
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Fire Hazard Tests of Translucent Lighting Panels
McGuire, J. H.
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https://nrc-publications.canada.ca/eng/view/object/?id=97832fae-035c-4869-9bdb-569edfb26aa1 https://publications-cnrc.canada.ca/fra/voir/objet/?id=97832fae-035c-4869-9bdb-569edfb26aa1
DIVISION OF BUILDING RESEARCH
NATIONAL RESEARCH COUNCIL OF CANADA
••
'f
EClHIN lICAlL
NOTE
No.
572
PREPARED BY J.H. CHECKED BY G. W. S. APPROVED BY
A.G.W.
PREPARED FORｾ May 1973 Associate Committee on the National Building Code
SUBJECT FIRE HAZARD TESTS .OF TRANSLUCENT LIGHTING PANELS
In general, the flammability of wall and ceiling linings of enclosure s will sharply influence the development time and likelihood of. fire, unle s s unusual circumstances prevail such as a heavy loading of highly flammable contents. Regulation of lining flammability appears to be a very effective means of reducing hazard, and for ceiling and wall1ining materials the ASTM E84 (CSA B54. 2) test is usually accepted. as the most appropriate method of comparing flarnmability of different material assemblies.
In discussing translucent lighting panels the National Building Code invokes the ASTM E84 (CSA B54. 2) test, which in turn requires that test specimens that might fall or melt away from the ceiling mounting
shall be supported by wire mesh and metal rods. Tested in this manner, most lighting panels on the North American market give very high flarne
spread ratings that fail to meet the NBC requirements.
The object of the investigation noW reported was to determine
whether the fact that most plastic lighting panels fall from their mountings as temperature s rise could be utilized to frame possible Code require-ments that would continue to control fire hazard but be less onerous than those of the 1970 NBC.
A number of North American code s completely eliminate flarne-spread requirements for lighting panels, provided they will fall from their mountings at a temperature 200 F deg lower than their ignition temperature. De spite the wide spread acceptance of this criterion, its practical significance is lirn.ited because conditions following the outbreak of a fire are transient and not steady-state. At anyone time, therefore,
.,
-z-a spectrum of tem.per-z-atures exists throughout -z-a pl-z-astic diffuser; it is not one uniform tem.perature throughout. Certain structurally essential portions m.ay well be at a low temperature whilst other regions are actually ignited. In absolute terms the criterion thus has little m.eaning.
PRELIMINARY TESTING
Any test developed to assess the hazard of plastic lighting panels needs to relate to all m.anner of assem.bly and fire conditions. It was therefore decided that, in order to represent highly adverse conditions, test specimens should be directly exposed to flam.e originating at the
start of a te st. Such a condition m.ight apply, for exam.ple, as the re suIt of ignition of leaking gas or flammable liquid.
As an exposing burner, two 3/8-in. orifices 3
liz
in. apart were utilised; they were located 2 3/4 in. below the edge of the first lens and projected upwards at an angle of 30 degrees. Natural gas (calorific value approximately 1,000 Btulcu ft) was supplied at arate of 1/3 cu ft/m.in to give a diffusion flame that enveloped the whole 2-ft width of the te st specimen for a distance of a1m.ost 2 ft.
The first test involved a 2-ft sq ribbed acrylic lens supported at two edge s and inadvertently m.ounted upside down. A second specimen was m.ounted beyond and abutting the first to discover whether it would ignite from. the first. Sheets of asbestos surrounded the test specimens to represent a substantially plane ceiling.
Within 1 m.in of ignition of the gas, ·the leading edge of the first specimen had ignited and flaming droplets were falling to the floor beneath (9 ft below). Before 2 m.in had elapsed the flam.ing droplets were rem.aining alight on reaching the floor. Shortly after the 2-m.in period the exposing gas flame no longer impinged on the test specimen because the leading edge had ITlelted away and was hanging down to som.e extent. The gas flame continued to burn above the burner ports. but it no longer heated the test speciITlen substantially.
These conditions prevailed for nearly 35 m.in. The first lens burned slowly and steadily and flam.ing ITlolten drops froITl it contribut ed to a fire on the floor. Finally, this lens fell without igniting or in any way dam.aging its neighbour. During the test the lighting panels constituted the only ceiling, so that after 2 1/4 ITlin, following the de struction of
the first few inches of the test specimen, the exposing gas flame was vented to a free atmosphere.
-3-To give more likelihood of rapid flame propagation, a ceiling was mounted 11 in. above the false ceiling composed of test specimens and asbestos sheets. The complete assembly was 8 ft long and the ends were open; the width was 4 ft and the sides were closed. A test was carried out under these conditions, using the same type of specimen as previously. Behaviour proved to be substantially the same, except that the time scale was slightly shortened, the first section falling out
after 28 1/2 min.
A third test was carried out using a plane 2- by 4-ft lens. Again, the exposing flame was vented to the ceiling void early in the test (about
1
liz
min). In this case the first specimen did not have the opportunity to fall out because the flame front extinguished itself 4 min 10 sec after the start of the te st.From these tests it was inferred that exposure under the chosen conditions could give ignition of many types of plastic lens prior to their dropping out. No great hazard of rapidly developing fire appeared to be created,however, and it was thought that other conditions should be investigated in this context. The principal negative performance feature thus far brought to light by the te sts was the ability of the panels to
create flaming droplets which formed a pool fire on reaching the floor. The hazard inherent in this phenomenon is difficult to assess, bearing in mind the fact that it will only prevail when a substantial fire exposes the ce iling .
E84 "DROP-OUT" EXPERIMENTS
The hazard to be investigated is that of rapid propagation of fire along a ceiling, precisely the context of the ASTM E84 test. The necessary conditions of draft, heat conservation, etc., conducive to rapid propaga-tion, have already been established as test conditions. It was thus
natural that this te st apparatus should be considered as a means of investigating the possible hazard of using plastic light-diffusing panels.
For all the ceiling-mounted ASTM E84 tests 2-in. spacers were mounted along both shoulders of the tunnel to ensure that a cavity was
created between the test specimens and the roof of the tunneL All specimens were cut to a width of approximately 18 in. so that they rested on the shoulders of the tunnel. with an overlap of 3/8 in. The spacers supporting the roof were, in fact, 1 1/2 in. wide so that the remaining width of each shoulder was precisely this dimension. The ends of the cavity between the te st specimens and the roof of the tunnel were closed.
..
-4-It was appreciated that a speciInen should not be mounted directly over the burner because it might create problems on falling. The first speciInen was therefore mounted 5 in. in advance of the burner, preceded by non-combustible dummy specimens. A total of three 4-ft long speciInens was used of the type coded 2 in Table 1.
The test behaviour proved rather unsatisfactory because the end of the first section remote from the burner came down from its mounting (at 1 min). While subsequent sections were collapsing the first ignited and fire was propagated rapidly down the tunnel; the fuel was by then mostly on the floor.
A repeat test was arranged (designated No. 5 in Table II) with the leading edge of the first speciInen located 18 in. in advance of the centreline of the burners. The sequence of events was nluch more
satisfactory, the leading edge of each specimen falling first and no ignition occurl'ing prior to the end of the test, which was declared to be the tiIne after which all of the speciInens had fallen to the floor of the tunnel.
It is suggested that the result of this test (No.5, Table II)
indicates that the plastic diffuser involved would fail out without igniting under most exposure conditions conducive to a rapidly developing fire.
No satisfactory rationale was developed for the decision to close off the end of the cavity formed by the test specimens and the roof of the tunnel. Te sts Nos. 6 and 7 were therefore run with the cavity open at each end. The results (particularly No.6 as compared with No.5) suggested that there was little to choose between the two conditions and subsequent tests were run with the ends of the cavity closed.
Recapitulating the conditions established for test No.5, speciInen widths were cut so that they rested on the shoulders of the tunnel, with an overlap of 3/8 in. A total speciInen length of 12 ft was used, the leading edge of the first section being located 18 in. in front of the
centreline of the burner ports. Lightweight asbestos dummy speciInens preceded it. The cavity bounded by the light-diffusing panels was closed off.
Under the same conditions a number of other plastic lighting panels were subjected to the test (Table II). Materials 1 and 3 (Tests 7 and 20) were only 1 ft wid.e, and were mounted centrally on tees, the spaces on either side being masked with lightweight asbestos board.
Assuming the only satisfactory condition to be no ignition
before the end of the test (declared to be the tiIne at which all specimens had fallen out) the specimens not meeting this criterion were:
-5-(1) 1/2 -in. styrene egg crate (Test 13 and 19) (2) a 2- by 2-ft ribbed lens (Tests 17 and 18)
(3) the two thicker products from one particular manufacturer (Tests 25 and 26).
The rejection of the two thicker products from one manufacturer is worth discussing. It is possible that a corresponding test in a wider tunnel might give a satisfactory result; it would be desirable in view of the particular merits of (he lenses concerned. Such thick lenses are apparently called for where more uniform light distribution is needed.
The bending moment generated by a width of materials"1," suspended in the same way as for the test conditions varies as 1, 2; thus some repre sentation of a te st of the full width could be achieved by increasing the loading. A factor of 2 would probably be appropriate. A means of loading without substantially influencing thennal behaviour would need to be devised, but this work has so far not been undertaken. This discussion is predicated on the assumption that fall-out is associated with softening and bending. It is, in addition, dependent on shrinkage
of the specimen. This latter mechanism ｮＺｾｩｧｨｴ be represented on a
smaller scale by scaling the width of the supporting edge correspondingly. CSA-B54.9 FLAMMABILITY TESTS
When lighting panels fall from their mountings they may land on a floor or across desks or other furniture. Some account should be taken of their flammability in this context and the CSA B54. 9 test (for surface burning characteristics of flooring and floor covering materials) seems appropriate. The cut-off criterion that might be
chosen would depend on prevailing circumstances and would take into consideration the disposition of the lenses. The 1970 National
Building Code, in relation to high buildings, refers to a figure of 300 for floor coverings. This seems an appropriate figure to be
applied to lighting panels resting flat on a floor. Where panels may fall across desks or other furniture, however, a lower figure might be used, say 200.
Table III presents B54. 9 results on all but two of the lighting panels referred to in Tables I and II. It may be seen that only in one
case is the re suIt (200) within the range of value s that might be considered subject to limitation for general use.
CONCLUSIONS
A drop-out test using the CSA B54. 2 (ASTM E84) flame spread apparatus described appears to be practical as far as most commercial light ､ｾｦｦｵｳｩｮｧ panels are concerned. The fact that the majority would
-6-ne,ed to be cut down in size to fit the tunnel does not constitute any appreciable impediment.
In addition, a basic flammability test is required to assess the relative hazard of the materials after they have fallen from a ceiling and are located on a floor or on furniture. The B 54.9 te st appears to meet this requirement very satisfactorily.
ACKNOWLEDGMENT
Acknowledgment is due to A. Rose for the operation of the ASTM E84 tunnel and P. Huot and R. Lamirande for the remainder of the tests.
•
e
TABLE I
SPECIMEN MATERIAL CODE
e
NRC Nominal
Material Plastic Thickness Description Manufacturer
Code (in. )
1 Acrylic 3/32 Plane(1 ) 1- by 4-ft sheet A
2 Acrylic 3/16 Plane( l) 2 - by 4-ft sheet Po.
3 Acrylic 3/32 Hinged & ribbed edged
1- by 4-ft plan.e (1) sheet A
4 Acrylic 1/8 Plane( 1) 2- by 4-ft sheet B
5 Acrylic Plane (1) 2 - by 4 -ft she et B
6 Acrylic 1/8 Plane
(1)
2- by 4-ft sheet C7 Acrylic 5/32 Plane ( 1 ) 2- by 4-ft sheet C
8 Acrylic 0.2 Plane (1) 2 - by 4-ft sheet C
9
Acrylic-
Ribbed lens 2- by 2!"'ft A10 Acrylic
-
1/2-in.egg crate D11 Styrene
-
1/2-in.egg crate D•
e
•
TABLE II
TUNNEL DROP-OUT TEST RESULTS
Drop-out (sec) Ignited
Material First Section Ignition Before Before
Test Identifi- Near Far All Time In 1 st Section All Sections No
No. cation End End Sections ( sec) Place Fell Fell Ignition Remarks
7 1 45 54 185
-
J
Far end of false ceiling6 2 50 64 200
-
J}
not blocked off.5 2 58 NR(l) 175
-
J
20 3 20 30 147
-
J
15 4 5 52 155
-
J
16 5 5 45 160
-
J
24 6 5 50 100
-
J
25 7 8 60 145 10
J
Flame extinguished itself assheet completed fall to floor.
26 8 18 100 135 10
J
Sustained fire.17 9 45 70 220 50
J
Flame extinguished 'itself at70 sec as sheet completed fall to floor. Reignited on floor at 7 5 ｳ･｣ｾ Sustained fire.
18 9 45 67 22.8 50
J
Mounted upside down, i. e.ribs up. Sustained fire.
11 10 12 18 50
-
J
13 11 10 20 45 <25
J
19 11 8 16 45 8
J
TABLE III
B54.9 FLAME-SPREAD RESULTS
Material Flame -Spread
. Identification Rating (B 54. 9) 2 162 4 110 5 114 6 200 7 160 8 160 9 100 10 137 11 106
