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REFERENCEI NIST Technical Note 1465

A Study of Size Effects in the Fire

Performance of Beds

Thomas Ohlemiller

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• (a 1? I O^ National Institute of Standards and Technology • Technology Administration • U.S. Department of Commerce

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NIST Technical Note 1465

A Study of Size Effects in the Fire

Performance of Beds

Thomas Ohlemiller

Building Fire Research Laboratory

Gaithersburg, MD 20899

January 2005

ff ^v -^

U.S. Department of Commerce

Donald L. Evans, Secretary

Technology Administration

Phillip J. Bond. Under Secretary^for Technology

National Institute of Standards and Technology

Hratch G. Semerjian. Acting Director
Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such

identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the

entities, materials, or equipment are necessarily the best available for the purpose.

National Institute of Standards and Technology Special Publication 1465

Natl. Inst. Stand. Technol. Tech. Note 1465, 28 pages (January 2005)

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A Study of Size Effects in the Fire Performance of Beds

T. J. Ohiemiller

Abstract

Three mattress/foundation designs of varied fire resistance were tested witii the

California Technical Bulletin 603 protocol (TB 603, using a pair of gas burners

as the ignition source) and also with a set of heavy bedclothes ignited by a match-size flame. All designs were tested in both twin and king size; one

design was tested also in queen size. A major goal was to assess the possible

existence of a mattress size dependence in the response to the TB 603 protocol.

All testing was done inside a room (3.66 m wide by 4.27 m long by 2.44 m

high) with a single door opening half the width of a fully opened door. The

design yielding the lowest peak heat release rate (HRR) showed no mattress size

dependence. The two other designs were more ambiguous but showed no size

dependence in their response judged against the TB 603 pass/fail criteria. The

bedclothes fires atop the lowest HRR mattress showed a large size dependence

in their HRR peak. The queen and especially the king size bedclothes peaks were large enough to pose serious secondary ignition threats in a realistic

bedroom context. When tested atop the other two, less resistant, mattress

designs, the bedclothes fires yielded controlled fires for the twin size but

runaway fires for the king size.

Introduction.

The Consumer Product Safety Commission is considering a regulation of the

flammability behavior of mattresses and their associated foundations. The probable test method at the heart of this regulation is expected to be closely analogous to that described

in California Technical Bulletin 603. In that protocol, a twin size sample of the mattress

and foundation is subjected to a pair of gas burners designed to mimic the local heat flux

conditions imposed by burning bedclothes. The heat release rate (HRR) that ensues from

this exposure is measured over a 30 min period. In TB 603, the peak HRR must not

exceed 200 kW in this period for a mattress/foundation design to be acceptable.

The TB 603 protocol accepts testing in either an open hood environment or in a burn room. A substantial fraction of the available fire testing facilities in this country can use only a burn room environment. A room can impact the intensity of burning of an object

in ways described below. Previous data [1] indicated that TB 603 results would not be

expected to depend on the ambient surroundings (room vs. open hood) as along as the

pass/fail limit was as low as 200 kW. The same study showed that some effect of the

room environment on the fire could be seen for higher peak HRRs [11.
Roughly two-thirds of the beds now being sold in this country are larger than twin size.

On the other hand, the fire test facilities that use burn rooms cannot accommodate any

size larger than twin. When burned under an open hood, unimproved beds (i.e., those

having no fire protection) larger than twin size give higher peak HRR values than those seen with twin beds. This raises the issue as to whether tests of twin beds of less

flammable design might underestimate the heat release rate behavior to be seen in larger

beds. Since real world bed fires occur in rooms, this issue must be considered in light of

the possibility that room effects may influence the magnitude of any bed size effect that

is seen. Bed size effect on peak HRR, in the context of a room, is, therefore, the subject

of the present study.

A room environment can impact a burning process within it by at least two mechanisms.

The first mechanism (and the principal concern here) involves thermal feedback to the

burning surfaces on the bed. When any object is burning in a room, the buoyant, hot

smoke rising from the fire is captured beneath the ceiling, forming a layer at least as deep

as the distance between the ceiling and the top of any opening (a door or window)\

Because of its soot content, such a layer is typically a good radiator of heat, especially as

its temperature rises due to continuing heat input from the fire. Downward radiation

from the smoke layer can impact the rate of spread and HRR of the fire feeding this

smoke layer, especially for exposed burning surfaces that face upward. (In contrast, a

fire with little unobstructed view of the hot upper layer, such as an internal foundation

fire, would show little or no response.) Surfaces that are affected then contribute more

heat to the upper layer, further enhancing the feedback to themselves. The potential thus

exists for a strong enhancement of overall HRR from upward facing surfaces. Exposed

vertical surfaces may show a weaker response due to their lesser view of the radiation

from the smoke layer.

The other mechanism by which a room environment affects a fire is oxygen limitation.

With an open window or door, this only comes into effect as the room approaches

flashover and so much material is burning that the opening cannot supply the needed air

(while still allowing hot smoke to escape). Since this limitation comes into play at a HRR of about 1 MW for existing test rooms, it is not a concern here.

The susceptibility of a mattress to room effects in a TB 603 test is design dependent. In

particular, the amount and location of continued flaming after the gas burner exposure

varies with design. As noted above, burning zones on top of the mattress are most hkely

to experience direct feedback from the smoke layer. For this reason, three different

designs (all having greatly reduced flammability relative to current commercial practice) were used in this test, though there was no way to select a priori designs prone to top

surface burning. An attempt was made to find designs likely to give differing HRR

levels.

' A closed room will behave in a more extreme manner since smoke cannot escape. The smoke layer will

fill the room, encompassing the fire, and when the available oxygen drops (to the neighborhood of 10 % to 15 %), the fire will go out. It may take little burning to reach this condition (ca. 1 kg for a small bedroom)

and room conditions will be hazardous before this point is reached [2]. This situation is not addressed here.
The TB 603 protocol mimics (by means of the pair of gas burners) the local heat flux that

burning bedclothes bring to bear on a mattress or foundation. It does not mimic the

complete fire behavior of burning bedclothes. Local ignition of a full set of bedclothes

by a match size flame leads to a spreading fire on the bedclothes assembly that typically

grows (in an open hood environment) to a maximum burning area in the region of 1 m'

to 1.5 m". The burning area does not grow larger than this because the spreading flame

front is followed by a burn-out front which represents the point at which all of the layers

have been consumed. The burning zone (between the ignition front and the burn-out

front) spreads over a bed in a time of the order of 10 min. Twin size bedclothes

themselves may give a HRR peak of 200 kW or more. They too are thus potentially

subject to room heat feedback effects. In examining bed size effects in this study, some

tests of each design were therefore carried out with burning bedclothes rather than the TB

603 gas burners. ts*-

Experimental Details.

All of the mattress designs were based on box springs in their interiors. Other available

details were as follows:

• Design AA was a two-sided tight top mattress that utilized flame-retarded cotton

as both a barrier and as part of its cushioning. The material in the mattress side

panels was not identified. The foundation was based on conventional linear wire

springs attached to a wood base; it had a continental edge.

• Design BB was a high-end mattress with a velour ticking and extra thick

top/bottom padding. It also was a tight top design. It utilized a high loft barrier

under the ticking. Its foundation contained coil springs attached to a wood base;

it had a continental edge.

• Design CC was a two-sided pillow top mattress that used an unidentified barrier

layer under the ticking. Its foundation was unusual in having a full threedimensional wood frame; it also had a continental edge.

Two of the mattress designs, AA and CC, were tested in twin and king size; design BB

was tested in queen size as well. Twin and queen size mattresses both have one piece

foundations. King size mattresses are supported by a pair of foundations, each

approximately the size of a twin foundation.

The test room layout is shown in Figure 1. The interior was 3.66 m wide by 4.27 m long

by 2.44 m high (12 ft by 14 ft by 8 ft). This room size represents a compromise between

two opposing factors: (1) a desire to maximize room effects by keeping the room small

and (2) a need to have a room sufficiently large for a king size bed plus the gas burner

assembly. The wood frame construction was lined with 1.3 cm thick calcium silicate

board above the mid-height; this lining was full-height over the 2.3 m wide wall section

where the head of a bed was nearby. The remainder of the room was lined with 1.3 cm

thick gypsum board. However, the area under the bed was covered with 1.3 cm fibercement board. These lining materials precluded any significant heat release

contributions from the paper lining of the gypsum board; the other lining materials are

inert. The thermal properties of the calcium silicate board lining the walls and ceiling are
comparable to gypsum board except in the temperature range from about 120 °C to 210

°C where gypsum dehydrates and effectively behaves as if it has a much larger heat

capacity. In the present tests this means that the walls and ceiling will tend to heat more

rapidly than gypsum board in this temperature interval. Since wall heat-up is a relatively

slow process" compared to other critical processes in these tests, this difference in

thermal properties is not believed to have any significant effect here.

The fiber-cement board under the bed is likely also to be different in its properties from

materials such as wood flooring that might be found in real bedrooms. This could mean

that the development of a melt-drip fire on the floor differs here from such an event in the

real world. None of the mattress designs examined exhibited any marked tendency to yield a melt/drip fire on the floor. In the absence of bedclothes, the only flaming melt

material that reached the floor was from the dust cover on the bottom of the foundation;

this created minimal fires of no real concern. Flaming bedclothes frequently drop

burning material to the floor; the resulting layers are typically thick enough for their

burning to be uninfluenced by the floor material. Carpeting under a bed may make some

of these floor fire issues more serious but that issue was not examined here.

The bed foundations were placed atop steel bed frames 10 cm to 1 1 cm high (essentially

the same as those specified in TB 603). Precautions were taken to preclude an issue

noted previously with the 2.5 cm wide steel angle used in the twin frame specified in TB

603. It had previously been found that when a foundation, with its typically rounded

corners, was placed atop the square-cornered bed frame, a small gap (up to several mm)

appeared between the frame and the foundation corner (at all four comers). This gap

appears to offer a potential path for small flames on the ticking of the foundation to reach

the underside of the foundation. Such behavior was never actually witnessed in several

closely-watched tests but the potential for it was deemed an unrealistic artifact of the narrow support frame (real bed frames tend to be wider than 1 inch). Here each comer of

the bed frame was covered diagonally with a double-layer swath of heavy duty aluminum

foil to close off this gap.

The room had two openings. That shown at the top in Fig. 1 was an access door which

was open during the burner exposure. It was closed immediately after the bumer was

removed through it. Its periphery was sealed with ceramic wool. The other opening, that

in the left wall in Fig. 1, represented a partially open bedroom door and it remained fixed

except when the test sample was being moved in or out of the room. By not being fully

open, this doorway yielded a somewhat restricted air flow to the fire. The intent was to force the smoke layer temperature upward somewhat to enhance the room feed back

effect in the same manner it would be if a bedroom door were partially closed. This also

forces the smoke layer to be thicker (lower). For these tests it was not considered

desirable to have the smoke layer so low that it obscured the fire on the top of the bed.

CFAST" predictions were used to select the half-normal doorway width used throughout

' The time for a temperature wave to penetrate a 1.3 cm calcium silicate board is of the order of 20 min.

The wall or ceiling will thus require a time of this order to lially respond to the hot smoke layer with which

It IS m contact

3 CFAST is the NIST Consolidated Fire and Smoke Transport model.

4
these tests. Those predictions indicated that the smoke layer temperature would be

increased by roughly 60 °C (relative to the fully open door case) if the fire peaked at around 400 kW. The corresponding change in maximum radiative feedback from the

smoke layer (taken as a black body with a view factor of unity for the top of the bed) was

from 4.6 kW/m" to 7.0 kW/m'. These calculations treat the fire as having a single,

concentrated plume. In reality the fires tended to be strung out linearly and spatially

patchy. This could be expected to enhance room air entrainment, lower the smoke layer

temperature and thus decrease the actual radiative feedback below these estimates.

For differing bed sizes, the burner-exposed side was always in the position shown in

Fig. 1 . (The position of the opposite side of the bed relative to the wall at the bottom in

Fig. 1 thus varied with bed size.) Thus any effect of the airflow into the room on the

early part of the bed fire should have been independent of bed width. In practice, the air

flow did not appear to have any noticeable effect on the bed fire. The head of the bed

was always placed approximately 13 cm from the wall. This allowed burning to progress

along this side of the mattress and foundation.

As Fig. I indicates, the half open door was located beneath the hood of the NIST 3 MW

calorimeter to permit HRR measurement. The details of this device are discussed fully in

Ref. 3. The expanded relative uncertainty for the larger fires recorded here (several

hundred kW) is ± 1 1 %; for the smallest fires (below 50 kW) the expanded uncertainty

rises to ± 27 %.

Two of the windows were used for video cameras, that in the upper wall and that in the

lower wall, as seen in Fig. 1. The fields of view of both cameras were less than the

length of the bed so the cameras had to be panned to follow fire spread. An observer

could also use the half open door. In general, viewing of the fire behavior was much less

satisfactory than that which is possible in an open hood.

The tests were conducted in a randomized order but all tests of a given size bed were

grouped together. This was a concession to the awkwardness of moving the heavy king

size bed frame in and out of the room.

High ambient humidity during much of this test series led to a potential source of

baseline drift in the calorimeter readings. It was noted that by about 30 min into a test, there were signs that water vapor was just beginning to penetrate the water trap system

and reach the oxygen meter where it caused some signal drift. Since the TB 603 cut-off

time is 30 min, the data were logged up to that time. Immediately, after this, while the

test continued, the calorimeter system was switched off line for 5 min while the water

traps were replaced. Each test then continued for a full test period of 60 min (unless the

fire was extinguished, as discussed below). In only one test did this gap in the data lead

to a significant loss of pertinent results. That case was for an AA design with bedclothes.

The second peak was missed; its size was estimated visually from the flame volume and

previous experience.
To preclude fire damage to the room lining, some of the tests were stopped before they

reached their full intensity. In the early tests the stopping point was as low as 400 kW.

As experience with the behavior of these systems was gained, the stopping point was

raised to 800 kW. This left some ambiguities in the interpretation of certain results,

discussed below, that had to be resolved through other sources of information. When a

fire is referred to below as a "runaway fire", it was, in the author's judgment, on its way

to flashover at the time it was extinguished. 'c

Results and Discussion

Table 1 summarizes the data obtained in this study on peak HRR and time to that peak.

Tests in which the fire was extinguished before it reached its full intensity are denoted by

a bold E. Gas burner tests with twin size samples of design BB all gave very low heat

release rates. The timing of the very weak, post-burner peaks was difficult to quantify;

this is indicated in the Table.

Gas Burner Tests. Figure 2a summarizes the peak HRR for the gas burner tests as seen over the full 60 min test period. The time to the peak or the time of extinguishment is also shown on each bar (which represents one test). The results nearly all fall at the

extremes of HRR behavior, giving either very small or very large fires. Thus all tests of

design BB gave essentially only ticking fires . These fires were most persistent in the

peripheral crevice between the mattress and foundation (a behavior seen often in other

studies [4, 5] ) and these crevice flames became most intense in the corner areas. A break

in the barrier (on the mattress side, near a comer, in the last 15 min of the test) was seen only once in these BB tests and it appeared to have no adverse consequences by the end

of the test.

Clearly, there was no significant size effect with the TB 603 burners when they were

applied to design BB. Here the fire had no scale dependence. It amounted to a rather

patchy and variable burn zone(s) propagating in the mattress/foundation crevice. (The

fire on the mattress top went out soon after the burners were turned off.) The burning zones were variable in length and time reaching 1 m or more in width in some cases. The

HRR from such a fire has no dependence on the total length of the crevice that it is in

since it never occupies that full length at any one time. In fact the crevice fires never even made it all the way around the full periphery of the twin size beds in the 60 min

tests. At the same time, the small HRR of the crevice fires means that they have no

chance of building up a smoke layer in the room hot enough to yield any noticeable

feedback to the burning process. Thus there is no mechanism for a mattress size effect in a case like this.

The king size BB, as well as the other mattress designs, had, as noted above, a two part

foundation. The crevice between the two foundations, which lay under the longitudinal

centerline of the mattress, appeared to form an area of potential vulnerability. The

^ Such a fire appears to involve only the ticking itself. In actuality, especially when it persists in the crevice

area, it is likely that it is also consuming pyrolysis vapors from the barrier (a charring organic material)

below the ticking and possibly even from material layers below the barrier.
horizontal mattress/foundation crevice fire, when it reached this vertical crevice between

foundation sections, would intensify and "bore in". That is, the fire moved inward into

the vertical crevice over the full foundation height, seeming to form a chimney as the

foundation side materials charred and shrank, leaving space for an improved air supply.

Any flames in this chimney impinged on the bottom of the mattress. As threatening as

this appeared in the tests performed here, it did not noticeably change the results with any

of them. The BB design could withstand this; the other designs were in trouble for other reasons by the time this effect came in to play. However, since this is a feature unique to king size beds and is thus not tested in TB 603, it is worth bearing in mind when barrier

materials are chosen.

When tested with the gas burners, the king size versions of designs AA and CC all gave

runaway fires that were extinguished as they passed 800 kW. Note that this occurred sooner with design AA than with design CC; design CC easily passed the TB 603 criteria

whereas design AA did not. Aside from this, the HRR results in Fig 2a do not allow a

distinction between the two designs since all of the tests were halted. Visually it was

apparent early-on that the flames on the sides of the AA design were substantially more

intense; the laterally spreading fires (moving in opposite directions from the ignited

region) covered the entire height of the mattress and foundation side rather than being

essentially confined to the mattress/foundation crevice as with design BB and CC.

Similarly, design AA showed a continuing, radially spreading flame zone on top of the

mattress whereas designs BB and CC did not.

Figure 2a seems to show a much lesser fire intensity from both AA and CC twin size

beds, as compared to the king size versions of the same designs. In fact, any size effect

was not nearly so pronounced, as will be seen.

Consider the AA case first. All of these fires, for both bed sizes, looked essentially alike

in terms of fire growth patterns and HRR for roughly the first 20 min. They looked like

the king size design AA fire described above. The mechanisms behind their increased

HRR after about 20 min were the same - foundation fire growth coupled with some

evidence of interaction with the wall on the head end of the bed. The HRR up to this

time (less than 80 kW) and the location of a significant fraction of it within the

foundation precludes a sufficiently hot upper smoke layer and a sufficient fire area in its radiative field to initiate room feedback effects. Even the one design AA test which did

not run away, the first twin test, started to run away due to a foundation fire; for reasons which were not apparent, in this one case, the foundation fire did not yield an increased

mattress fire before everything died back. In any event, prior to runaway, the fires were

all too small to interact with the room and the runaway was by a mechanism which did

not depend on mattress size. Thus the second and third design AA twin tests were very

likely on their way to fire sizes as large as were seen in the king size tests (before the

king beds were extinguished) but these twin bed fires were stopped earlier in this fire growth process. This is not to say that the king size mattress would not ultimately give a larger fire than the twin size mattress but both would likely have pushed a room toward

flashover on essentially the same time line. Thus, from the viewpoint of ilashover

prevention or from the viewpoint of TB 603 pass/fail, the two mattress sizes were equal.
The increased threat represented by the king size AA mattress design is probably to spaces beyond the room of fire origin.

The CC mattress designs are somewhat more ambiguous as to mattress size effect on

overall fire behavior. The first twin bed test involved a defective sample - the barrier

was missing from one quarter of the mattress periphery - and so that result must be

discarded. The fires in the other samples of both sizes started and grew in very much the

same manner, primarily along the mattress/foundation crevice initially. Eventually this

fire would reach the vertical mattress seam at the foot end. This seam appeared to lack

combustion resistance and would open rather readily, allowing flames into the mattress

interior. The fires would thus grow from the foot end on and into the mattress. Sometimes this was abetted by growth from the head end, on the mattress top, as well.

Partial foundation involvement, generally late, was seen only with the twin mattresses,

for no evident reason. Late in the tests, the larger top area of the king mattresses began to make a difference in that it yielded a sufficient HRR to generate room feedback. This

caused the king size mattress fires to run away, with minimal evident contribution from

the foundations. The twin mattresses developed the same mattress top/interior fires on

approximately the same time scales but did not run away before 60 min had elapsed.

Both of the twin size fires appeared capable of running away, given a little more time,

and one was in fact rapidly increasing in HRR at 60 min when it was suppressed. The net

result is that the king size mattresses did run away late in all three of their tests while the

twin size mattresses appeared to be approaching this point when the tests ended. Here, at the very least, the effect of bed size was to shorten the time to a runaway condition by

several minutes. Since the tests were ended at 60 min, we cannot be certain that the CC

twin bed fires would have run away or merely become larger and more threatening as

their foundations began to burn more extensively along with the mattresses. Again there

was no size effect on TB 603 pass/fail (both sizes passed).

Figure 2b shows the peak HRR results that were seen within the first 30 min of the test. These thus indicate directly which specimens passed the 200 kW limit (anytime in the

first 30 min) set in TB 603. As noted above, design AA had only one pass, a twin

mattress. Design CC had only one fail, a twin mattress but, as noted above, this specimen

was defective, lacking a portion of its mattress side barrier. All of the design BB

specimens passed the TB 603 HRR criterion. The general lack of a mattress size effect on TB 603 passage or failure can be seen in Fig. 2b.

Overall the effect of bed size was minimal, having a definite effect only in the case of the

CC mattress design. It was this design which showed the greatest vulnerability to room

feedback by virtue of burning extensively on the mattress top surface. Even here the

effect was exhibited only late in the tests and may have amounted only to a shortening of

the time to a fire size which threatened flashover. A definite contributor to the CC

mattress burning behavior was the poor heat resistance of the thread in the vertical side

seam placed here on the end away from the wall. This allowed a relatively early passage

of flames into the mattress interior. Had a more resistant thread been used, it is possible

that the runaway behavior seen here would have been pushed beyond the 60 min point.
On the other hand, burning bedclothes would find any such vulnerability much sooner, so

lateness in a test does not necessarily mean an event is non-threatening in the real world.

Appendix A discusses barrier materials in general terms and some issues related to how

and when they might show vulnerabilities in a TB 603 test and also in a real world fire involving burning bedclothes.

Bedclothes Tests. As noted in the Introduction, real world bed fires usually involve

burning bedclothes initiated locally by some small flame source. Current commercial

bedclothes, when ignited locally, will allow progressive flame spread over their entire

outward facing surface in a time of the order of 10 min. Since this fire is on surfaces

facing upward and sideways in a room environment, it is again in the right position to be

influenced by radiation from hot gases accumulating in the upper part of the room.

It was noted earlier that the burning area on bedclothes (under an open hood) reaches a roughly steady value that is much less than the total outer area of the bedclothes. Thus, if the HRR per unit area of bedclothes is small enough, there will not be enough total HRR

from the bedclothes to push the upper smoke layer into a domain where radiant feedback

is significant. In other words, despite the fact that the situation is, in one sense, primed

for significant feedback and therefore a strong size effect, it does not necessarily occur.

There are two other parameters of this problem, as well. First is the sensitivity of the

burning rate of the bedclothes assembly to added external radiation. This type of

sensitivity is readily measured in a device such as the Cone Calorimeter where the

behavior of a sample subjected to various fixed levels of radiant heat flux is measured.

The other parameter is the ignitability of the topmost layer of the bedclothes; here this is the cover fabric on the comforter. If this layer readily ignites" in the combined heat from

flames spreading on top of the bedclothes plus radiation from the hot smoke layer, the

spreading flame front it represents will run further and further ahead of the burn-out front on the bedclothes. The net result is that the area of burning bedclothes increases beyond

that steady-state value seen in an open hood and the net total HRR goes up, increasing the

smoke layer temperature, which, in turn, increases the smoke layer radiation back to the

bedclothes, etc. The stage is set for the HRR to run upward. Since the total bedclothes

area is bigger for a larger bed, the HRR from the larger bed can run further upward.

Putting together all of the above parameters to determine their net effect and thereby

predict the overall behavior of burning bedclothes in a room enclosure requires a

sophisticated model such as the NIST Fire Dynamics Simulator (FDS, Ref. 6). That

remains for a future study. Here we confine our observations to the experimental results

obtained for one set of bedclothes.

Figure 3 shows the results of this type of scenario on top of design BB beds of three

sizes. As noted in the Introduction, the fires were started by applying a match-size flame

to the bottom forward (head end) edge of the folded back region of the hanging

^ Ease of ignition for a fabric like this depends both on its chemical stability and also on its weight per unit area. Thinner (lighter weight) fabrics will be more rapidly ignited.
bedclothes. The early HRR peaks, in the first 1000 s, are dominated by the bedclothes^.

There is quite clearly a major bed size effect on the burning of the bedclothes in this

room context; the peak HRR goes from about 260 kW for the twin size bed to about 800

kW for the king size bed. Note that the HRR curves begin to depart from one another in

the neighborhood of 200 kW, roughly 4 min to 4.5 min after ignition. The differences in

burning area that prompt this early divergence are too subtle to be seen in the restricted- access videos taken of these tests. Later one can clearly see the effect of radiative preheating well ahead of the spreading flame front on the comforter in the king size case; the

heat causes the cover fabric on the comforter to wrinkle, possibly because the polyester

fibers in it are melting. Note that the king size bedclothes, with their roughly doubled

area and mass relative to the twin size bedclothes, burned up in a time that was

essentially the same as that for the twin size bedclothes.

The size of the bedclothes HRR peak in the king size bed case is truly remarkable and it poses a substantial flashover threat by itself (i.e., via ignition of secondary objects placed

nearly anywhere within the same room) using the criteria developed in Ref. 1. Even the

queen size peak is threatening in the presence of other significant flammable objects in

the bedroom.

Figure 4 shows how the bedclothes HRR peak size on design BB beds relates to the top

area of the bed. Note that the least squares fit line is second order in bed area. This

greater than linear dependence follows from the increasing heat feedback which a larger

bed receives from the hot smoke layer in the room environment.

The impact of this intense bedclothes fire on the bed beneath it is clear in

Fig. 3, in the HRR behavior after the bedclothes peak. Recall that, after the gas burner

exposure for design BB, there was persisting flaming but minimal HRR peaks, regardless

of mattress size. Here, after the bedclothes fire died back, there was an extended lull and one saw again the types of localized flaming that the gas burners exposure induced -

mainly persisting crevice flames. For the twin bed, while the gas burners produced longlived crevice flames (ca. 20 min to 25 min), especially at the corners, for this design, the

bedclothes produced corner flames that lasted even longer''. This appeared to be the source of the second, later flare-up for the twin size bed in Fig. 3. Persisting comer

flames eventually got a fire going in the mattress interior; there was no evident

foundation involvement.

^ The HRR here is predominantly but not exclusively due to the bedclothes. The top and sides of the mattress are contributing some heat but there is no way to distinguish that portion. Design BB was chosen

for this because, on the basis of the gas burner tests, it was believed that it would contribute the least to the bedclothes HRR peaks.

A substantial difference between the gas burner exposure and the burning bedclothes exposure is the total amount of heat deposited in the mattress/foundation. The greater heat content in the case of the bedclothes

fire apparently favored a continued fuel supply to the crevice flames, sustaining them long enough to burn

through the mattress barrier.

10
The king size bedclothes fire, on the other hand, constituted an exposure to the mattress

that was far more intense than those^ measured in Ref. 7 and which were the basis for the

design of the gas burners. Indications of this increased intensity were evident on the

video tapes. A horizontal flame front was driven down the sides of the foundation by the

hot smoke layer radiation. Two strong puffs occurred in the mattress as the bedclothes

peak was receding. Two and possibly more holes appeared in the mattress side barrier;

these were conceivably caused by the over-pressurization during the puffs but they were

not visible until several minutes afterward. It was these holes which allowed flames into

the mattress interior and eventually yielded the second, large HRR peak (which was

extinguished).

The overall behavior of the queen size BB mattress with bedclothes was comparable.

There was a weaker puff in the mattress followed later by multiple holes in the mattress

side barrier which led to an interior mattress fire that provided the second HRR peak.

The gas burner exposure cannot be expected to be a good predictor of response to the

queen and king size bedclothes fires in a room context since these fires are more intense

than that which the burners mimic. On the other hand, these bedclothes fires constitute a

substantial threat in themselves and, furthermore, they are not delayed like the

mattress/foundation fires.

The preceding results do indicate that if the queen and king bedclothes fire size was

limited to the 200 kW size specified in TB 603 for mattresses, it is likely that the later

mattress fires seen in Fig. 3 would also be brought under control.

Bedclothes tests were also conducted with designs AA and CC in twin and king size (one

test each); the results are summarized in Fig. 5. Mattress design clearly has a major

effect on the peak HRR during the bedclothes fire; see Fig. 6 for the twin size beds. The

AA design more than doubled the peak HRR seen with the BB design. For design AA

even the twin size bedclothes fire peak is a substantial secondary ignition threat by the

criteria given in Ref. 1 . Designs BB and CC are much less threatening in this regard.

Figure 6 is a clear illustration of the extent to which the mattress and foundation can, in

some cases, contribute heat to the bedclothes peak. In the case of the AA design this

appeared to take the form of prolonged burning of the upper layers of the mattress during

and after the bedclothes fire passage. Eventually this led to multiple holes in the mattress

and finally a combined mattress/foundation fire to yield the second, later HRR peak. The

behavior of the CC twin design was similar, though less intense and slower to yield a mattress/foundation HRR peak. Again there were indications that the bedclothes fire was

partially compromising the protective barrier on the mattress and thereby extracting more

heat from the system.

When the same type of bedclothes were burned atop king size versions of designs AA

and CC, the room-enhanced bedclothes fire proved to be too much for the mattress

barriers and the bedclothes fires had to be extinguished as they passed 800 kW; see Fig.

Various sets of twin-size bedclothes were burned in an open hood atop a special inert mattress. The

bedclothes set most comparable to that used here gave less than 200 kW as its peak HRR.

11
5. In the case of design AA, all outer surfaces (mattress top and sides plus foundation

sides) were caught up in the strong room feedback and forced to burn with enhanced

intensity. There did not appear to be time for the interior of the mattress or foundation to make much contribution by the time the fire was suppressed.

12
Conclusions.

The significant conclusions from this study are as follows:

• When tested with the TB 603 gas burners and in a room context, a mattress/foundation design yielding only a very low HRR (design BB) exhibited no signs of a size dependence in its burning response.

• The results for designs yielding greater HRR were somewhat obscured by

differing test termination conditions. However, close inspection of the available

evidence indicates that design AA would yield runaway fires at essentially the

same time regardless of mattress size. Both fires would thus have failed the TB

603 HRR criteria in the same time frame though the fire from the larger bed

would probably ultimately be larger. Design CC, with HRR results falling

between those of BB and AA, appeared prone to yield somewhat more rapid fire development with the larger mattress and the fire size was possibly prone to be

larger as well. Both sizes of Design CC would easily pass TB 603 criteria since

all fire growth was in the last 15 or less minutes of the 60 min test period.

Bedclothes fires were found to be strongly dependent on bed size when burned in a room context. This appeared to be the result of a combination of physical

parameters which favored maximal response to the heat feedback from the hot

smoke layer to the burning bedclothes.

The peak HRR from queen size and, especially, king size bedclothes was found to constitute a strong secondary ignition threat and thus would be likely to produce

flashover in many real world fires. The threat is enhanced by the fact that this

peak occurs within 5 min to 6 min of ignition by a match-size flame.

The room-enhanced bedclothes fires for king size beds overwhelmed the

protective barrier of two of the designs (AA and CC) leading to runaway fires

during the bedclothes peak. Even the most resistant design (BB) was

compromised by these enhanced bedclothes fires (queen and king size) and

eventually yielded runaway fires.

•

13
Acknowledgments

The work was sponsored by the Consumer Product Safety Commission. The CFAST

calculations were performed by Richard Peacock. Jack Lee, Bob Anleitner, Laurean

Delauter, Ed Hnetkovsky and Alex Maranghides were instrumental in setting up and

carrying out the fire tests.

References

1) Ohlemiller, T. and Gann. R., "Estimating Reduced Fire Risk Resulting from an Improved Mattress Flammability Standard," National Institute of Standards and

Technology Technical Note 1446, August, 2002

2) Jones, W., Forney, G., Peacock, R., and Reneke, P., "Technical Reference for

CFAST: An Engineering Tool for Estimating Fire and Smoke Transport,"

National Institute of Standards and Technology Technical Note 1431, March,

2000

3) Bryant, R., Ohlemiller, T., Johnsson, E., Hamins, A., Grove, B., Guthrie, W.,

Maranghides, A. and Mullholland, G., "The NIST 3 MW Quantitative Heat

Release Rate Facility," National Institute of Standards and Technology Special

Publication 1007, December, 2003

4) Ohlemiller, T. and Gann, R., "Effect of Bedclothes Modifications on Fire

Performance of Bed Assemblies," National Institute of Standards and Technology

Technical Note 1449, February, 2003

5) Ohlemiller, T., "Flammability Tests of Full Scale Mattresses: Gas Burners versus Burning Bedclothes," National Institute of Standards and Technology NISTIR

7006, July, 2003

6) McGrattan, K., Forney, G., Floyd, J., Hostikka, S. and Prasad, K., "Fire Dynamics

Simulator (Version 3): User's Guide, National Institute of Standards and

Technology NISTIR 6748, November, 2002

7) Ohlemiller, T., Shields, J., McLane, R. and Gann, R., "Flammability Assessment

Methodology for Mattresses," National Institute of Standards and Technology

NISTIR 6497, June, 2000

14
Table 1. Summary of Peak HRR Data from CPSC Bed Size Study

Design / Size / Ign. Condition Replicate Values of Peak HRR (kW) @ Time (s)"

AA / Twin / Gas Burners 140 @ 1648 408 @ 1460 /E 550 @ 1249/E

AA / King / Gas Burners >800@ 1574/E >800@ 1625/E >800@ 1534/E

AA / Twin / Bedclothes/ Pk l'" 552 @ 603

AA / Twin / Bedclothes/ Pk 2 ca. 500 @ ca. 2000

AA / King / Bedclothes/ Pk 1 >800 @ 488 / E

AA / King / Bedclothes/ Pk 2

-

BB / Twin / Gas Burners ca. 25 @ ca. 2000 ca. 15 @ ca. 3600 ca. 15 @ca. 3600

BB / Queen / Gas Burners ca. 25 @ca. 1800 ca. 20@ca. 1800

BB / King / Gas Burners ca. 25 @ ca. 3200 ca. 25 @ ca. 3400 ca. 25 @ ca. 3600

BB / Twin / Bedclothes/ Pk 1 265 @ 470

BB / Twin / Bedclothes/ Pk 2 175 @ 3358

BB / Queen / Bedclothes/ Pk 1 508 @ 524 525 @421

BB / Queen / Bedclothes/ Pk 2 >800 @ 2558 / E >800@3197/E

BB / King / Bedclothes/ Pk 1 794 @ 404 / E 800 @ 409

BB / King / Bedclothes/ Pk 2 - >800 @ 2402 / E

CC / Twin / Gas Burners >378 @ 1693/

E"

140t @ 3600 50 @ 3243

CC / King / Gas Burners >800 @ 3492 / E >800 @ 2734 / E >800 @ 3235 / E

CC / Twin / Bedclothes/Pk 1 338 @ 508

CC / Twin / Bedclothes/Pk 2 314 @ 2444

CC / King / Bedclothes/ Pk 1 >800 @ 456 / E

CC / King / Bedclothes/ Pk 2 -

HRR peak corrected for baseline drift and calorimeter calibration; averaged over 10 seconds around

absolute peak; /E means tire was extinguished starting at time shown

Pk 1 is first peak and is dominated by bedclothes burning; Pk 2 is second peak and is dominated by

mattress and foundation burning

High HRR due to missing section of barrier material. | for second test result indicates climbing HRR.

15
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18
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21
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Figure 6. Effect of Mattress Design on Peak HRR During Bed Clothes Burning.

Results are for Twin Beds.
Appendix A

Expected Effects of Various Barrier Imperfections on

Heat Release Rate Performance in TB 603

Introduction. It is of interest to explore how various barrier imperfections could be

expected to be reflected in the HRR curves obtained from a localized gas burner test such

as TB 603 and from an actual bedroom fire. Ultimately, it is essential that inferences

made from TB 603 behavior carry over (though not necessarily in a one-to-one manner)

to real bed assemblies in which the bedclothes are the first items ignited. All results to date indicate that this will be so for twin mattresses. However, the results in the main

body of this report indicate that the bedclothes fire can be magnified to the point of

dominance on larger beds (queen, king) in a room context. In such cases, mattress/foundation barrier performance (as measured in TB 603) is still relevant to the

size of the total fire but it does not control the timing of that fire nor fully dictate its peak

intensity.

This discussion is predicated on the assumption that the burning bedclothes fire is itself

reasonably controlled so that the dominant fire load in the bed assembly is the

mattress/foundation. This dominant fire load controls the magnitude and timing of the

highest HRR peak though both elements may make significant HRR contributions.

Background Discussion of Fire Barriers. The barrier on a mattress and foundation

design covers a large fuel load within its boundaries. Given sufficient air and flame

access to some part of that fuel load, a growing fire will occur, though there will almost

always be some limitation on the speed of growth and peak HRR of that fire as a result of

the presence of even an imperfect barrier.

The use of barriers in this way tends to raise the possibility of "binary" behavior, i.e., the

outcome of an ignition exposure can either be a minimal fire if the barrier on the

particular sample exposed is fully effective or a substantial fire if the barrier at some

point allows flame penetration to the large fuel load within its bounds. This type of

behavior poses difficult statistical issues in its assessment. Achieving a high confidence

level that a barrier design is effective can require a large number of test replicates. On

the other hand, attention to detail in designs that use barriers coupled with attention to uniformity of fire resistance in barrier materials can go a long way toward preventing the occurrence of localized weak spots that might allow a significant fire. A barrier works by limiting heat and air access to the flammable material within it. The

ideal barrier would, at any point on its surface, never let enough heat through to the

material inside to cause that material to gasify at all, despite an intense fire on the barrier

exterior. If that was the case, the only heat that would be released would be from

material exterior to the barrier (and possibly from the barrier material itself). Cost will

generally preclude such a heat impermeable barrier. Real barriers do permit degradation

and partial gasification of polyurethane foam within them (in particular, the foam

immediately adjacent to a barrier surface that is exposed to flames). This is a transient

23
effect with more heat penetration and attendant foam degradation occurring as the

duration of flaming exposure is extended.

Because the barrier must allow normal functioning of the structure it covers, it must be

somewhat permeable to air (to avoid a "balloon" effect). That permeability should be

kept low enough so as to preclude flaming combustion inside the barrier even when

pyrolysis gases accumulate there. However, the requisite air supply rate to sustain

flaming may be a complex inverse function of the size of the heated area and the heating

duration so this condition may not be met indefinitely in a real fire. That is, at some point

in the growth of a bed fire, it may be possible to sustain a weak fire in the interior of a mattress even though the barrier is essentially intact.

A barrier material is porous but its pores must be small enough to preclude direct flame

propagation through them. Generally this means pores smaller than a millimeter or less. Barriers meeting this criterion can still, during severe fire exposure, allow flames to appear within the protected volume. This has been observed with some woven fiberglass

barriers. It is probably a result of the barrier itself becoming hot enough to serve as an

ignition source for a flammable gas mixture inside the barrier. If the entire barrier

remains intact in such a circumstance, the burning rate of the materials within the barrier,

limited by air supply rate, will remain low so this form of "failure" may not be

particularly threatening.

Real products such as mattresses, made with barriers, must have seams where edges of

the barrier material are joined together. These seams must serve the same functions as the rest of the barrier and so must be closed with thread that can withstand fire exposure

without allowing the seam to open. Actual practice is somewhat forgiving in this regard,

as indicated below.

Many of the barrier materials currently available are based on organic fibers which char

when heated. Thus it is often a char which serves as the actual barrier between flames

and the vulnerable contents of a mattress (so the insulative properties of the char are important as is its lack of fissuring). Such chars are prone to oxidation during flame

exposure which effectively erodes them, giving the barrier a finite period of protection.

This protection period depends on the nature of the organic fiber, minor contaminants in

the fiber (some metal ions catalyze char oxidation; borates and phosphates can suppress

char oxidation and also, for a fiber like cotton, increase the fraction of the fiber converted

to char), the char mass per unit area and the temperature at which the char is held. This

last condition depends on the heat flux which the charred fiber receives; the higher the

flux, the higher the char temperature and, therefore, the shorter the protection period.

The TB 603 gas burners (like some portions of burning bedclothes) provide high fluxes

which have, however, a relatively short duration, mimicking that of local bedclothes

flames. Most current barriers are designed to withstand this exposure. Crevice flames

provide about half the heat flux but can last much longer (up to 20 min or more). Thus it

is frequently crevice flames, often at mattress corners where they are most intense and

persistent, which ultimately cause barrier failure.

24
Experience indicates that the most threatening type of barrier failure situation is one in

which flames from the exterior reach all the way into some portion of the open cavity

occupied by the springs in either a mattress or a foundation '. Flames on the interior

surfaces of this volume of a mattress are well-insulated and prone to spread, probably at a

rate limited mainly by the air supply rate. Transient heat accumulation within the

mattress interior will also cause the burning rate (and HRR) to grow.

A foundation, subject to the same fire breakthrough into its interior cavity, presents a somewhat different situation. First, its internal fire growth is not limited by air supply;

the bottom of a foundation is virtually open. Fire growth appears to be frequently limited

by the very thin nature of some of the materials (on the sides and the dust cover) which

support only small flames. These flames may spread sporadically and not get an

appreciable fire going on the real fuel sources - the wood base and the top pad. When

these latter materials do burn together, the resulting fire is serious and poses a severe

threat to the mattress as well, since it is directly under it.

In many mattress and foundation designs, it is along the sides that this interior volume is nearest to exterior bedclothes flames. This is why a good side barrier and protected side seams are necessary. The tape edge seams, on the other hand, are somewhat removed

from the spring cavity, typically by compressed layers of foam or other cushioning

material. Experience shows that the tape edge seam does frequently have a tendency to open slightly as the materials it captures shrink or partly melt away. This does amount to providing a hole (actually more of a slit, ca. 2 mm wide, of varying length) in the barrier.

This does not appear to lead rapidly to a growing fire because any flames which enter

encounter foam, perhaps 2 cm to 3 cm or more thick, blocking access to the spring cavity.

Crevice flames, typically quite limited in size, can eventually melt through such a blockage if they persist at one location for many minutes. The overall negative

consequences of such edge seam openings seem to be quite sporadic from one test to the

next, from negligible to serious (a type of binary behavior described above). Among

other things, this could be one path that yields an internal "puff in the mattress that often

leads to a growing fire over the next several minutes.

The above discussion implies that barrier materials must qualify by having both short

term resistance to the high heat flux from the TB 603 gas burners as well as long-term,

low flux resistance to crevice flames. A test for the latter is in development in the context

of mattress material assemblies. In addition, since barrier materials are, at least in some

locations, under tension, they need to have some degree of tensile strength. This is particularly an issue as the barrier is heated and chars since that process can both weaken

the fibers and cause the barrier material to shrink, thereby increasing the tensile stress; the result can be a split. At present, the author is not aware of any available tests for

barrier shrinkage.

'" This does not mean that a soHd foam core mattress is inherently safer. Such a mattress may be subject to other problems such as a melt pool fire on the floor.

25
Qualitative HRR Consequences of Various Barrier Failures. With the above

discussion in mind, we consider how various possible deficiencies in a barrier could be

reflected in the HRR seen during a TB 603 test. The ultimate concern is to infer if they

imply an early and serious fire in a real bed assembly. Generally speaking, it is not

possible to predict the ultimate consequences of barrier deficiencies in any quantitative

manner (i.e., how big the HRR peak will be or exactly when). There are too many

variables affecting these measures. Instead we attempt to estimate qualitatively when and

how the mattress/foundation fire will begin to grow in response to a barrier deficiency.

Experience has shown that there are a number of barriers available that can give quite

good performance in TB 603 and with bedclothes fires; some, however, appear to be

marginally effective. This same experience also suggests that potentially good barriers

are compromised by quality variations leading to either large areas (comparable to the

mattress dimensions) or small areas (several square centimeters) of lessened fire resistance. These two scales of defects have differing implications in TB 603, as discussed below. Similarly, the mattress construction may be at fault, with, for example,

missing sections of barrier material or improper thread in the seams, resulting in localized or global vulnerabilities. Alternatively, the barrier material used may inherently be

marginally adequate in fire resistance, particularly when used in combination with other

mattress design parameters. We want to pursue the probable consequences of these

various shortcomings as seen in the resulting HRR curves.

Case 1 : A good barrier with large scale deficiencies in the sample tested . By assumption,

this case involves a barrier (in the particular sample being tested) which is less than

adequate to pass the TB 603 criteria over most of either the mattress or foundation (or

both) surfaces. Then the chances are high that the burners will be applied to the deficient

area. That makes this case qualitatively the same as one in which the barrier is not

defective but, even when perfect, is marginally adequate for the given mattress design.

The barrier deficiency (or inadequacy) can take several forms including excessive heat

transmission (due to insufficient thickness, an improper blend of fibers or, in the case of

cotton, insufficient char-promoting flame retardant), decreased fire duration resistance

(leading to early burn-through, most likely either where the burner flames strike or in a corner crevice) or increased shrinkage when heated. More than one of these may apply at the same time.

Excessive heat transmission means that material immediately inside the barrier

will be degraded, gasified and burned more extensively than normal resulting in an increased HRR from the start with contributions from all fire-affected surfaces.

Crevice flames will be larger and more persistent, especially if the deficient

barrier is in both the mattress and foundation. The implications for a real

bedroom fire driven by burning bedclothes are worrisome since, in general, the

larger burning area there will mean a larger heat release rate contribution from the

mattress/foundation. Larger and/or more persistent crevice flames in a TB 603

tests also tend to provoke the problem in the next bullet below, i.e., barrier bumthrough.

26
•

Decreased fire duration resistance means an increased probability of barrier burnthrough, usually (but not exclusively) either in the burner application area or at crevice corners. This latter failure location cannot begin to be tested until the

crevice flames reach the corners, often more than 10 to 15 min into a test. A

failure at either location in a TB 603 test will usually let fire into the mattress

interior with the result being a growing fire. A bedclothes fire will, of course,

exploit this type of vulnerability relatively quickly since it will bring flames to the corners quickly (less than 10 min).

Increased shrinkage means there is an enhanced probability that the charred

barrier will break open, probably starting at the burner application area, likely

leading to a growing fire centered there soon after burner application, especially if the affected item is the mattress. Char breakage due to shrinkage is problematic

since it may be dependent on the size of the area being heated. That implies it could be worse (i.e., more likely though no sooner) with a bedclothes fire than

with the burners since they heat a larger area. An implication is that a barrier

which shows such behavior in a burner test is probably not acceptable.

If the large scale defect is the use of a non-fire resistant thread throughout the tape edge

seams, the consequences will be a growing fire from the burner exposure onward, despite

a good barrier material, since the fire will get increasingly into the mattress as the crevice

flames begin to spread and open the seams. A bedclothes fire would produce similar early

mattress fire growth. If the only defect were the use of non-fire resistant thread in

vertical seams, the consequences are similar to Case 2 below.

Case 2: A good barrier with small scale deficiencies in the sample tested. Another

variant of this is local deficiencies in the seams. Here the chances are high that the

burners will not hit the small defective area since it will occur at a random location'.

The good barrier material (or good seam length) will yield a low HRR for a varying

amount of time, depending on how long it takes for the ticking and/or crevice fires to reach the defect zone . Since the defect may see only the ticking fire, it may not be

completely compromised; burning bedclothes would be more likely to fully compromise

such a local defect since they can bring a more intense fire to bear than a ticking fire. Furthermore, on average, burning bedclothes will "find" this defect area sooner than the

ticking/crevice flames (essentially, within 10 min).

Regardless of the type of local deficiency (as laid out above) in a good barrier, the worst

immediate consequence of a local defect is a local hole all the way into the mattress or foundation internal cavity. For a mattress, the good barrier elsewhere will limit the air

'"* A defect on the bottom of the mattress or the top of the foundation would not be found by the post-burner

ticking fire or by a bedclothes fire. Similarly, there is an equal chance it would have no consequences in a

real world fire.

''^ Some combinations of material outside the barrier layer do not sustain flame propagation over the entire exposed mattress/foundation surface. Therefore there is a finite chance the defect will not be revealed in a TB 603 test. A real bed fire is more likely to find most defects on these exposed surfaces.

27
supply to the fire and therefore its size. Such fires, when they occur on top of a mattress,

tend to stay localized with the burning chiefly exterior to the mattress. A hole in the

mattress side can dump more heat into the interior causing some relatively slow fire growth. Such a hole in the foundation can have no effect or a serious longer term effect

depending on whether the hole location includes sufficient fuel to induce top pad and

wood involvement. The consequences with bedclothes are similar but will occur sooner.

Case 3: A marginal barrier with small scale deficiencies in the sample tested. A

marginal barrier is one which just passes the TB 603 criteria. Presumably its marginality

is due to performance in one or more of the three categories laid out under Case 1 above.

Its localized deficiencies may involve areas where its performance is distinctly

inadequate (not just marginal) in these categories or could involve local physical damage

like a cut. Since the deficiency is randomly located, it will again be unlikely to be hit by

the burners and must wait for the slow subsequent flame propagation to reveal it. As in

Case 2 above, the worst immediate consequence of the defect (when it finally is overtaken by ticking or crevice flames) is a hole into the mattress or foundation interior.

Given the marginal character of the rest of the barrier, however, its ability to resist the

intensified flaming around this hole is doubtful. The fire will tend to grow from the hole

outward, possibly getting serious only as it begins to grow synergistically in the mattress

and foundation. The problem will again show up sooner with bedclothes and, given the

impact of the overall added heat and potential additional damage from the bedclothes fire,

the resultant will probably grow faster than in TB 603.

The preceding discussion is necessarily qualitative in nature because there is a continuum

of possible barrier performance levels and deficiencies. We do not have quantitative measures of the relation between barrier characteristics and TB 603 HRR performance.

The common thread in the above discussion is that localized barrier defects and/or overall

barrier marginality usually mean that the observed HRR from a TB 603 test is greater

than that seen from a good, defect-free barrier. While it is impractical to spot barrier

deficiencies directly in tests performed in a room enclosure due to poor visual access, the

above discussion suggests that such deficiencies will usually be reflected in the HRR

behavior being recorded. The increased HRR resulting from global deficiencies occurs immediately both on TB 603 and in complete bed assemblies. Localized barrier

deficiencies show up later in TB 603 than in complete bed assemblies.

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