Capabilities and Limitations of Fire Barriers

Dr. Vytenis BabrauskasFire Science and Technology, Inc.

Question asked by CPSC

• Should CPSC change the regulatory approach from a smolder test on bench-scale models to:– An approach that limits fire growth by

performance requirements similar to 16 CFR 1633?, or

– An approach that requires the use of fire barriers? (for all fabrics, not just Class II fabrics).

Why is CPSC considering changing approach from 16 CFR 1634 (2008 smolder standard)?

• Problems with scaling??

• Difficult to understand this point:– Flaming tests are known not to scale well from

small-scale to large-scale, but cigarette tests do.– California has consistently found that mockups do

predict real-chair behavior.

“Bench scale performance did not predict full scale flammability…especially for smoldering ignition”

Smolder testing…

• CPSC considers that any regulatory test that they adopt needs to accurately control the real-article hazard and classify the products in the same way as they behave in full scale.

• For tested cigarette mockups, CPSC concluded that the mockup tests did not always predict that full-scale chairs will fail by smoldering when cigarettes are placed at certain locations on the chair.

…Smolder testing…

• They identified these problems:– Two different “standard” foams behaved very

differently.– Mockups did not have doubled-over fabric layers

(which promote smolder), while some real furniture did.

– Full-scale furniture itself showed significant differences between supposedly identical samples.

. . . .

…Smolder testing

– Fabric tension may not be well simulated.– Side arms are generally constructed very

differently from back cushions.– Fire barriers, when tested in mockups using

“standard” fabric and “standard” foam do not reproduce the behavior of some actual chairs.

Three possibilities exist

• Require full-scale testing of chairs.– Full-scale testing does not seem practicable, since

there is an enormous number of fabrics used by most manufacturers.

• Stop all standard development • Fix mockup problems…

Improving mockup testing…

• Specifications for “standard” foam have not been adequate. – It is unreasonable to suppose that density, ILD,

permeability, etc. would suffice to describe the smolder propensity.

– It should be possible to define specifications for a “standard” foam, but the specifications must include a cigarette test.

– Smoldering is a chemical phenomenon, and physical tests do not measure chemical properties.

…Improving mockup testing…

• Lack of stringency concerning doubled-up fabrics is simple to fix.– Make mockups use doubled-up fabric.

• Specimen-to-specimen variations in full-scale chair construction.– Have to accept this. Upholstered furniture is hand-

built and not made on an assembly line.

…Improving mockup testing

• Wide differences in construction of real chairs, depending on the exact locale.– Need to select a near-worst-case mockup

configuration. Then most actual variations will tend to give conservative differences, while the few opposite results will be rare.

• Some smolder barriers behave too well in mockup tests, compared to real furniture.– May need to revisit specifications for “standard”

fabric and foam.

Recommendations

• Needed improvements in mockup testing for smolder resistance should not be difficult.– With such modifications, a smolder standard

should prove to be reliable.• I do NOT believe that flame-resistance testing

for barriers is economically justifiable. • I do NOT believe that HRR testing of full-scale

furniture is economically justifiable.

Flame tests or HRR tests are not justified…

• CPSC reported that there are about 30 “addressable” fire deaths per year from small-flame ignitions.

• Added costs would have to be very small to create a positive benefit/cost situation.

• Economic and engineering analyses on large-flame ignitions are non-existent.

• Added costs of producing TB133-type furniture would be large.

• Comfort and choice would be reduced if TB133-type furniture were mandated.

…Flame tests or HRR tests are not justified

• Testing to a peak-HRR type requirement would involve high costs.

• A manufacturer may offer thousands of fabric variations.

• Peak HRR is dependent on fabric type– Babrauskas (1983) showed a factor-of-4 effect!

• Could not adopt the 16 CFR 1633 strategy of ignoring fabric variations.