6 STORAGE OF SPECIAL COMMODITIES AND
6.2 Nonwoven roll goods .1 COMMODITY DESCRIPTION
A nonwoven material is defined as a fabric-like matting of natural or synthetic fibers held together by chemical, mechanical, or thermal bonding. The most common fibers are polypropy-lene, polyester, rayon, polyethypolypropy-lene, cellulose/wood pulp, cotton, and nylon. Chemical binding is achieved with polymers such as acrylics or vinyl acetate copolymers. Mechanical binding is achieved by entangling the fibers with needlepunches, air jets, or water jets. Thermal bonding is applicable to thermoplastic fibers that can be melted and solidified while entwined. Figure 6.5 is a micrograph showing the polyethylene fibers in a thermally bonded nonwoven. The nonwoven trade association’s Nonwoven Fabrics Handbook provides an extensive description of nonwoven, materials, manufacturing processes, and current applications.
Nonwoven fabrics are made and stored on hollow core roles similar to those for roll paper.
Roll sizes and storage modes are similar to roll paper for most fibers. The exceptions are the soft, high-loft nonwovens which often are stored on racks or in pyramid piles on floor.
Nonwoven fabrics are manufactured by paper companies, chemical companies, and textile companies, as well as some independent companies devoted to nonwovens. They are used in a wide variety of products including baby diapers, feminine hygiene products, medical and hospi-tal disposables, industrial and household wipes, mailing envelopes, blanket insulation, wearing apparel linings, carpet backing, house wraps and roofing material, air conditioning filters, and interior automotive trim.
Figure 6.5. Micrograph of a polyethylene nonwoven fabric construction (from www.Tyvek.com)
Nonwoven materials are capable of rapid flame spread and high heat release rates because their fibrous construction allows air access and relatively low thermal inertia (as represented by the product of thermal conductivity, density, and specific heat). Storage as on-end rolls promotes outer layer unwinding and exposure of unburned layers as in roll paper. Thermoplastic nonwovens pose special flame spread problems because of their propensity to melt when they burn.
6.2.2 LOSS EXPERIENCE
Until recently, nonwoven roll goods have not been present in sufficient quantity to be responsible for many fires. The fires that have been reported to date have primarily occurred in cartoned storage of relatively small rolls. Dense smoke in these fires hampered manual firefighting efforts.
One fire involving 15 ft high palletized and rack storage of cartoned polyester and rayon rolls damaged the roof deck and opened 37 ceiling sprinklers (FM loss 72-2970).
6.2.3 FIRE TESTS
Fire products collector tests
Fire Products collector tests have recently been conducted with both on floor storage and on rack storage of nonwoven rolls. The on-floor storage configuration was identical to that of 42 in roll paper (see Figure 6.1). The rack storage configuration consisted of a 2 pallet wide, 2 pallet deep, 2 tier high configuration identical to that used in the Fire Products Collector commodity classi-fication tests described in Chapter 5. Both free burn and water application tests were conducted with both storage configurations.
Nonwovens tested under the Fire Products Collector during a Factory Mutual Research project are listed in Table 6.4. Rolls of thermally bonded (spunbond) polypropylene with basis weights ranging from 20 g/m2 (4.1 lb per 1000 ft2) to 60 g/m2 (12 lb/1000 ft2) were tested, as well as a polypropylene-wood pulp blend (65% wood pulp) with a basis weight of 190 g/m2.
The Roll Loft Factor (RLF) values listed in Table 6.3 are defined as follows:
RLF =
Table 6.4. Nonwoven and roll papers tested used in FMRC fire products collector tests
Fiber Binder Basis weight
(g/m2)
Roll loft factor Heat of combustion (kJ/g)
Polypropylene Spunbond 20 – 26 3 – 4 45
Polypropylene Spunbond 35 2.8 45
Polypropylene Spunbond 57 – 60 2.5 45
Polypropylene Spunbond 25 3.7 45
Cellulose-65%
Polypropylene-35%
Spunbond 190 16.6 28
Polyester Acrylic (15%) 85 94.2 23
Rayon Acrylic (30%) 22 4.0 18.8
Tissue – 17 4.7 16
Tissue – 38 3.8 16
Newsprint – 49 3.8 19
Where L= roll length, D0= roll outer diameter, Di = roll inner (core) diameter, W0= roll weight, Wc = core weight, ρi = bulk density of the ith component, and, mi= mass fraction of the ith component.
Since the roll consists of fuel plus air,
RLF = (Vfuel+ Vair)
Vfuel − 1 = Vair
Vfuel
In other words, RLF is equal to the air/fuel ratio of the roll. Rolls with high values of RLF (nominally greater than 25 per Factory Mutual Data Sheet 8-23) are termed high-loft nonwovens.
They are typically used as batting and fiberfill insulation. Since they have a high air/fuel ratio, they are expected to burn efficiently and completely.
The on-floor free burn heat release rate curves for several nonwovens are shown in Figure 6.5, along with the three roll papers listed in Table 6.4. The curve labeled Coform in Figure 6.5 refers to the cellulose-polypropylene blend with a Roll Loft Factor of 17. Its free burn heat release rate history is very similar to the curves for newsprint and tissue, i.e. rapid fire development with the convective heat release rate increasing to 4 MW about 12 seconds after ignition. The lightweight (22 g/m2) rayon-acrylic nonwoven had an even more rapid fire-growth rate, reaching 4 MW in about six seconds. The on-floor tests with the polypropylene nonwoven showed a much slower fire development accompanied by unraveling of the outer layers of the roll, and polypropylene dripping before burning.
Newsprint (10.0 lb/1000 ft2)
0
Convective heat release rate (kW) Convective heat release rate (1000 Btu/min)
60 80 100
Figure 6.6. Paper and nonwoven roll heat release rates.2002 Factory Mutual Insurance Company, with permission
The water application test results for the polypropylene-wood pulp were also similar to the data for the roll papers tested, with only small reductions in peak heat release rate at the discharge den-sities used. This is in contrast to the polypropylene spunbond, which did experience melt burning but at a rate that was easily controlled with water delivered densities as low as 0.14 gpm/ft2.
Polypropylene melting was a far greater problem in the on-rack tests. The different basis weight polypropylene spunbonds required five to six minutes to become fully involved. However, the peak convective heat release rates for the polypropylene spunbonds were much larger than those of any of the roll papers (it exceeded the 10 MW capacity of the Fire Products Collector) with and without water application.
Sprinklered fire tests
Sprinklered fire tests have confirmed that nonwoven rolls are extremely difficult to protect effectively. Rack storage tests with high-loft polyester batting protected by K= 11 gpm/psi1/2 sprinklers discharging 1.0 gpm/ft2 resulted in complete burn out of the intermediate-scale array.
Thus ceiling sprinklers need to be supplemented by in-rack sprinklers. Rack storage tests with in-rack sprinklers in the longitudinal flue and rack face (aisle) were able to provide effective protection for polypropylene nonwovens.
Nonwoven roll on-floor storage is even more of a challenge than rack storage because of the need to rely on ceiling sprinklers only. The author is aware of only one on-floor nonwoven roll test in which the fire was controlled. That particular test involved 21 ft high storage of a polyester-rayon 50/50 blend with a low roll loft factor. ESFR sprinklers discharging 100 gpm for each 100 ft2 of sprinkler coverage did limit fire spread; but 12 sprinklers opened. Since this is more than were opened in any of the rack storage tests with the prototype Group A plastic commodity under a 30 ft high ceiling, the installation guidelines based on early suppression of the standard plastic commodity tests are not applicable.
The uncontrolled fire tests with on-floor storage involved a 50% polyester – 50% rayon nonwoven, and the following nonwovens listed in Table 6.4: spunbound polypropylene, polyester-acrylic, and rayon-acrylic. Water flow rates per sprinkler were in the range 60 – 105 gpm, corresponding to discharge densities of 0.60 – 1.05 gpm/ft2. Two tests were conducted with K = 7.8 gpm/(psig)0.5 sprinklers, and three tests were conducted with large drop sprinklers (K = 11 gpm/(psig)0.5). Storage heights varied from 15 – 20 ft high under a 30 ft ceiling.
6.2.4 SPRINKLER PROTECTION REQUIREMENTS FOR NONWOVENS
Guidelines for sprinkler protection of nonwoven roll storage are provided in FM Data Sheet 8-23.
In the case of on-floor storage, the lack of success with the 10 – 15 ft clearances in the fire tests, motivated recommendations for false ceilings in order to avoid these clearances above nonwoven stacks in a warehouse. Even with these low clearances, large demand areas (as much as 5000 ft2) are recommended for on-floor storage.
Rack storage protection specifications in FM Data Sheet 8-23 include options for either using combined flue and face in-rack sprinklers, or a mid-height barrier in conjunction with face sprinklers. Adjustments to these recommendations are expected as additional test data and loss experience is acquired.