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Battelle Memorial Institute and Underwriters Laboratories do not condone or endorse the use of propane cylinders indoors beyond those limited cases currently authorized by NFPA 58.

SUPPLEMENT 3

Fire Testing of Composite Propane Cylinders

Editor’s Note: This supplement provides information on the testing of composite cylin-ders. These tests were funded by the Propane Education and Research Council to support the proposal to allow portable heaters fueled by a composite cylinder (cabinet heaters) in buildings. The proposal has not been accepted, but may be considered for a future edition of NFPA 58. Currently, cabinet heaters can be used if a public emergency is declared, such as a hurricane or ice storm. The results of the testing showed that composite cylin-ders act very differently from steel cylinders in simulated room fires, and the supplement is intended to communicate the test results to anyone interested in this subject.

The editor thanks Rodney L. Osborne, Ph.D., P.E, of Battelle Memorial Institute, and Pravinray D. Gandhi, Ph.D., P.E., and Ronald R. Czischke, P.E., of Underwriters Labora-tories Inc., who authored this supplement.

INTRODUCTION

Composite propane cylinders have been used in Europe for about 15 years and have recently entered the United States market for the storage, handling, and use of propane gas. In 2007, two manufacturers were marketing cylinders with nominal capacities of 10 lb, 20 lb, and 33 lb. These cylin-ders were imported into or manufactured in the United States under special permits from the U.S. Department of Transportation (DOT). The DOT-specified tests in these permits subject the cylinders to high temperature creep, gas permeability, vertical drop, pressure cycling, hydraulic burst, gunfire, and bonfire.

Composite cylinder manufacturers had performed vari-ous tests on their cylinders to meet European and U.S. stan-dards. However, it was recognized that more comprehensive fire testing was needed to independently generate the data needed on the cylinders’ fire performance. The test protocol and results obtained are described in this supplement.

COMPOSITE CYLINDER BACKGROUND

Users may choose composite cylinders for outdoor con-sumer applications such as grills, patio heaters, patio light-

ing, and similar appliances, or in industrial or commercial applications where steel and aluminum cylinders are being used. The composite cylinders offer several advantages over steel cylinders in that they weigh less and are corro-sion resistant. In addition, composite cylinders have trans-lucent walls that make the liquid level visible. No external devices or stickers are required to determine the amount of propane remaining in the cylinder.

FIRE TEST PROGRAMS

Two test programs were developed to determine the fire performance characteristics of outdoor composite propane cylinder use and the potential consequences of bringing these cylinders indoors. NFPA 58 currently prohibits bring-ing these cylinders indoors except in very limited cases. Composite cylinders from two manufacturers were used in each of the test programs. One design was a single piece construction, and the other was a two-piece construction.

Outdoor Fire Testing Program

In the first program, Battelle Memorial Institute (Columbus, Ohio) and ThermDyne Technologies Limited (Kingston,

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Ontario, Canada) developed a protocol to test the cylin-ders’ performance with respect to the fire exposure inten-sity, liquid fill levels, and cylinder orientations. Twenty-nine composite cylinders from two manufacturers and six stan-dard steel cylinders were exposed to propane torch fires (Exhibit S3.1). The total heat release rate of the torches was approximately 540 kW (1,800,000 Btu/hr). The cylin-ders were placed at a fixed distance from the face of the torches. All cylinders were nominal 20 lb capacity (0.32 ft3 or 45 to 47 lb water capacity). In this first round of testing, the cylinders were oriented either vertically (Exhibit S3.2) or horizontally (Exhibit S3.3). In the horizontal position, the flame was directed at the side (as shown in Exhibit S3.3), at the valve, or at the base for the different tests. The propane torches were shut down after all the propane

from a test cylinder was vented or when a test cylinder ruptured.

No steel cylinders ruptured during the testing. The relief valves opened at pressures between 375 to 400 psig. Some relief valves reclosed above 300 psig, and some did not reclose until 100 psig. In all tests, the steel cylinders emptied before the cylinder walls softened and thinned enough to rupture. One steel cylinder bulged during the test.

When tested vertically and with a nominal fill level of 75 percent, the two composite cylinder designs did not fail. During these tests, propane began to leak around the valve-cylinder connection and diffused through the cylinder walls after reaching peak pressures between 98 and 118 psig. Exhibit S3.4 shows that the propane continues to

EXHIBIT S3.1 Propane Torches for Fire Exposure.

EXHIBIT S3.2 Vertical Cylinder Prior to Flame Impingement.

EXHIBIT S3.3 Horizontal Cylinder Prior to Flame Impingement.

EXHIBIT S3.4 Vertical Cylinder During Fire Test.

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are combustible, these data can be used by fire protection engineers in considering storage requirements of empty cylinders. Maximum heat release rates ranged from 98 to 119 kW for the two manufacturers’ cylinders. The maxi-mum smoke release rates were 0.65 m3/sec for cylinders from one manufacturer and 2.65 m3/sec for the other man-ufacturer’s cylinders.

In the next set of tests (referred to as Type 2 tests), a composite cylinder was tested with a space heater as a potential future application using an NFPA 286[1] config-uration test room with the cylinder exposed to a standard igniter (see Exhibit S3.5 for a schematic of the test room). (As noted, NFPA 58 currently prohibits this application.) In this test, the test room was lined with gypsum wall-board. The heater with cylinder was located in the corner facing the open doorway. In one test, an additional spare cylinder, positioned next to the heater, was exposed to the igniter. The increase in temperatures and heat flux in the test room, as well as pressure in the gas cylinder were measured. The cylinders were ignited in the same manner as the Type 1 tests.

permeate through the wall even though the cylinder pres-sure is essentially zero. The outer protective jacket was consumed on all composite cylinder tests.

When one of the composite cylinder designs (two- piece construction) was tested in the horizontal position, the cylinder ruptured. This failure was repeatable. The same result occurred with this cylinder design in the verti-cal position and a low fill level. Under similar conditions, the other cylinder design did not rupture.

Twenty of the 29 composite cylinders had pressure relief valves, integral to the cylinder valve. Only one of the relief valves opened, on a test where the cylinder was horizontal and the flame was aimed directly at the valve. The peak pressure for this test was 112 psig. It is suspected that the elastomers in the relief valve degraded and the valve opened. There was no appreciable difference in per-formance between the cylinders that had relief valves and those that did not.

Indoor Fire Testing Program

In the second test program, a performance test plan was developed to consider the potential consequences of bring-ing composite cylinders indoors and was based on input from the propane industry and fire protection community. Battelle and Underwriters Laboratories Inc. (UL) devel-oped this fire test plan and performed the testing in UL’s large-scale fire test facility in Northbrook, Illinois (see http://www.ul.com/fire/research.html).

The test plan was designed to address various fire safety concerns, such as the following:

● Fire hazard from an empty stored cylinder ● Contribution of potential leaking gas from a compos-

ite cylinder to fire hazards in a room fire ● Possibility of a composite cylinder rupture when ex-

posed to an ignition source ● Contribution to room fires from a spare composite

cylinder stored indoors ● Effects of fire hose spray on a burning composite

cylinder

Composite cylinders from the same two manufactur-ers (single piece and two piece constructions) were used in this second phase of fire testing. No steel cylinders were tested in this phase.

The first set of tests (referred to as Type 1 tests) con-sidered the smoke and heat released from ignited empty composite cylinders. These cylinders were ignited by plac-ing an igniter (a cotton bundle soaked in gasoline) at the base of the cylinder. The heat and smoke release rates of the empty, burning composite cylinders were measured. As the jackets and the resins used in the composite cylinders

The heater that was used in these tests was essentially a sheet metal enclosure, with air vents at the top and bot-tom that included a heating element, controls, and space for the propane composite cylinder.

For these tests, except for the test involving a spare cylinder, the cylinder pressure increased during the tests until propane gas began to release after 4 to 12 minutes, at

8 ft

8 ft

12 ft

TC 1

TC 2

TC 5 TC 6

TC 4

TC 7

TC 3

80 in.

30 in.

Igniter inside

Heater with propane cylinder

Flux meter

Paper targets

Front

EXHIBIT S3.5 Schematic of Fire Test Room – Type 2 Tests.

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a pressure level from 163 to 242 psig. The release of gas did not result in high velocity flame jets such as through a relief valve orifice. The released gas was consumed in the fire.

When gas was released, the heat flux (measured on the center of the floor) and the room temperature (measured below the ceiling) increased very quickly. The average ceiling temperatures reached 614°C to 831°C. The maxi-mum heat flux obtained was 20 to36 kW/m2.

For all tests involving ignition of a full cylinder in the heater, the room reached (or was close to) flashover condi-tions between 5 to 12 minutes after ignition. As a general guideline, flashover with flames coming out through the doorway occur in a NFPA 286 room in the same time pe-riod as the crumpled paper targets ignite, the ceiling tem-perature reaches approximately 600°C, and the heat flux level on the floor reaches approximately 20 kW/m2.

Once the cylinder began venting, it continued to re-lease gas. In the test scenarios, the released gas was con-sumed in the fire. The cylinder was emptied approximately 10 to 15 minutes after the maximum pressure was reached. All cylinders showed areas were the resin was consumed at such an extent that gas could easily pass through. The photos in Exhibit S3.6 are representative of composite cylinders after the propane in the cylinder was consumed and the fire was extinguished. The photos show that the cylinder jackets were consumed, as was much of the resin in the cylinder walls.

In one of the Type 2 tests, a rupture occurred 17 min-utes into the test, at a pressure of 46 psig. The rupture oc-curred when the pressure level was decaying, 8 minutes after the pressure had reached its maximum level of 243 psig. The burst resulted in severe heater and room damage. The failed cylinder was the same design (two piece construc-tion) that ruptured during the first fire test program.

In the test with the spare cylinder, the burning rate of the cylinder surface was lower and the increase in cylinder pressure was slower, than for a cylinder located in a heater. The spare cylinder did not release gas throughout the test, reaching 303 psig at the test termination time of 20 min-utes. The fire size of the burning spare cylinder did not result in any significant pressure increase or visible dam-age of the cylinder in the heater.

In the third set of tests (referred to as Type 3 tests), the fire performance of a heater with composite propane cylin-der was assessed in a room fire scenario that grows to flashover conditions. In this test, the test room was lined with medium density fiberboard (see Exhibit S3.7 for a schematic of the test room). A heater with a composite propane cylinder was positioned against the wall facing the open doorway. A 300 kW or a 40 to 160 kW propane burner located in the corner of the room was used to ignite

EXHIBIT S3.6 Composite Cylinder After Fire Test, Shown Inside Heater (top) and Composite Cylinder After Fire Test (bottom).

8 ft

8 ft

12 ft

TC 1

TC 2

TC 5 TC 6

TC 4

TC 7

TC 3

80 in.

30 in.

Heater with propane cylinder

Sand burner

Paper targets

Front

EXHIBIT S3.7 Schematic of the Fire Test Room – Type 3 Tests.

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cylinder, filled to half of its capacity with water, which was pressurized by nitrogen following a predetermined cylin-der pressure-time curve obtained in Type 2 tests. The cyl-inder was impacted by a water hose stream when a cylinder pressure of 220 psig was reached, 6 minutes into the test. The water hose stream was generated from an Elkhart SLO/0 adjustable nozzle on a 11⁄2 in. rubber hose. The ad-justable nozzle was set at maximum flow and a straight stream. The available water pressure to the hose was a nominal 100 psig. The stream was aimed directly at the cylinder from a distance of approximately 18 ft. The cylin-der breached before the hose stream impact. However, the hose stream impact did not cause additional damage to the cylinder.

Testing Summary

The key findings of the second test program were the fol-lowing:

1. Fire hazard from empty or filled stored cylinder

a. The maximum heat release rates from the ignition and burning of the empty cylinders were approxi-mately 100 to120 kW.

b. A full stored cylinder sustained the radiant heat from a 300 kW fire for 20 minutes without being ignited or leaking propane (Type 3).

c. A burning, nitrogen-pressurized stored cylinder did not violently breach or rupture when impacted with a water hose stream.

2. Contribution of leaking gas from an ignited cylinder to fire hazards in a room fire

a. In each of the fire tests (Type 2), the ignited com-posite cylinder in the heater assembly released gas resulting in flashover conditions in the room.

b. In a growing room fire that goes to flashover (Type 3), the composite cylinder breached and ignited after the flashover had occurred. Typi-cally, there was a 3 to 5 minute lag between room flashover and breach of the cylinder. The leaking gas cylinder did not rupture.

c. Once the cylinder started to leak, the release of gas continued during the test. A full cylinder was emptied approximately 10 to 15 minutes after the maximum pressure was reached.

3. Rupture hazard from propane filled cylinder:

a. Cylinder design played a role in its fire perfor-mance. The design from one manufacturer with the two piece construction ruptured when partially filled and oriented horizontally during a Type 2 test.

the medium density fiberboard, resulting in flashover con-ditions in the test room. In one test, an additional spare cylinder was positioned next to the heater. The increases in temperatures, ensuing from the fire growth, were measured and the performance of the heater with a composite cylin-der was assessed.

The room reached flashover conditions after 1 to 2 minutes for the 300 kW initial burner size and after 4 to 7 minutes for the 40 kW/160 kW burner size, but the cylin-der in the heater was not immediately affected. It was ob-served that the gas pressure peak and subsequent release of propane gas occurred 3 to 6 minutes after the room reached flashover conditions. The cylinders did not rupture or re-lease gas in any high velocity jet–like fashion outside of the heater. The released gas was consumed in the fire. The release of propane gas occurred after 6 to 12 minutes, at a pressure level of 170 to 270 psig. At the conclusion of the test, the cylinders in general showed the same type of dam-age as in the Type 2 tests.

In the Type 3 test with a spare cylinder and a cylinder in the heater, both cylinders sustained the radiant heat from a 300 kW fire for 20 minutes without igniting or leaking propane. The spare cylinder pressure increased to 231 psig, and the pressure of the cylinder in the heater increased to 123 psig, during the 30 minute test. Exhibit S3.8 shows the exterior of the spare cylinder after this test, with the jacket partially melted, but with no significant damage to the pressure vessel walls.

The final test at UL was to assess the performance of a burning pressurized cylinder when impacted by a water hose stream. Two igniters were attached to a composite

EXHIBIT S3.8 Spare Cylinder After Fire Test.

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4. High velocity jetting of propane gas flames upon leak-age from the cylinder

a. In all the Type 2 and Type 3 tests, there was no evidence of high velocity jetting of propane gas after the composite cylinder had breached and ig-nited. The cylinder pressure when the breach was observed (128 to 270 psig) was lower than the re-lief valve setting (375 psig).

The full test reports are available from the Propane Educa-tion & Research Council (Washington, DC) at www.propanecouncil.org (reference Research Docket No. 11643).

REFERENCE CITED

1. NFPA 286, Standard Methods of Fire Tests for Evalu-ating Contribution of Wall and Ceiling Interior Finish to Room Fire Growth, 2006 edition, National Fire Pro-tection Association, Quincy, MA.