Process Safety Progress (Vol.21, No.2) June 2002 85

An alternative methodology to that of United Nations,Appendix 5, Sample Method, has been developed by theO rganic Peroxides Producers Safety Division of the Societyof the Plastics Industry (OPPSD/SPI) to assure the safe emer-gency venting of organic peroxides in an approved contain-e r. The methodology is applicable for designing a new con-tainer for an existing or new organic peroxide. Bench-scaletesting with a 10 liter vessel determined the maximum pre s-s u re pulse (spike) generated during a thermal decomposi-t i o n / o v e r p ressurization vs. the ultimate, structural stre n g t hof the container measured and/or calculated. The methodol-ogy has been tested full scale with a United Nations 6(c) fuelf i re. Container deformation, so long as there is no fragmen-tation, is permitted with the proviso that the container beretired from service following an incident. The methodology,as developed, reflects advances in technology while “harm o-nizing” to a maximum extent with the United Nations,Appendix 5, Sample Method.

I N T R O D U C T I O NOn December 11, 1990, heavy fog conditions along

a Tennessee Interstate Highway caused a multiple carand truck accident. In all, 75 vehicles were involved.By chance, the resultant ruptured fuel tank fire sengulfed a tractor-trailer transporting ten (10) GEOSpecialty Chemicals, (formerly Hercules, Inc.), D.O.T.Spec. 57 containers of dicumyl peroxide. In the ensu-ing fire, the 421 gallon containers, each containing3,500 pounds of the organic peroxide, underwentthermal decomposition and overpressurization.

Subsequent investigations, which included metal-l u rgical examinations of the containers, determ i n e dthat all ten had vented the organic peroxide decom-position products successfully without loss of structur-al integrity, breach, or fragmentation. It was alsod e t e rmined that the GEO container had been heavily

overdesigned. They were fitted with a 22.5 inch diam-eter frangible disk with an integral three inch diame-ter relief device designed to melt at 300° F, thus pro-viding early pre s s u re release before the primary re l i e fdevice was engaged.

This real-life incident, while successful, raised cer-tain questions concerning the expected perf o rm a n c eof other peroxides in approved containers. As a result,the O rganic Peroxides Producers Safety Division of theSociety of the Plastics Industry (OPPSD/SPI) developed amethodology to evaluate the safety and suitability of agiven container for transporting a specific organic per-oxide, to preclude the possibility of container failuref rom overpressurization which could result in frag-mentation. Bench-scale and full-scale tests sponsore dby the OPPSD/SPI validated the method.

A P P R O A C H• Design and fabricate a high-pre s s u re, bench-scale,

10 liter, test vessel that can safely withstand multi-ple tests and overpressurizations.

• Conduct thermal decomposition/overpre s s u r i z a-tion tests to develop and verify reproducibility of astandard operating procedure.

• Select a standard organic peroxide for subsequenttesting.

• Verify traditional literature relationship of decom-position pre s s u re pulse (spike) vs. the ratio vent-ing relief area to working-heated volume (A/V).

• Identify the maximum pre s s u re pulse for the stan-d a rd organic peroxide and extrapolate response toan approved commercial container.

• D e t e rmine, by testing and mathematical methods,the ultimate structural strength of the full-scalecommercial container.

An Example of a Test Method forVent Sizing—OPPSD/SPI Methodology

Charles S. Poteet III a and Marvin L. Banks ba Peroxy Engineering Specialist, GEO Specialty Chemicals, Peroxy Chemicals Group, 50 N. Market Street, Gibbstown, NJ 08027b Program Manager, Hazards Testing, Energetic Materials Research and Testing Center, New Mexico Institute of Mining andTechnology, Campus Station, Socorro, NM 87801

• Conduct a full-scale United Nations 6(c) Fuel Fireand evaluate the applicability of the bench-scalemethod for predicting results.

• P resent the methodology for the determination ofthe suitability of a specific organic peroxide for ana p p roved container, and conversely, the design ofa new container for an existing or new org a n i cperoxide.

BENCH-SCALE - 10 LITER SUPPORT STUDIES

Test SiteThe 10 liter test apparatus was set up at the “Little

Eagle” explosion-proof bunker of the Energetic Mate-rials Research and Testing Center at New Mexico Insti-tute of Mining & Technology (EMRTC/NMT) in Socor-ro, New Mexico. Tests were witnessed by OPPSD/SPIpersonnel. A video system permitted real-time moni-toring of the tests’ pro g ress during overpre s s u r i z a t i o nand subsequent venting. Pre s s u re and temperaturetelemetry was sent to a remote location for acquisitionand analysis. Results, along with descriptions of testapparatus and pro c e d u res are contained inEMRTC/NMT Report FR-98-07.

Test Apparatus Test Ve s s e l . (See Figure 1b) A 10 liter cylindrical

vessel was constructed with an 8 inch internal diame-ter stainless steel pipe having a wall thickness of 1inch. The base plate and top plate were cut from a 1inch thick stainless steel plate. An 0.5 inch stainlesssteel plate was welded into the bottom of the pipe,and an O-ring was installed at the top of the pipe tocomplete the pre s s u re vessel. The vessel is boltedtogether with six 0.625 inch bolts of number 8 hard-ness. The pressure rating for the vessel was calculatedat 2,500 psig.

H e a t e r s . Sixteen 0.5 inch diameter heater wellsw e re drilled into the walls to a depth of 11 inchesf rom the bottom. Eight 2,000 watt cartridge heaters( Watlow J10A64-D12H) and eight 1,500 watt cartridgeheaters (Watlow J10A33-D12H) were installed usingA/B/A/B pattern. An 0.125 inch diameter, 3,000 watt“cable” heater was spiral wound in the 0.25 inchspace between the welded bottom and the 1 inchthick base plate. Because the 240 volt heaters wererun using 208 volts, the total heater power was nomi-nally 23,250 watts (21,000 watts in the walls and 2,250watts on the bottom). Two layers of ceramic fiberinsulation were wrapped around the side and bottomof the vessel.

T h e rmocouples. T h ree 0.063 inch diameter K-Ty p e ,stainless steel sheathed, ungrounded therm o c o u p l e s(Omega Engineering, Inc., CASS-116-U-12) were usedto measure the temperatures inside the vessel. Onethermocouple was located inside the vapor phase, thesecond was 0.5 inches below the surface of the liquid,and the third was located 1.5 inches from the bottom.The thermocouples were installed as shown in Figure1 utilizing Swagelok® fittings. Omega SA1-K stick-onK - Type thermocouples were used on the outside andbottom walls of the vessel to control the heaters.

R u p t u re Disks & Orifice Plates. The Type P rupturedisks had a burst pre s s u re of 20 psig at 90° C andw e re purchased from the Fike Corporation. Elevatedt e m p e r a t u res have very little effect on the burst pre s-s u re. Burst pre s s u res from 21 to 23 psig wereobserved. The holder assembly was Type G, boltedstyle, 15-# RF, CS/CS with an open throat. The top ringof the assembly was 0.5 inches larger than the rupturedisk diameter.

Orifice plates were machined from 0.25 inch thickstainless steel plate and machined to varying orificediameters. Diameters range from 0.75 to 4.0 inches in0.25 inch increments.

Load Cell. An Omega Engineering, Inc., LCDA-150Load Cell was used to re c o rd the rate of material lossf rom the apparatus. Although the load cell had acapacity of 150 pounds, the fixture was mounted on afulcrum arrangement, which allowed for a total loadcapacity of 300 pounds. The load cell and fulcrumwere installed as depicted in Figure 1b.

P re s s u re Measure m e n t s . Two Setra Model 280Evariable capacitance transducers were used to obtainp re s s u re data. They were connected to the vesselusing 14 inches of 0.25 inch outer diameter stainlesssteel tubing, as depicted in Figure 1b. The manufactur-e r ’ s listed response time for the Model 280E is onemillisecond. Each transducer was ported to a separatecomputer system, reducing the possibility of data loss.

Test Procedures Vessel Te m p e r a t u re Contro l . The heaters were con-

t rolled using a Pentium® desktop computer with aStrawberry Tree, Inc., Model ACPC-12-8 Analog/Digi-tal I/O board. Thermocouple signals from the vesselwall were re c o rded and used to control a 12 volt DCcontrol signal from the computer to switch the heaterson and off. This signal was connected to six OmegaEngineering, Inc., 240v 45a solid-state relays to controlthe 208 volt AC directed to the heaters. The systemsample rate of 12 measurements per second was morethan adequate.

P re s s u re Data Collection. The signal from one of thep re s s u re transducers was fed to a Strawberry Tree, Inc.,D y n a res 8-channel Analog/Digital I/O board installedin a Pentium Computer. This system was pro g r a m m e dto collect data at 1 KHz, which matched the re s p o n s etime of the transducer. Because of the high sample rate,the system was run at 12 bit resolution. In order to limitthe size of the data file, this system was activated assoon as the rupture disk had burst and was shut down afew minutes after the reaction. This method of opera-tion limited the amount of data collected, but retained ap rofile of the high-pre s s u re pulse.

P re s s u re, Te m p e r a t u re & Load Cell Data Collection.The liquid and vapor temperatures inside the vessel,the second pre s s u re transducer, and the load cell dataw e re re c o rded using a third Pentium computer and aD y n a res 8-channel Analog/Digital I/O board fro mStrawberry Tree, Inc. The sampling rate of this systemwas set at 100 Hz. In order to maintain this samplerate, the pre s s u re and load cell signals were re c o rd e das voltages. The temperatures were converted by thesoftware to the actual temperatures.

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Process Safety Progress (Vol.21, No.2) June 2002 87

P ro c e d u r a l. The test vessel was preheated to justabove the storage temperature listed in the MSDS forthe material before loading. The 10 liter volume vesselwas filled with 9.0 liters of the sample material, 99.7%dicumyl peroxide.

The internal temperature ramp rate was set at 6° C/min/min, the calculated American Petroleum Insti-tute’s API 520/521 heat-up rate for a United Nations 6(c)fuel fire re g a rded as the worst case scenario for an org a n-ic peroxide shipping container.

The rupture disk was installed to seal the vessel, andheating was begun within 10 minutes. Both the heaterc o n t rol and the data collection computers were startedsimultaneously, and the fast data collection computerwas started when the rupture disk failed. The heatersw e re run at the designated ramp rate until several min-utes after the decomposition reaction had occurred.

A video re c o rding system allowed monitoring ofthe test’s pro g ress. An explosion-proof fan was usedto remove residual vapors prior to personnel re-entry.

10 LITER TEST RESULT S

Temperature Ramp Rate vs. Peak Pressure PulseIt is commonly accepted in the literature that the

Peak Pressure Pulse from an organic peroxide decom-position and vessel overpressurization is dependenton, and can be correlated with, the heating rate ort e m p e r a t u re ramp rate of the material being tested fora constant venting area to working-heated volumeratio. There f o re, this relationship was investigatedfirst. A 2.25 inch diameter disk was set as a constant.This yields a 1.67 inch2/gallon ratio of venting area to

Figures 1a and b. 10 liter vessels for venting tests.

working-heated volume, or 0.60 gal lons/inch2,depending on pre f e r red method of stating the ratio,A/V vs. V/A. Dicumyl peroxide was the test material.Table 1 presents the results for four ramp rates; 2°, 6°,9°, and 23° C per minute per minute with replicates.

When graphed (Figure 2), the relationship is seenas near-linear, confirming the assumption and demon-strating reproducibility.

Peak Pressure Pulse vs. Venting Area to WorkingVolume Ratio

Next, the investigation turned to determining therelationship of peak pressure pulse (spike) vs. ventinga rea to working-heated volume ratio (A/V) with thet e m p e r a t u re ramp rate set constant at 6° C/min/min.This is the calculated API 520/521 heat-up or ramprate for a fuel fire and is currently recognized by theUnited Nations in a U.N. 6 (c) full-scale burning test.Five disk or orifice size diameters were selected; 3.00,2.25, 2.00, 1.75, and 1.5 inches, to bracket the equiva-

lent frangible disk size on a D.O.T. Spec. 57 GEOSpecialty Chemicals container. Results are pre s e n t e din Table 2.

P revious work on temperature ramp rate wouldpredict approximately the 68 psig peak pressure pulserecorded for a 2.25 inch diameter disk.

The relationship of peak pre s s u re pulse (spike) vs.vent area to working-heated volume ratio is presentedin Figure 3.

For the disk size of interest which relates to theSpec. 57 container, 1.75" diameter, the peak pre s s u repulse (spike) was 232.5 psig. It happens that the venta rea to working volume, as well as the working vol-ume to vent area, for this size disk is 1.00. From thetime the disk relieved to the time of peak pre s s u rewas approximately half a minute. In all cases the peaktemperature was approximately 350° C.

T h e re f o re, for scale-up to the D.O.T. Spec. 57 con-tainer used by GEO Specialty Chemicals, which has421 working gallons of volume and contains 3,500

88 June 2002 Process Safety Progress (Vol.21, No.2)

Table 1. Results of four temperature ramp tests.

Table 2. Results for peak pressure pulse vs. venting area with constant ramp rate.

Process Safety Progress (Vol.21, No.2) June 2002 89

pounds of dicumyl peroxide, with a 22.5 inch diame-ter frangible disk (1.00 A/V ratio), a peak pre s s u re of232.5 psig was predicted from the 10 liter studies, ifthe calculated heating rate assumption is accurate andverified in full-scale testing and is 6° C/min/min.

C O N TAINER STRUCTURAL EVA L U AT I O N

Design CriteriaP rocess vessels, for example, pressurized work tanks,

reactors, etc., are designed based on material of con-struction yield stresses, or the point at which first elon-gation or deflection occurs. Then, to avoid appro a c h i n gyield or elongation, which could lead to fatigue, a con-servative working pre s s u re of 25% of that pre s s u re ischosen as an upper limit. For a vessel that ro u t i n e l ycycles in normal operation over several decades ofexpected life, this conservative approach is understand-able. H o w e v e r, when applied to a shipping container,which may experience deflection or elongation oncein its working lifetime due to an internal decomposi-t i o n / o v e r p ressurization as the result of an emerg e n c ysituation, for example, an external fuel fire, thisa p p roach is viewed as excessively conservative andrestrictive.

A more realistic approach for a shipping containersuch as the D.O.T. Spec. 57 portable tank and UnitedNations 31-AY Intermediate Bulk Container (IBC) is topermit deflection on a one-time basis during an emer-gency, with the proviso that the container be re t i re df rom service. Then the design bases can work off ofmaterial of construction true strength, the ultimates t ress, or the point at which failure would occur. Thisapproach was tested and proven to be valid.

A D.O.T. Spec. 57 portable tank from the GEO Spe-cialty Chemicals’ fleet, which had seen 20 years ofactive service and was similar in all design respects tothe container planned for use in an EMRTC/NMT fullscale U.N. 6(c) burn, was selected. The design basisfor this atmospheric vessel based on yield stress was 4barg, which, with a 25% factor, permitted it to be usedat atmospheric pressure (1 barg).

Hydrostatic TestingThe container was hydrostatically tested. While

there was deflection of the flat heads, top and bottom,with increasing applied pre s s u re, there was no struc-tural failure, as defined by breach or fragmentation at288 psig (19.6 barr), where the test was discontinued.Fragmentation, not deflection, is the true point of con-cern in any incident.

Curvilinear Finite Element TestingThe container was further evaluated from a struc-

tural-mathematical approach. Curvilinear finite ele-ment analysis (FEA), which is frequently used todefine ASME pre s s u re vessels, was employed. Themethod, by which finite elements of the container areevaluated separately, confirmed the hydrostatic testresults by predicting deflection at the heads, but nostructural failure as defined by breach or fragmenta-tion to pressures greater than 20 barg.

T h e re f o re, with a safety factor of permitting only 85%of the demonstrated hydrostatic pre s s u re limit, the Spec.57 could reasonably be expected to contain the pre d i c t-ed ~ 230 psig maximum pre s s u re pulse from the 10 literp rediction for a full-scale burn with the standard pero x-ide; dicumyl peroxide and an A/V = 1.00.

FULL-SCALE UNITED NATIONS 6(C) BURN

Test SiteP rojections from the 10 liter studies were extended

to a full-scale United Nations 6(c): Fuel Fire Test. TheE n e rgetic Materials Research and Testing Center at theNew Mexico Institute of Mining & Te c h n o l o g y( E M RTC/NMT) in Socorro, New Mexico, test rangefacilities were once again utilized. Tests were wit-nessed by D.O.T. officials, as well as OPPSD/SPImembers, while a video system permitted it to bere c o rded. Pre s s u re and temperature telemetry wassent to a remote location for acquisition and analysis.Test results, along with experimental set-up and pro c e-d u res, are presented in EMRTC/NMT Report FR-99-03.

Figure 2. 10 liter results: Peak pressure pulse vs.temperature ramp rate.

Figure 3. 10 liter results: Peak pressure pulse vs. ventarea to working-heated volume ratio.

Experimental Test Material. GEO Specialty Chemicals’ Di-Cup® R,

dicumyl peroxide, an organic peroxide, Type F, 5.2,UN 3110, PG II, was utilized as the test material. It is acolorless to pale yellow solid at ambient conditions.The purity was 99.7% as dicumyl peroxide with amelting point (M.P = 101° F). The mater ia l wil ldecompose before the boi ling point is re a c h e d .Decomposition products are flammable and includemethane. A total of 3,500 pounds of the material wasinvolved in the test.

Test Container. A D.O.T. Spec. 57 container, designedand custom fabricated for GEO Specialty Chemicals,was used for the test. It was identified as Serial No. 11-88-7081-F6. It had a tare weight of 765 pounds, a con-tainer volume of 460 gallons, and a height of 66 inches.A protective 3/16 stainless steel rim of 4.5 inches fittedabout the top of the container added to the totalheight. A 20 psi frangible disk (relief vent) measuring22.5 inches in diameter was positioned and centered onthe top head. It was secured with a clamping ringt o rqued to 20 ft lbs at the locking bolt. An integral partof the disk design incorporated an additional 3 inchrelief device, designed to melt at 300° F to provide earlyrelief before the primary disk was engaged. The totalweight, including organic peroxide, was 4,265 pounds(see Figure 4).

The container had two minor modifications to per-mit test telemetry to be transmitted:1. Fifteen 1/4 inch diameter holes were drilled into

the top of the container to permit access of thet h e rmocouples. These were made pre s s u re tightby the use of Swagelok fittings.

2. An existing dip pipe used to pump out the con-tents of the container was modified for use as thep re s s u re measurement connection. The 1.25 inchdiameter pipe reaches to the bottom of the con-tainer. At a point just under the top of the contain-er, at a position clearly in the vapor space, a 2 inchdiameter hole was cut into the pipe to facilitatethe external connection of the pre s s u re measuringdevices, without making a significant change inthe container’s design.

Test Apparatus Test Assembly. The package consisted of the test con-

t a i n e r, a test stand, pipes to support the pre s s u re andt e m p e r a t u re telemetry lines and a 12 foot diameter con-tainment tank to contain the JP-4 fuel. A 6 inch layer ofwater was added to the bottom of the containment tank,then, the fuel was added to just below the top of thetank’s lip. As it burned off, additional fuel was pumpedinto the bottom of the tank through the water layer top rovide the needed media to sustain the fire.

90 June 2002 Process Safety Progress (Vol.21, No.2)

Figure 4. Experimental tests of full-scale United Nations 6(c) burn.

Process Safety Progress (Vol.21, No.2) June 2002 91

T h e rm o c o u p l e s . Fifteen K-Type thermocouples, 1/8inch, with grounded junctions and 1/8 inch 304 stain-less steel sheaths were installed by GEO SpecialtyChemicals prior to shipping (Omega Engineering, Inc.CASS-188-84-NHX, CASS-188-60-NHX, and CASS-188-48-NHX). The internal thermocouples were arrangedin a vertical plane through the center of the containerand at three heights: near the top, at the center, andnear the bottom. Radially, they were placed at thecenterline, at a point half-way from the wall to thecenterline, and at a point 3 inches from the wall. Toreduce the chance of failure, eight exited on the eastside and seven on the west side. Five additional K-Type, stainless steel sheathed, ungrounded therm o-couples (Omega Engineering, Inc. CASS-116-U-12)w e re used to measure the temperatures on the exteri-or of the package. One was located on the west skin,one on the east skin, one in the west side flame, onein the east side flame, and one under the containernear the west side. The west skin thermocouple w a sat the mid-point near internal thermocouple #3. Theeast skin thermocouple was at the mid-point near inter-nal thermocouple #12. Figure 4 identifies locations.

P re s s u re Devices. Two Sentra 280E variablecapacitance pre s s u re transducers (one 500 psi andone 250 psi) remotely monitored the pre s s u re at thetop of the container. Oil (Thermosol 60) was fedt h rough 1/4 inch stainless steel lines to each trans-ducer to provide a non-compressible pre s s u re medi-um to the devices.

Te m p e r a t u re Pro t e c t i o n . All of the therm o c o u p l ew i res from the top of the container were enclosed in 4inch steel pipes with a wall thickness of 1 inch to pro-vide support and protection. The transducer lines wereencased in a 3.5 inch diameter pipe with 3/4 inch walls.Air was blown through the outer pipe at appro x i m a t e l y100 cu ft/sec on the outside of the oil-filled lines. Theends of the pipe that were exposed to direct flame wereencased in calcium silicate insulation.

Test ProceduresAfter the container was placed on the test stand,

the thermocouples (internal and external) wereattached to the computer links. Next, the transducerlines were filled with oil and connected to the trans-ducers and pipe tee, respectively. Six inches of waterwas added to the bottom of the fuel tank for safetypurposes and both electric diaphragm pumps werecycled to ensure that they were functioning corre c t l y .The following day, fuel was pumped to fill the fueltank. Two “puff bags,” or delayed fuse bags, wereused to ignite the fuel. The fuel level in the tank wasm o n i t o red by video, and was added when necessaryto maintain a high level of heat and flame on the testc o n t a i n e r. Wind direction and velocity was monitore dt h roughout the test. Based on a rough use of appro x i-mately 2,000 gallons of fuel for the two-hour test, itwas determined that the burn rate was appro x i m a t e l y17 gallons/min.

P re s s u re Data Collection. The signal from eachpressure transducer was transmitted to separate Straw-berry Tree, Inc., Dynares 16-channel Analog/DigitalI/O boards that were installed in Pentium computers.

These systems were programmed to collect data at100 MHz.

Te m p e r a t u re Data Collection. The signals fro mseven of the thermocouples were transmitted to aStrawberry Tree, Inc., Dynares 16-channelAnalog/Digital I/O board that was installed in a Pen-tium computer (Computer #1). Also, data from thewest skin, west air, and underside of container, andtwo additional thermocouples were re c o rded on thiscomputer system. The additional thermocouples re a dfuel temperature at 6 and 12 inch depths in the fueltank. The remaining eight internal therm o c o u p l e stransmitted data to a second Strawberry Tree, Inc.,D y n a res 16-channel Analog/Digital I/O board thatwas installed in a Pentium computer (Computer #2).In addition to these signals, signals from the east skinand east air were also re c o rded. Both systems wereset to record data at 100 MHz.

U.N. 6 (C) FULL-SCALE BURN TEST RESULT S

Burn Sequence of EventsAt five minutes before ignition of the JP-4 fuel (T- 5

min), monitoring and data acquisition systems wereturned on. Wind velocity was measured at 4 to 5 mph,which was within the allowable 11 mph set by U.N.6(c) format. At time Zero (t = 0), the igniters weretripped and a fire was observed on the surface of thefuel tank.

E x t e rnal skin temperatures rapidly rose to 450° F,while internal temperatures reached 112° to 125° F at(t+ 10 min) at the probes closest to the walls and bot-tom. Within minutes, the 3 inch relief device melted,indicating temperatures at the top of the container at> 300° F. When it gave way, a low-velocity jet of lightdecomposition gases (single phase) could be seenemanating from it. The gases, which were most likelymethane, ignited. This would indicate decompositionat the walls and bottom of the container with earlyrelease of internal pre s s u re as designed. The primaryfrangible disk was still intact.

At (t+ 23 min), external skin temperatures hadreached 500° to 800° F, while temperatures thro u g h-out the interior of the container were at least 170° F,with higher temperatures at the walls and, particular-ly, the bottom of the container. A high velocity jet ofgas could be seen emanating from the 3 inch vent, butt h e re was no measurable internal pre s s u re and theprimary frangible disk was still intact.

Release of the primary relief device and maximump re s s u re pulse (spike) came at (t+23.54min). Themaximum pre s s u re re c o rded was 15 and 25 psig onthe two respective monitoring systems. The pre s s u respike was brief in duration, (< 0.15 seconds), andre q u i red the 1,000 points/second re c o rding rate todetect and measure accurately. There was a majortwo-phase release of material from the vent indicatingsignificant amounts of non-decomposed pero x i d eleaving the container prior to its decomposition, ener-gy release, resultant heat release, and re s u l t a n tgaseous pre s s u re generation. There was a minor sec-ondary pre s s u re pulse at (t+ 23.65 min) or (0.11) sec-

onds after the primary pulse, and measured 1 to 2psig with a duration of ~0.03 seconds. During thistime there was a rapid surge of internal temperatures.

At ( t+ 35 to 45 min), the internal temperatureranged from 345° to 800° F. There was rapid fluctua-tion on individual probes indicating internal turbu-lence and/or mixing/roiling effects, with the pro b e sbeing alternately exposed to vapor and liquid whichvaried considerably in temperature. Two-phase emis-sions from the relief device were still occurring butwith rapidly diminishing volume.

By (t+ 50 min) fires due to internal peroxides haddied down and temperatures started to diminish. Thefuel fire was allowed to continue for another 70 min-utes or a total burn time of 120 minutes. No furthers u rges of temperature and/or pre s s u re was observedin that time period. After the fuel fire was extin-guished and the apparatus had cooled down, a visualinspection was made of the container. It was essential-ly empty with only some evidence of char on theinternal walls and heating coils.

Table 3 and Figures 5a and b represent typical tem-perature and pressure profiles for the burn.

Post-Burn Container ExaminationPost-examination of the container indicated there

had been a slight deflection of the top and bottom flatheads. There was no evidence of loss of structuralintegrity, breach, or fragmentation. The container hadrelieved the peroxide decomposition and overpressur-ization successfully as designed.

American Petroleum Institute’s API 520/521CalculatedHeat-up Rate vs. Full Scale Results

The United Nations approved calculation for heat-up rate in a fuel fire for a non-insulated tank (API520/521) predicted 6.0° C/min/min. Test work in the 10liter bench-scale vessel was conducted at 6.0° C/min.Post full-scale burn calculations of actual heat-up ratein the Spec. 57 container indicated 6.0+/-0.3° C/min.The API 520/521 prediction was confirmed and the 10liter studies had been conducted there f o re at the cor-rect heat-up rate to predict the heat-up rate peak pres-sure pulse for the full-scale burn.

10 Liter Pressure Pulse Prediction vs. Full Scale ResultsTest runs conducted on the 10 liter vessel with equiv-

alent A/V venting ratio of 1.00 sq.in./working-heated

92 June 2002 Process Safety Progress (Vol.21, No.2)

Table 3. Results of full-scale U.N. 6 (c) burn.

Figures 5a and b. Full-scale Spec. 57 burn.

Thermocouples 1, 3,and 6 in the right

(west) side of tank.

Process Safety Progress (Vol.21, No.2) June 2002 93

gallon with a heat-up rate of 6.0° C/min predicted amaximum pre s s u re pulse of ~230 psig. During the full-scale burn test, the maximum pre s s u re pulse was 15 to25 psig, an order of magnitude lower than expected.

The larger venting orifice size, 22.5 inch diameter vs.1.75 inch diameter, permitted a more efficient nozzle-e ffect, and two-phase transport with minimized wall-effect, as a result.

This was not unexpected. Other works indicatedi m p roved efficiency and reduced pre s s u re withi n c reasing scale. Scale diff e rence is re g a rded as thereason for lower peak pre s s u res as was demonstratedby earlier proprietary work conducted by Herc u l e sIncorporated wherein an electrically heated 65 gallonD . O . T. Spec. 57 container was tested with a peakpressure of 170 psig for a similar design ratio of A/V =1.00 (see Figure 6).

The 10 liter studies there f o re re p resent an extre m e l yconservative method for safely predicting peak pre s s u repulse for a larg e r, full-scale, commercial container.

C O N C L U S I O N S• The 10 liter OPPSD/SPI designed test vessel is suit-

able for organic peroxide decomposition studies.R e p roducibility has been demonstrated and iscomparable in results to the U.N. Appendix 5, Te s tMethod, test vessel.

• There is a near-linear relationship between heat-uprate and maximum pre s s u re pulse for a constantA/V; venting area to working-heated volume ratio.

• H y d rostatic testing is an acceptable method ford e t e rmining the ultimate structural strength of acontainer through destructive testing.

• Linear and curvilinear finite element analysis (FEA) isan alternative method to hydrostatic testing andacceptable as a non-destructive method for identify-ing the ultimate, structural strength of a container.

• The U.N. approved API 520/521 method for calcu-lating the heat-up rate in a fuel fire was verified asaccurate in full-scale testing.

• The 10 liter test is a very conservative predictor ofthe full-scale maximum pre s s u re pulse during ano rganic peroxide decomposition/overpre s s u r i z a t i o n .

• The nozzle efficiency for venting a two-phase mix-t u re increases with increasing scale and, there b y ,reduces the maximum pressure pulse significantly.

• Reduced maximum pre s s u re pulses observed dur-ing the full-scale burn are attributable to impro v e dnozzle efficiency and two-phase transport withincreasing scale.

• The OPPSD/SPI Emergency Venting Methodologyfor establishing the safety of a specific peroxide foran approved container has been demonstrated.Likewise, the methodology can be applied todesign a new container for an existing or neworganic peroxide.

• The OPPSD/SPI Methodology is a suitable altern a-tive method to U.N. Appendix 5 Sample Method. Ita ff o rds the advantage of more recent technicaladvances in the determination of container ulti-mate strength.The OPPSD/SPI Methodology follows, and is pre-

sented in its entirety as submitted to the D.O.T. forconsideration in September 2000. Identificationassignment: P-1404.

EXAMPLE OF A TEST METHOD FOR VENT SIZING: OPPSD/SPI METHODOLOGY

IntroductionThis example of a method for vent sizing is used to

determine the required emergency vent capacity to befitted to a specific IBC or portable tank for a particularo rganic peroxide, Type F, or self-reactive substanceType F, or any formulation thereof. The method isbased on experimental data which indicates that, foro rganic peroxides or self-reactive substance form u l a-tions, the ratio of the minimum emergency vent are ato the capacity of the IBC or tank is constant and canbe determined using a reduced-scale tank with a 10liter capacity. In the tests, the reduced scale tank isheated at rates equivalent to that given by completef i re engulfment or, in the case of insulated IBCs orportable tanks, the heat transfer through the insulationwith the assumption that 1% of the insulation is miss-ing (see 4.2.1.13.8 and 4.2.1.13.9 of “Recommenda-tions on the Transport of Dangerous Goods, ModelRegulations,” United Nations, Eleventh Revised Edi-tion). Other methods may be used provided that theyadequately size the emergency relief device(s) on anIBC or portable tank to vent all the material evolvedduring self-accelerating decomposition or a period ofnot less than one hour of complete fire engulfment.

Wa rning: The method does not take into accountthe possibility of initiation of deflagration. If this is apossibility, particularly if initiation in the vapor phasecan propagate to the liquid phase, then tests should beperformed which take this into account.

Apparatus and materialsThe reduced-scale tank consists of a stainless steel

test vessel with a gross volume of 10 liters. The top ofthe vessel, optionally, is provided with either a 1 mmopening, which simulates the pre s s u re relief valve (PRV )of the IBC, or portable tank, or a real PRV of a diameterthat is scaled using the vent area to vessel volume ratio.

Figure 6. Results of an earlier test.

A second opening simulates the emergency vent open-ing and is closed by a bursting disk. The diameter ofthis vent opening can be varied by using orifice plateswith diff e rent apertures. The bursting pre s s u re of thedisk fixed to the 10 liter vessel should be equal to themaximum rupture pre s s u re of the bursting disks to befitted to the IBC or portable tank. This pre s s u re shouldbe lower than the test pre s s u re of the IBC or portabletank involved. Usually, the bursting pre s s u re is set at alevel that can cope with the pre s s u res encountered dur-ing normal transport conditions, such as hydro s t a t i cp re s s u re from the liquid due to turnover of the IBC orportable tank, slopping of the contents, etc. The 10 litervessel should be provided with a bursting disk with aset pre s s u re in the range of the disk(s) fitted on the tankor IBC as to be used in transport. For safety, it is re c o m-mended to provide the test vessel with an extra burstingdisk (bursting pre s s u re approximately 80% of the designp re s s u re of the 10 liter test vessel) with a large openingfor additional emergency venting of the test vessel inthe event that the chosen orifice diameter is too small.

The outer surface of the test vessel, below the liq-uid level, is provided with an electrical heating coil orcartridge heaters connected to a power supply. The 10liter test vessel contents should be heated at a con-stant rate independent of the heat being generated bythe organic peroxide. The resistance of the heatingcoil or cartridge heaters should be such that, with thepower available, the calculated heating rate (see sec-tion 3) can be achieved. The whole vessel is insulatedwith rock wool, cellular glass, or ceramic fiber.

The temperature inside the vessel is measured bymeans of three thermocouples, two located in the liq-uid phase (near the top and bottom) and one in thegas phase. Two thermocouples are used in the liquidphase in order to check the homogeneity of the heat-ing. The pre s s u re is re c o rded by a pre s s u re transduc-er(s) capable of recording slow and fast (at least 1,000point/sec.) changes in pre s s u re. Examples of test ves-sels are illustrated in Figure 1. Additional inform a t i o nmay be obtained if the vessel is mounted in a traydesigned to collect any solids or liquids ejectedand/or on a scale to measure weight loss vs. time.

The tests should be perf o rmed at a test site with suit-able safety distances. Alternatively, the test can be per-f o rmed in a bunker provided with sufficient ventilationand vent openings to prevent pre s s u re build-up. Explo-s i o n - p roof electrical equipment should be used in sucha bunker to minimize the risk of ignition. H o w e v e r, thetests should be perf o rmed on the assumption that thedecomposition products will ignite.

Calculation of the heating rate to be used in the testIf an IBC or portable tank is non-insulated, the heat

load to the shell as given in 4.2.1.13.8 of the ModelRegulations is re q u i red. For an insulated IBC or tank,the U.N. Model Regulations re q u i re that the heat loadto the shell be equivalent to the heat transfer thro u g hthe insulation, plus the heat load to the shell, on theassumption that 1% of the insulation is missing.

The following information on the IBC or portabletank, and organic peroxide or self-reactive substance,is needed for the heating rate calculation:

Fr = fraction of tank directly heated (1 if non-insulated, 0.01 if insulated) [ - ]M = total mass of organic peroxide and diluent [kg]K = heat conductivity of the insulation layer

[ W. m- 1. K- 1]L = thickness of insulation layer [m]U = K/L= heat transfer coefficient [W.m-2.K-1]A = wetted area of IBC or portable tank [m2]Cp = specific heat of the organic peroxide or self-reactive substance formulation [J.kg-1.K-1]Tpo = temperature of organic peroxide or self-reactivesubstance formulation at relieving conditions [K]

Heat input, qi (W), via i n d i re c t l y exposed surf a c e(insulated part), is calculated by Equations 1 and 2:

qi = 70961 * F * (1 - Fr) * A0.82 (1)

whereF = insulation factor;

F = 1 for non-insulated shells, or

In the calculation of F, a multiplication factor of 2 isi n t roduced to take into account a 50% loss in insula-tion efficiency in an incident.

Heat input, qd (W), via the directly exposed surface(non-insulated part), is calculated by Equation 3:

qd = 70961 * F * Fr * A0.82 (3)

whereF = insulation factor = 1 (non-insulated)

The overall heating rate, dT/dt (K/min), due to fireengulfment, is calculated by Equation 4:

Example 1. Insulated portable tankFor a typical 20 m3 insulated portable tank:

Fr = fraction of tank directly heated = 0.01Mt = total mass of organic peroxide and diluent =

16268 kgK = heat conductivity of the insulation layer =

0.031 W.m-1.K-1

L = thickness of the insulation layer = 0.075 mU = heat transfer coefficient = 0.4 W. m- 2. K- 1

A = wetted area of portable tank = 40 m2

Cp = specific heat of the organic peroxide form = 2000 J .kg-1. K-1

Tm = temperature of peroxide at relieving conditions = 100° C

and

94 June 2002 Process Safety Progress (Vol.21, No.2)

F = 2 ∗U∗ (923 − Tpo)

47032for insulated shells.

(2)

dT / dt =(q i + qd )

Mt ∗ Cp

∗ 60(4)

Process Safety Progress (Vol.21, No.2) June 2002 95

qd = 70961 * 1 * 0.01 * 400.82 = 14611 W

Example 2. Non-insulated IBC

For a typical 1.2 m3 non-insulated stainless steelIBC (only direct heat input, qd):

Fr = fraction of tank directly heated = 1Mt = total mass of organic peroxide and diluent =

1,012 kgA = wetted area of IBC = 5.04 m2

Cp = specific heat of the organic peroxide form = 2190 J .kg-1. K-1

and

qd = 70961 * 1 * 1 * 5.040.82 = 266 kW

ProcedureFill the test vessel shell with the amount of org a n i c

p e roxide or self-reactive substance re q u i red to givethe same degree of fill (by volume of the shell) as tobe used in the portable tank (maximum degree of fill90%, by volume) and then install the re q u i red orificeplate* and bursting disk. For example, it is commonpractice to fit four 250 mm diameter bursting disks toa 20 ton portable tank. This corresponds to a test ves-sel orifice diameter of about 11 mm.

* It is recommended that either small-scale ventexperiments (100 to 200 ml scale) or experimentsusing a very strong vessel (> 100 bar) be perf o rm e dprior to the perf o rmance of the 10 liter vent test ino rder to obtain information on pre s s u re effects fro mthe test substance and on the required orifice diameterto be used in the first 10 liter scale vent test. For safety,start with the largest orifice.

The vessel is heated at the desired rate by applyingpower to the heating coil or cartridge heater. A higherthan calculated heating rate may be applied initiallyuntil a temperature 5° C above the self-acceleratingdecomposition temperature (for a 50 kg package) ofthe organic peroxide or self-reactive substance isreached. The calculated heating rate should beapplied once this temperature is reached. The temper-a t u re and pre s s u re in the test vessel are re c o rded dur-ing the entire experiment. After rupture of the burst-ing disk, the temperature should be maintained fora p p roximately 30 minutes more to be sure that all

d a n g e rous effects are measured. After the test, the ves-sel should not be approached until the contents havecooled.

The diameter of the orifice should be varied (ifnecessary) until a suitable opening is determined atwhich the maximum recorded pressure is:• for portable tanks tested according to 4.2.1.13.4,

not more than 85% of the maximum pre s s u reb e f o re failure as determined for the portable tankbased on the hydrostatic limit or as determined byFinite Element Analysis, but not to exceed 25 barg.

• for IBCs tested according to 6.5.4.8.4 of the ModelRegulations, not more than 85% of the maximump re s s u re before failure as determined for the IBCbased on the hydrostatic limit, or as determined byFinite Element Analysis, but not to exceed 25 barg. The minimum test pre s s u re of the IBC should be at

least as specified in 6.5.4.8.4 of the Model Regulations(e.g., 2.0 bar for metal IBCs) or higher as tested byh y d rostatic pre s s u re testing or by Finite ElementAnalysis (FEA). The minimal test pre s s u re of theportable tank should be 4.0 barg (see 4.2.1.13.4 of theModel Regulations). Since these portable tanks andIBCs are used to transport organic peroxides (andother self-reactive substances) and are not pro c e s svessels, permanent deformation is permitted duringh y d rostatic peak pre s s u re testing so long as there isno fragmentation. A shipping vessel, should there bean incident resulting in permanent deformation, willbe discarded without exception (no further use).

The step size used should be related to the optionsavailable in practice for the IBC or portable tank, thatis larger vent sizes or more vents. The test should bep e rf o rmed in duplicate, with the minimum total venta rea having sufficient capacity. An altern a t i v ea p p roach is to perf o rm a series of six runs at varyingorifice sizes so as to generate a continuous plot ofpeak pre s s u re vs. the venting area to working volumeratio. This permits improved working latitudes withrespect to the approval of additional peroxides and/orthe design of additional containers.

Test criteria and method of assessing the resultsThe minimum or suitable (if it is acceptable to use

a vent size larger than the minimum vent size) IBC orportable tank vent area, AIBC or Aportable tank ( m2), canbe calculated using the minimum orifice vent are a ,Atest vessel (m2), determined in the 10 liter test at whichthe maximum pre s s u re is not more than specified inthe previous section of this method, and the volumesof the test vessel (Vtest vessel, m

3) and IBC or portabletank (VIBC or Vportable tank, m

3). The minimum total IBCor portable tank vent area is given by:

For IBCs: AIBC = VIBC * (Atest vessel/Vtest vessel)

For portable tanks: Aportable tank = Vportable tank * (Atest vessel/Vtest vessel)

q i = 70961∗ 2 ∗ 0.4 ∗ (923 − 373)

47032∗

1 − 0.01( ) ∗ 400.82 =13533W

dT / dt =13533 +14611( )16268 ∗2000

∗ 60 = 0.052K.min-1

dT / dt =0 + 266000( )1012∗ 2190

∗60 = 7.2K.min-1

ExampleFor a typical organic peroxide in a 20 m3 i n s u l a t e d

portable tank:

Atest vessel = Minimum suitable orifice area found intest = 9.5 •10-5 m2

Vportable tank = Volume of portable tank = 20 m3

Vtest vessel = Volume of test vessel = 0.01 m3

Aportable tank = 20 * (9.5 • 10-5/0.01) = 0.19 m2

Utilizing the peak pre s s u re curve for a given stan-d a rd peroxide generated in a 10 liter study in the pre-vious section on “pro c e d u re,” another pero x i d eexhibiting a lower peak pre s s u re for the same ventingratio may use the same full-scale container withoutfurther testing of the container or the peroxide in thatcontainer (full-scale). Likewise, another pero x i d ewhich exhibits a higher pre s s u re for a given ventingratio in the 10 liter 6 point study may be used in thefull-scale container so long as the container’s ventingratio is increased so as to produce a lower peak pre s-s u re than the standard organic peroxide pre v i o u s l ytested.

Note: It is recognized in developing this method forvent sizing that dicumyl peroxide behaves diff e re n t l ythan most other organic peroxides in vent testing.T h e re f o re dicumyl peroxide can continue to beshipped in the portable tanks and IBCs curre n t l ya p p roved by the D.O.T., based on extensive testingand proven performance.

L I T E R ATURE CITED1. Banks, M., et al., “Safe Emergency Venting of

O rganic Peroxide Containers,” E M RTC Report FR-9 8 - 0 7, Research conducted for the Organic Pero x-ides Producers Safety Division of the Society of thePlastics Industry (OPPSD/SPI), Energetic MaterialsR e s e a rch & Testing Center, New Mexico Instituteof Mining & Technology, Socorro, NM 87801, Feb-ruary 1998.

2. Banks, M., et al., “Effects of Heating Rate onO rganic Peroxide Reactions,” E M RTC Report FR-9 9 - 0 3, Research conducted for the OPPSD/SPI,E n e rgetic Materials Research & Testing Center,New Mexico Institute of Mining & Te c h n o l o g y ,Socorro, NM 87801, March 1999.

3. Code of Federal Regulations, Title 49 CFR, Sub-title “B” (Other Regulations Relating to Tr a n s p o r t a-tion), Chapter 1 (Research and Special Pro g r a m sAdministration, D.O.T.), Subchapter “C” Haz-a rdous Materials Regulation Part 178 (Specifica-tions for Packagings), Subpart “N” Interm e d i a t eBulk Container Perf o rmance—Oriented Standard sand Subpart “O” Testing of Intermediate Bulk Con-tainers.

4. C O S M O S / M, Finite Element Analysis System,Structural Research and Analysis Corporation,12121 Wi l s h i re Blvd., Los Angeles, CA 90025,October 1996.

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