- Email: [email protected]
Prevention of gasoline vapor explosions in portable fuel containers
Journal of Loss Prevention in the Process Industries 61 (2019) 249–254
Contents lists available at ScienceDirect
Journal of Loss Prevention in the Process Industries journal homepage: www.elsevier.com/locate/jlp
Prevention of gasoline vapor explosions in portable fuel containers a,∗
A. Rangwala , R. Zalosh a b
T
a,b
Worcester Polytechnic Institute, Worcester, USA Firexplo LLC, Wellesley, USA
A R T I C LE I N FO
A B S T R A C T
Keywords: Fuel container Flame arrester Explosion prevention Butane-air mixture
Portable Fuel Containers (PFCs) made for consumer use can, under unusual circumstances, develop a flammable atmosphere in the container headspace. In order to prevent an inadvertent ignition from causing flame propagation into this headspace and a subsequent explosion or flame jetting, PFC manufacturers are developing prototype Flame Mitigation Devices (FMDs) for installation in the PFC. A test method is described in this paper to determine if the installed FMD will indeed prevent flame entry into the PFC in a high-challenge flame propagation scenario. The method entails the use of a butane-air mixture ignited in a 5 cm diameter, 12 cm long tube attached to either the container neck or a spout on the container neck. Two concept FMD designs have successfully prevented repeated attempts at flame propagation into the PFC and have also produced encouraging results in tests for fuel flow restriction, duel dispensing nozzle friction, and prolonged fuel exposure. Versions of these tests are currently being promulgated in a draft ASTM standard on PFC FMDs.
1. Introduction
tilting testing and modelling reported by Elias et al. (2011,2013) showed the combinations of tilt angles and container fuel levels that can produce flammable vapor concentrations in both the neck and tip of the spout so that there is a continuous flame propagation path into the container from an external ignition source. Both Hasselbring (2006) and Stevick et al. (2011) conducted explosion testing with tilted fuel containers to demonstrate how this flame propagation can result in a container explosion and/or flame jetting from the open spout.
1.1. Portable fuel container vapor space flammability The headspace above the gasoline liquid level in a stationary portable fuel container is usually too fuel rich to support flame propagation within the container. However, there are several conditions in which a flammable atmosphere can form in at least a portion of the headspace. Flammability testing described by Elias et al. (2013) and by Gardiner et al. (2008), and by Vaivads et al (1994) showed how small fuel volumes and low temperatures, can produce flammable atmospheres in the container. Gardner et al. also showed how larger ethanol additions to gasoline formulations can also produce increased headspace flammability. Flame wick ignition tests reported by Hasselbring (2006) demonstrated that small fuel volumes (4.5 ml–9 ml in a 5-gallon container) can allow flame propagation into the open container and cause an explosion. Additional flammability testing by Stevick et al. (2011) showed how fuel weathering (also called aging) can increase the flammability envelope toward larger fuel volumes and higher ambient temperatures, particularly when the fuel container is left open. Observations of varying fuel evaporation rates and reduced vapor pressures due to aging were previously reported by Okamoto et al. (2009). Tilting of the fuel container in preparation for pouring also has a major effect on container headspace and spout flammability. Container
∗
1.2. Consumer fuel container incident scenarios There have been several documented consumer portable fuel container incidents that illustrate different fuel container incident scenarios. Stevick et al. (2011) report investigating incidents involving portable fuel containers that “have been left standing open with either their nozzles removed or kept un-capped for weeks or months before incidents.” They show evidence of one plastic fuel container that they say has experienced an explosion that caused the container to tear open. Hasselbring described an incident that occurred when a five-gallon container was being tilted to pour gasoline onto a small fire in order to increase the fire size. The result, according to Hasselbring, was a container explosion splattering the victim with burning fuel and causing burn injuries over 65% of his body. St. John (2017) described a tragic incident in which a young girl suffered fatal burn injuries when her father started pouring a mixture of
Corresponding author. E-mail address: [email protected] (A. Rangwala).
https://doi.org/10.1016/j.jlp.2019.06.006 Received 14 March 2019; Received in revised form 6 June 2019; Accepted 6 June 2019 Available online 08 June 2019 0950-4230/ © 2019 Published by Elsevier Ltd.
Journal of Loss Prevention in the Process Industries 61 (2019) 249–254
A. Rangwala and R. Zalosh
2. Flame mitigation experiments
gasoline and heavy petroleum distillate from a two-gallon portable container onto a fire in a fire pit. The container did not have a nozzle attached. St. John conducted forensic testing that produced flame jet lengths “in excess of 2 m” from the mouth of open fuel containers. These and other incidents show that portable fuel container flashbacks have occurred with both open containers and in containers with attached spouts. External ignition of the flammable vapours +in some cases causes the container to explode, and in other cases the container remains intact but becomes sufficiently pressurized to generate lengthy flame jets. None of the containers had installed flame arresters. This is in contrast to the U.S. Department of Transportation approved metal safety cans that are required to have both a flame arrester and a pressure relieving device (U.S. CFR §1926.152(a)(1)).
2.1. Butane-air mixture representation of fuel vapor mixture In choosing this method of testing, we considered using gasoline vapor directly however abandoned this idea for a few reasons. First, the composition of gasoline vapor is highly variable: depending on time of year, geographic location, blend, etc. This presents a challenge in developing an experimental method that is consistent and repeatable across multiple tests over a long period of time. Any small change in the characteristics of the gasoline can alter the flammability test results. Second, the use of gasoline vapor directly presents a second challenge in collecting the vapor for testing. If liquid is simply placed in the bottom of a PGC, the concentration of flammable vapor within the PGC is dependent on multiple factors (angle, temperature, time, etc.) (Elias et al. 2010; Elias, 2011). Again, this makes it difficult to perform consistent tests across multiple samples. A representative fuel/air mixture to model the flammability characteristics of gasoline vapor is therefore necessary. Gasoline container headspaces are composed of complex mixtures of hydrocarbons and ethanol, with the compositions varying with geographic region and season of the year, as well as the grade of gasoline. An example of some May 1999 gasoline samples in California reported by Harley et al. (2000) showed that approximately 50 wt percent of the regular grade gasoline headspace consisted of n-butane, n-pentane, and i-pentane. The higher-grade gasoline samples had slightly less of these components, with approximately equal amounts of n-butane and n-pentane. Since the other components, other than ethanol, had significantly higher molecular weights, the proportions of butane and pentane would be correspondingly higher on a volume percent or mol percent basis. The challenge a particular flammable vapor poses to a flame mitigation device depends on the vapor burning velocity and either quenching distance or Maximum Experimental Safe Gap (MESG). Published values of these flammability parameters are shown in Table 1 for n-butane, n-pentane, a nominal 100-octane gasoline formulation, and ethanol. The n-butane values are within 13% of the values for the other vapours, and is within 5% for MESG, which at least some organizations use as the parameter to determine applicability of flame arresters to gasoline and other flammable vapours. Since n-butane is both widely available and convenient to use for generating a readily repeatable representation of gasoline vapor headspace, it was selected as the fuel for Portable Fuel Container (PFC) flame mitigation device effectiveness testing. The use of a butane/air mixture also allows for the burning velocity to be varied by adjusting the concentration of butane in the mixture. If it is desired to test a different gasoline blend, this is easily accomplished in the laboratory by adjusting the concentration of butane in the mixture to match the burning velocity of the desired gasoline vapor. This allows for the testing of multiple fuel compositions using the same test apparatus. The effect of weathering on the fuel sample is also a consideration in this testing method. As gasoline ages, the composition of the headspace changes and the relative concentration of unsaturated hydrocarbons increases. These unsaturated hydrocarbons have higher burning
1.3. Industrial flammable liquid container scenarios and requirements Industrial flammable liquid container incidents tend to fall into two categories, both different than the consumer incidents described above. One category is the sustained fire exposure to stored closed containers. The safety can construction requirement to have a “spring-closing lid and spout cover designed to safely relieve internal pressure when exposed to fire” (NFPA 30-15) is well suited for this scenario. The second category of industrial incidents is when the container is used to dispense some special liquid for processing or a solvent for cleaning equipment and fixed surfaces. Ignitions in the second category lead to potential flashbacks that can challenge the container flame arrester. U.S. certification of these industrial safety cans include flashback requirements but not necessarily as stringent as the following flashback mitigation testing objectives for consumer fuel containers. 1.4. Flame mitigation testing objectives Both the portable consumer fuel container manufacturers and the cognizant U.S. government regulatory agency (the Consumer Product Safety Commission) acknowledge that dangerous consumer actions exposing flammable vapours to flames and other ignition sources cannot be totally eliminated and therefore support efforts to develop PFC flame mitigation devices. These organizations have been working through the ASTM voluntary standards organization to fund and oversee the development of a suitable test method to assess the effectiveness and reliability of installed flame mitigation devices. One major objective of portable fuel container Flame Mitigation Device (FMD) testing is to determine the effectiveness of the FMD in configurations that account for the incident scenarios described above and potential variations that might present even greater challenges. The flame arresting challenge depends on the flame speed approaching the FMD and the flammable mixture burning velocity and quenching distance within and on the other side of the FMD. Since these parameters depend on both the fuel vapor composition/concentration and the presence of potential flame acceleration conditions, the testing arrangement should entail a repeatable but representative fuel vapor concentration and a realistic high-challenge approaching flame speed conditions that include confinement associated with flame propagation through a container spout. Table 1 Comparison of vapor flammability properties. Property
n-Butane
n-Pentane
Gasoline (100 octane)
Ethanol
Laminar Burning Velocitya (cm/s) Quenching Diameterb (mm) Max Exp Safe Gap (MESG)c (mm)
45 3.4 1.066
46 2.4–3.4 1.016
40 No Data No Data
41 3.0 1.016
a b c
Burning velocity data from NFPA 68 Table D.1, except ethanol data from Konnov et al. (2011). Quenching diameter data from Grossel (2002) Table 5-3. MESG data from 33CFR Part 154 Appendix B (2002). 250
Journal of Loss Prevention in the Process Industries 61 (2019) 249–254
A. Rangwala and R. Zalosh
Fig. 1. FMD test setup for tests with spout (a) and without spout (b). Dimensions in mm.
spout mounted in the test stand. The FMD is not visible because it is installed in the neck of the PFC such that it can prevent flame propagation into the PFC with or without the attached spout. The aluminum foil deflagration vent installed on the cutoff bottom of the PFC is not visible in this side view of the mounted PFC. The polycarbonate ignition/flame propagation tube is visible in the upper right area of the photograph. The effectiveness of the FMD is easily discerned by seeing if the aluminum foil deflagration vent bursts after ignition (because of flame propagation through the butane-air mixture in the cutoff PFC). A video camera records the test results to confirm the presence of flame in the igniter/flame propagation tube and to provide a visual record of the test result.
velocities compared to saturated alkanes and may require further testing with a modified representative fuel mixture.
2.2. Experimental setup and procedure The FMD test configuration is shown in Fig. 1a for tests with the attached spout and in Fig. 1b for tests without the spout. Only a cut-off portion of the PFC with installed FMD is used in the tests so that a makeshift deflagration vent can be installed on the cut-off PFC. The butane-air mixture is made using mass flow controllers and tubing leading to a 50 mm diameter, 120 mm length, ignition and flame propagation tube attached to either the spout (a) or PFC (b). The air and butane mass flow controllers are programmed to produce a 2.83 vol percent butane in air mixture, corresponding to an equivalence ratio of 0.90. This mixture flows through the igniter tube and cutoff portable fuel container and into an exhaust tube leading to a gas analyzer as shown in Fig. 1. When the gas analyzer reading confirms that the desired butane concentration PFC has been reached in the igniter tube and the PFC, the exhaust line and gas supply line are disconnected in preparation for firing the approximately 10 J igniter in the transparent igniter/flame propagation tube. A close up of a butane-air mixture flame propagation in the igniter tube is shown in Fig. 2. The average flame speed or the speed of the flame after a run up across the length of the igniter tube equals 5 m/s. the flame speed was measured with a high-speed 5000 frames per second video camera. Fig. 3 is a photograph of a PFC with an installed FMD and attached
3. Concept flame mitigation devices A wide variety of concept FMDs have been tested using the apparatus and procedure described above. Figs. 4 and 5 show some examples of these FMDs illustrating how they are inserted in the PFC neck. The FMDs shown on the left and right in Fig. 4 are both flexible elongated plastic meshes with rigid plastic support frames. The FMD in the center of Fig. 4 is a rigid plastic mesh shaped into a cup/dome, while the FMD on the left of Fig. 4 is a cup shaped metal mesh. In the center of Fig. 5 is a single piece rigid plastic mesh, while Fig. 5 right shows a rigid plastic frame with a flexible composite carbon fiber mesh. 251
Journal of Loss Prevention in the Process Industries 61 (2019) 249–254
A. Rangwala and R. Zalosh
Fig. 2. Butane air flame propagation observed using a high-speed camera (5000 frames per second). The average flame speed is 5 m/s for a butane-air mixture at equivalence ratio of 0.9.
the basic flame quenching design. In the case of the unsuccessful metal mesh FMD, it appears that the basic mesh size is more open than the plastic mesh designs that were successful in this test. Since several of the concept FMDs are composed of combustible materials, there is concern about possible thermal degradation if these FMDs need to withstand multiple transient flame exposures. Therefore, five concept designs have been subjected to up to five flame propagation tests when installed in a PFC. Results are shown in Fig. 7. Two FMDs experienced significant mesh melting without any flame mitigation success. Another FMD experienced deformation that prevented successful mitigation after the first test. Two other FMDs, labelled Designs 3 and 4 in Fig. 7, successfully prevented five flame propagations into the PGC without experiencing any visible degradation. Design 3 is composed of a flexible sock-like fire-resistant fabric, while Design 5 consists of a rigid polymer with rows of approximately 1-mm square openings. Some of the successful FMD prototypes have also been tested by at least one PFC manufacturer for the prevention of flashbacks in container spills near small flames that produce flame jetting in the absence of an installed FMD in the container. The FMDs that were successful in the butane-air mixture tests described above were also successful in preventing flame jetting in tests similar to those described by St. John (2017). In fact, all six cylindrical mesh and screen disk FMDs used to prevent flame jetting in tests described by Stevick et al. (2011) were successful. However, the flame speed reported by Stevick et al. for the flame jetting tests was only 0.4 m/s, whereas the flame speed in the ignition tube tests described here is about 4 m/s, which is within 10% of the flame speed corresponding to the 0.45 cm/s butane burning velocity multiplied by a burned gas expansion ratio of 8. This indicates that the butane-air mixture flame propagation test described here is a more stringent challenge than the fuel spill simulation flame jetting tests.
Fig. 3. Portable Fuel Container mounted in Flame Mitigation Device test stand.
Many other versions of these types of concept FMDs have also been tested.
4. Flame mitigation device test results Fig. 6 shows two video frames of a test with a candidate FMD installed in a PFC that did not prevent flame entry into the interior butane-air mixture. The large vented flame is an obvious manifestation of the failed FMD effectiveness. Table 2 shows the results of the tests with the concept FMDs shown in Figs. 4 and 5. Four of these concept FMDs successfully prevented flame propagation into the PFC while the other two did not. In the case of the two similar design flexible elongated plastic meshes, the shorter version successfully prevented flame propagation, but the longer version was unsuccessful, probably because a small gap formed at the junction of the two half-sections. This illustrates the need for a successful FMD to have careful and robust fabrication details in addition to
5. Other requirements for portable fuel container FMD A commercially viable flame mitigation device for a portable fuel container must have certain fuel compatibility and durability characteristics besides being able to prevent flame propagation in a laboratory test. Three specific characteristics are:
• Allowing unrestricted fuel flow into and out of the container • Withstanding frictional contact with refuelling station dispensing nozzles
Fig. 4. Examples of early versions of FMDs in fuel container necks. 252
Journal of Loss Prevention in the Process Industries 61 (2019) 249–254
A. Rangwala and R. Zalosh
Fig. 5. Additional examples of concept FMDs.
• Withstanding
prolonged exposure to common fuel formulations without significant degradation
Table 2 Results of tests on examples of concept FMDs.
The authors and the WPI Combustion Laboratory staff have been working with the ASTM F15.10 Subcommittee to develop appropriate test methods for these FMD compatibility and durability characteristics. The flow restriction tests entailed measuring the flow times for 10 gpm (38 lpm) nominal flows into the PFC and inclined platform gravitational outflows. Four of the five FMDs were able to accommodate these flows with less than 15% reductions in the corresponding flows without any FMD in the PFC. The frictional durability test involved 25 repeated controlled insertions of a fuel dispensing nozzle into and out of the FMD equipped PFC. Two of the five concept FMDs experienced sufficient mesh degradation during these repeated insertions to prevent them from being able to successfully prevent flame propagation when tested with the method described in Section 2 of this paper. The FMD fuel exposure test conditions were daily exposures of the FMD to wetting by a standard ethanol containing gasoline formulation, and continuous 90-day exposure to the fuel vapor. Four of the five concept FMDs successfully survived the prolonged exposure to a 15% ethanol formulation (CE 15) without any apparent deterioration, but only two of the five successfully withstood a similar exposure to an 85% percent ethanol formulation (CE 85).
Figure with FMD
Description
Prevent Flame Entry into PGC?
Fig. Fig. Fig. Fig. Fig. Fig.
Flexible elongated plastic mesh Rigid plastic mesh dome Flexible elongated plastic mesh Cup shaped metal mesh Rigid plastic mesh cylinder Flexible composite carbon fiber mesh
Yes Yes No No Yes Yes
4 4 4 5 5 5
Left Center Right Left Center Right
Laboratories are members of the Subcommittee actively participating in the standard development, these organizations should be prepared to conduct the testing required to implement the standard. Furthermore, representatives of the Consumer Product Safety Commission are also active in this process so that the CPSC can simultaneously develop its position on any appropriate federal regulatory considerations in the sales and use of PFCs for the U.S. consumer market.
7. Conclusions A Portable Fuel Container Flame Mitigation Device test method has been developed to determine the effectiveness of installed FMDs in preventing the propagation of a butane-air mixture flame into the PFC. The butane-air mixture serves as a surrogate for the types of hydrocarbon-ethanol fuels commonly used in contemporary PFCs. The test method provides a high challenge to successful prevention of flame entry into the PFC, but at least two FMD designs have demonstrated capability to successfully prevent five repeated flame propagation tests. Prolonged fuel exposure, unrestricted fuel flow, and dispensing nozzle friction durability tests have also been developed for FMD equipped PFCs. An ASTM standard is currently under development delineating versions of the flame propagation, fuel exposure, and fuel flow and dispensing nozzle tests.
6. Test standard development approach and status ASTM Subcommittee F15.10 has been writing a draft “Standard Specification for Flame Mitigation Devices on Portable Fuel Containers.” The draft standard describes the flame propagation test described in Section 2 and the three types of fuel compatibility and mechanical durability tests described in Section 5. The draft standard requires a 5-gallon (20 L) capacity prototype containers with installed FMDs to pass specified versions of these tests. After the draft standard has been voted upon and adopted as an official ASTM standard, it will serve, along with ASTM F852, as the voluntary consensus standard applicable to Portable Fuel Containers sold in the U.S. Since representatives of Nationally Recognized Testing
Fig. 6. Video frame images before and after flame is vented from PFC. 253
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Fig. 7. Five FMDs after flame mitigation testing.
Acknowledgements
Gardiner, D.M., Bardon, M.F., Pucher, G., 2008. An Experimental and Modeling Study of the Flammability of Fuel Tank Headspace Vapors from High Ethanol Content Fuels. Nexum Research Corporation, Mallorytown, Canada. Grossel, S., 2002. Deflagration and Detonation Flame Arresters. AIChE Center for Chemical Process Safety. Harley, R.A., Coulter-Burke, S.C., Yeung, T.S., 2000. Relating liquid fuel and headspace vapor composition for California reformulated gasoline samples containing ethanol. Environ. Sci. Technol. 34 (19), 4088–4094. Hasselbring, L.C., 2006. Case study: flame arresters and exploding gasoline containers. J. Hazard. Mater. 130, 64–68. Konnov, A.A., Meuwissen, R.J., de Goey, L.P.H., 2011. The temperature dependence of the laminar burning velocity of ethanol flames. Proc. Combust. Inst. 33 (1), 1011–1019 2011. NFPA 30, 2015. Flammable and Combustible Liquids Code. National Fire Protection Association. NFPA 68, 2018. Standard on Explosion Protection by Deflagration Venting. National Fire Protection Association. Okamoto, K., Watanabe, N., Hagimoto, Y., Miwa, K., Ohtani, H., 2009. Changes in evaporation rate and vapor pressure of gasoline with progress of evaporation. Fire Saf. J. 44, 756–763. St. John, A., 2017. The science of flame jetting. NFPA J September-October 2017. Stevick, G., Zicherman, J., Rondinone, D., Sagle, A., 2011. Failure analysis and prevention of fires and explosions with plastic gasoline containers. J. Fail. Anal. Prev. 11455–11465. Vaivads, R., Bardon, M.F., Rao, V.K., Battista, V., 1994. Flammability of alcohol-gasoline blends in fuel tanks. Int. Assoc. Fire Saf. Sci. 4, 575–586.
The authors gratefully acknowledge the financial support and guidance from the ASTM F15.10 Subcommittee. They also want to acknowledge the excellent work of various WPI students and research staff in setting up and conducting the testing described here. References ASTM F852-99, 2006. Standard Specification for Portable Gasoline Containers for Consumer Use. ASTM. CFR Title 33, Part 154, 2002. Appendix B, Standard Specification for Tank Vent Flame Arresters, Code of Federal Regulations. Elias, B.E., Zalosh, R.G., Rangwala, A.S., 2013. Portable gasoline container headspace flammability. Fire Saf. J. 58, 248–257. Elias, B.E., Zalosh, R.G., Rangwala, A.S., 2010. Gasoline container vapor space flammability. In: 8th International Symposium on Hazards, Prevention, and Mitigation of Industrial Explosions, Yokohama, Japan Sep 5-10, 2010. Elias, B.E., Zalosh, R.G., Rangwala, A.S., 2011. Conditions affecting external flame propagation into a portable gasoline container: a summary of test methods and experimental findings. In: Eastern States Fall Technical Meeting, Storrs, University of Connecticut, Oct 9-12, 2011. Elias, B., 2011. Hazard Assessment of Portable Gasoline Container Flammability, MS Thesis. Worcester Polytechnic Institute.
254
Contents lists available at ScienceDirect
Journal of Loss Prevention in the Process Industries journal homepage: www.elsevier.com/locate/jlp
Prevention of gasoline vapor explosions in portable fuel containers a,∗
A. Rangwala , R. Zalosh a b
T
a,b
Worcester Polytechnic Institute, Worcester, USA Firexplo LLC, Wellesley, USA
A R T I C LE I N FO
A B S T R A C T
Keywords: Fuel container Flame arrester Explosion prevention Butane-air mixture
Portable Fuel Containers (PFCs) made for consumer use can, under unusual circumstances, develop a flammable atmosphere in the container headspace. In order to prevent an inadvertent ignition from causing flame propagation into this headspace and a subsequent explosion or flame jetting, PFC manufacturers are developing prototype Flame Mitigation Devices (FMDs) for installation in the PFC. A test method is described in this paper to determine if the installed FMD will indeed prevent flame entry into the PFC in a high-challenge flame propagation scenario. The method entails the use of a butane-air mixture ignited in a 5 cm diameter, 12 cm long tube attached to either the container neck or a spout on the container neck. Two concept FMD designs have successfully prevented repeated attempts at flame propagation into the PFC and have also produced encouraging results in tests for fuel flow restriction, duel dispensing nozzle friction, and prolonged fuel exposure. Versions of these tests are currently being promulgated in a draft ASTM standard on PFC FMDs.
1. Introduction
tilting testing and modelling reported by Elias et al. (2011,2013) showed the combinations of tilt angles and container fuel levels that can produce flammable vapor concentrations in both the neck and tip of the spout so that there is a continuous flame propagation path into the container from an external ignition source. Both Hasselbring (2006) and Stevick et al. (2011) conducted explosion testing with tilted fuel containers to demonstrate how this flame propagation can result in a container explosion and/or flame jetting from the open spout.
1.1. Portable fuel container vapor space flammability The headspace above the gasoline liquid level in a stationary portable fuel container is usually too fuel rich to support flame propagation within the container. However, there are several conditions in which a flammable atmosphere can form in at least a portion of the headspace. Flammability testing described by Elias et al. (2013) and by Gardiner et al. (2008), and by Vaivads et al (1994) showed how small fuel volumes and low temperatures, can produce flammable atmospheres in the container. Gardner et al. also showed how larger ethanol additions to gasoline formulations can also produce increased headspace flammability. Flame wick ignition tests reported by Hasselbring (2006) demonstrated that small fuel volumes (4.5 ml–9 ml in a 5-gallon container) can allow flame propagation into the open container and cause an explosion. Additional flammability testing by Stevick et al. (2011) showed how fuel weathering (also called aging) can increase the flammability envelope toward larger fuel volumes and higher ambient temperatures, particularly when the fuel container is left open. Observations of varying fuel evaporation rates and reduced vapor pressures due to aging were previously reported by Okamoto et al. (2009). Tilting of the fuel container in preparation for pouring also has a major effect on container headspace and spout flammability. Container
∗
1.2. Consumer fuel container incident scenarios There have been several documented consumer portable fuel container incidents that illustrate different fuel container incident scenarios. Stevick et al. (2011) report investigating incidents involving portable fuel containers that “have been left standing open with either their nozzles removed or kept un-capped for weeks or months before incidents.” They show evidence of one plastic fuel container that they say has experienced an explosion that caused the container to tear open. Hasselbring described an incident that occurred when a five-gallon container was being tilted to pour gasoline onto a small fire in order to increase the fire size. The result, according to Hasselbring, was a container explosion splattering the victim with burning fuel and causing burn injuries over 65% of his body. St. John (2017) described a tragic incident in which a young girl suffered fatal burn injuries when her father started pouring a mixture of
Corresponding author. E-mail address: [email protected] (A. Rangwala).
https://doi.org/10.1016/j.jlp.2019.06.006 Received 14 March 2019; Received in revised form 6 June 2019; Accepted 6 June 2019 Available online 08 June 2019 0950-4230/ © 2019 Published by Elsevier Ltd.
Journal of Loss Prevention in the Process Industries 61 (2019) 249–254
A. Rangwala and R. Zalosh
2. Flame mitigation experiments
gasoline and heavy petroleum distillate from a two-gallon portable container onto a fire in a fire pit. The container did not have a nozzle attached. St. John conducted forensic testing that produced flame jet lengths “in excess of 2 m” from the mouth of open fuel containers. These and other incidents show that portable fuel container flashbacks have occurred with both open containers and in containers with attached spouts. External ignition of the flammable vapours +in some cases causes the container to explode, and in other cases the container remains intact but becomes sufficiently pressurized to generate lengthy flame jets. None of the containers had installed flame arresters. This is in contrast to the U.S. Department of Transportation approved metal safety cans that are required to have both a flame arrester and a pressure relieving device (U.S. CFR §1926.152(a)(1)).
2.1. Butane-air mixture representation of fuel vapor mixture In choosing this method of testing, we considered using gasoline vapor directly however abandoned this idea for a few reasons. First, the composition of gasoline vapor is highly variable: depending on time of year, geographic location, blend, etc. This presents a challenge in developing an experimental method that is consistent and repeatable across multiple tests over a long period of time. Any small change in the characteristics of the gasoline can alter the flammability test results. Second, the use of gasoline vapor directly presents a second challenge in collecting the vapor for testing. If liquid is simply placed in the bottom of a PGC, the concentration of flammable vapor within the PGC is dependent on multiple factors (angle, temperature, time, etc.) (Elias et al. 2010; Elias, 2011). Again, this makes it difficult to perform consistent tests across multiple samples. A representative fuel/air mixture to model the flammability characteristics of gasoline vapor is therefore necessary. Gasoline container headspaces are composed of complex mixtures of hydrocarbons and ethanol, with the compositions varying with geographic region and season of the year, as well as the grade of gasoline. An example of some May 1999 gasoline samples in California reported by Harley et al. (2000) showed that approximately 50 wt percent of the regular grade gasoline headspace consisted of n-butane, n-pentane, and i-pentane. The higher-grade gasoline samples had slightly less of these components, with approximately equal amounts of n-butane and n-pentane. Since the other components, other than ethanol, had significantly higher molecular weights, the proportions of butane and pentane would be correspondingly higher on a volume percent or mol percent basis. The challenge a particular flammable vapor poses to a flame mitigation device depends on the vapor burning velocity and either quenching distance or Maximum Experimental Safe Gap (MESG). Published values of these flammability parameters are shown in Table 1 for n-butane, n-pentane, a nominal 100-octane gasoline formulation, and ethanol. The n-butane values are within 13% of the values for the other vapours, and is within 5% for MESG, which at least some organizations use as the parameter to determine applicability of flame arresters to gasoline and other flammable vapours. Since n-butane is both widely available and convenient to use for generating a readily repeatable representation of gasoline vapor headspace, it was selected as the fuel for Portable Fuel Container (PFC) flame mitigation device effectiveness testing. The use of a butane/air mixture also allows for the burning velocity to be varied by adjusting the concentration of butane in the mixture. If it is desired to test a different gasoline blend, this is easily accomplished in the laboratory by adjusting the concentration of butane in the mixture to match the burning velocity of the desired gasoline vapor. This allows for the testing of multiple fuel compositions using the same test apparatus. The effect of weathering on the fuel sample is also a consideration in this testing method. As gasoline ages, the composition of the headspace changes and the relative concentration of unsaturated hydrocarbons increases. These unsaturated hydrocarbons have higher burning
1.3. Industrial flammable liquid container scenarios and requirements Industrial flammable liquid container incidents tend to fall into two categories, both different than the consumer incidents described above. One category is the sustained fire exposure to stored closed containers. The safety can construction requirement to have a “spring-closing lid and spout cover designed to safely relieve internal pressure when exposed to fire” (NFPA 30-15) is well suited for this scenario. The second category of industrial incidents is when the container is used to dispense some special liquid for processing or a solvent for cleaning equipment and fixed surfaces. Ignitions in the second category lead to potential flashbacks that can challenge the container flame arrester. U.S. certification of these industrial safety cans include flashback requirements but not necessarily as stringent as the following flashback mitigation testing objectives for consumer fuel containers. 1.4. Flame mitigation testing objectives Both the portable consumer fuel container manufacturers and the cognizant U.S. government regulatory agency (the Consumer Product Safety Commission) acknowledge that dangerous consumer actions exposing flammable vapours to flames and other ignition sources cannot be totally eliminated and therefore support efforts to develop PFC flame mitigation devices. These organizations have been working through the ASTM voluntary standards organization to fund and oversee the development of a suitable test method to assess the effectiveness and reliability of installed flame mitigation devices. One major objective of portable fuel container Flame Mitigation Device (FMD) testing is to determine the effectiveness of the FMD in configurations that account for the incident scenarios described above and potential variations that might present even greater challenges. The flame arresting challenge depends on the flame speed approaching the FMD and the flammable mixture burning velocity and quenching distance within and on the other side of the FMD. Since these parameters depend on both the fuel vapor composition/concentration and the presence of potential flame acceleration conditions, the testing arrangement should entail a repeatable but representative fuel vapor concentration and a realistic high-challenge approaching flame speed conditions that include confinement associated with flame propagation through a container spout. Table 1 Comparison of vapor flammability properties. Property
n-Butane
n-Pentane
Gasoline (100 octane)
Ethanol
Laminar Burning Velocitya (cm/s) Quenching Diameterb (mm) Max Exp Safe Gap (MESG)c (mm)
45 3.4 1.066
46 2.4–3.4 1.016
40 No Data No Data
41 3.0 1.016
a b c
Burning velocity data from NFPA 68 Table D.1, except ethanol data from Konnov et al. (2011). Quenching diameter data from Grossel (2002) Table 5-3. MESG data from 33CFR Part 154 Appendix B (2002). 250
Journal of Loss Prevention in the Process Industries 61 (2019) 249–254
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Fig. 1. FMD test setup for tests with spout (a) and without spout (b). Dimensions in mm.
spout mounted in the test stand. The FMD is not visible because it is installed in the neck of the PFC such that it can prevent flame propagation into the PFC with or without the attached spout. The aluminum foil deflagration vent installed on the cutoff bottom of the PFC is not visible in this side view of the mounted PFC. The polycarbonate ignition/flame propagation tube is visible in the upper right area of the photograph. The effectiveness of the FMD is easily discerned by seeing if the aluminum foil deflagration vent bursts after ignition (because of flame propagation through the butane-air mixture in the cutoff PFC). A video camera records the test results to confirm the presence of flame in the igniter/flame propagation tube and to provide a visual record of the test result.
velocities compared to saturated alkanes and may require further testing with a modified representative fuel mixture.
2.2. Experimental setup and procedure The FMD test configuration is shown in Fig. 1a for tests with the attached spout and in Fig. 1b for tests without the spout. Only a cut-off portion of the PFC with installed FMD is used in the tests so that a makeshift deflagration vent can be installed on the cut-off PFC. The butane-air mixture is made using mass flow controllers and tubing leading to a 50 mm diameter, 120 mm length, ignition and flame propagation tube attached to either the spout (a) or PFC (b). The air and butane mass flow controllers are programmed to produce a 2.83 vol percent butane in air mixture, corresponding to an equivalence ratio of 0.90. This mixture flows through the igniter tube and cutoff portable fuel container and into an exhaust tube leading to a gas analyzer as shown in Fig. 1. When the gas analyzer reading confirms that the desired butane concentration PFC has been reached in the igniter tube and the PFC, the exhaust line and gas supply line are disconnected in preparation for firing the approximately 10 J igniter in the transparent igniter/flame propagation tube. A close up of a butane-air mixture flame propagation in the igniter tube is shown in Fig. 2. The average flame speed or the speed of the flame after a run up across the length of the igniter tube equals 5 m/s. the flame speed was measured with a high-speed 5000 frames per second video camera. Fig. 3 is a photograph of a PFC with an installed FMD and attached
3. Concept flame mitigation devices A wide variety of concept FMDs have been tested using the apparatus and procedure described above. Figs. 4 and 5 show some examples of these FMDs illustrating how they are inserted in the PFC neck. The FMDs shown on the left and right in Fig. 4 are both flexible elongated plastic meshes with rigid plastic support frames. The FMD in the center of Fig. 4 is a rigid plastic mesh shaped into a cup/dome, while the FMD on the left of Fig. 4 is a cup shaped metal mesh. In the center of Fig. 5 is a single piece rigid plastic mesh, while Fig. 5 right shows a rigid plastic frame with a flexible composite carbon fiber mesh. 251
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Fig. 2. Butane air flame propagation observed using a high-speed camera (5000 frames per second). The average flame speed is 5 m/s for a butane-air mixture at equivalence ratio of 0.9.
the basic flame quenching design. In the case of the unsuccessful metal mesh FMD, it appears that the basic mesh size is more open than the plastic mesh designs that were successful in this test. Since several of the concept FMDs are composed of combustible materials, there is concern about possible thermal degradation if these FMDs need to withstand multiple transient flame exposures. Therefore, five concept designs have been subjected to up to five flame propagation tests when installed in a PFC. Results are shown in Fig. 7. Two FMDs experienced significant mesh melting without any flame mitigation success. Another FMD experienced deformation that prevented successful mitigation after the first test. Two other FMDs, labelled Designs 3 and 4 in Fig. 7, successfully prevented five flame propagations into the PGC without experiencing any visible degradation. Design 3 is composed of a flexible sock-like fire-resistant fabric, while Design 5 consists of a rigid polymer with rows of approximately 1-mm square openings. Some of the successful FMD prototypes have also been tested by at least one PFC manufacturer for the prevention of flashbacks in container spills near small flames that produce flame jetting in the absence of an installed FMD in the container. The FMDs that were successful in the butane-air mixture tests described above were also successful in preventing flame jetting in tests similar to those described by St. John (2017). In fact, all six cylindrical mesh and screen disk FMDs used to prevent flame jetting in tests described by Stevick et al. (2011) were successful. However, the flame speed reported by Stevick et al. for the flame jetting tests was only 0.4 m/s, whereas the flame speed in the ignition tube tests described here is about 4 m/s, which is within 10% of the flame speed corresponding to the 0.45 cm/s butane burning velocity multiplied by a burned gas expansion ratio of 8. This indicates that the butane-air mixture flame propagation test described here is a more stringent challenge than the fuel spill simulation flame jetting tests.
Fig. 3. Portable Fuel Container mounted in Flame Mitigation Device test stand.
Many other versions of these types of concept FMDs have also been tested.
4. Flame mitigation device test results Fig. 6 shows two video frames of a test with a candidate FMD installed in a PFC that did not prevent flame entry into the interior butane-air mixture. The large vented flame is an obvious manifestation of the failed FMD effectiveness. Table 2 shows the results of the tests with the concept FMDs shown in Figs. 4 and 5. Four of these concept FMDs successfully prevented flame propagation into the PFC while the other two did not. In the case of the two similar design flexible elongated plastic meshes, the shorter version successfully prevented flame propagation, but the longer version was unsuccessful, probably because a small gap formed at the junction of the two half-sections. This illustrates the need for a successful FMD to have careful and robust fabrication details in addition to
5. Other requirements for portable fuel container FMD A commercially viable flame mitigation device for a portable fuel container must have certain fuel compatibility and durability characteristics besides being able to prevent flame propagation in a laboratory test. Three specific characteristics are:
• Allowing unrestricted fuel flow into and out of the container • Withstanding frictional contact with refuelling station dispensing nozzles
Fig. 4. Examples of early versions of FMDs in fuel container necks. 252
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Fig. 5. Additional examples of concept FMDs.
• Withstanding
prolonged exposure to common fuel formulations without significant degradation
Table 2 Results of tests on examples of concept FMDs.
The authors and the WPI Combustion Laboratory staff have been working with the ASTM F15.10 Subcommittee to develop appropriate test methods for these FMD compatibility and durability characteristics. The flow restriction tests entailed measuring the flow times for 10 gpm (38 lpm) nominal flows into the PFC and inclined platform gravitational outflows. Four of the five FMDs were able to accommodate these flows with less than 15% reductions in the corresponding flows without any FMD in the PFC. The frictional durability test involved 25 repeated controlled insertions of a fuel dispensing nozzle into and out of the FMD equipped PFC. Two of the five concept FMDs experienced sufficient mesh degradation during these repeated insertions to prevent them from being able to successfully prevent flame propagation when tested with the method described in Section 2 of this paper. The FMD fuel exposure test conditions were daily exposures of the FMD to wetting by a standard ethanol containing gasoline formulation, and continuous 90-day exposure to the fuel vapor. Four of the five concept FMDs successfully survived the prolonged exposure to a 15% ethanol formulation (CE 15) without any apparent deterioration, but only two of the five successfully withstood a similar exposure to an 85% percent ethanol formulation (CE 85).
Figure with FMD
Description
Prevent Flame Entry into PGC?
Fig. Fig. Fig. Fig. Fig. Fig.
Flexible elongated plastic mesh Rigid plastic mesh dome Flexible elongated plastic mesh Cup shaped metal mesh Rigid plastic mesh cylinder Flexible composite carbon fiber mesh
Yes Yes No No Yes Yes
4 4 4 5 5 5
Left Center Right Left Center Right
Laboratories are members of the Subcommittee actively participating in the standard development, these organizations should be prepared to conduct the testing required to implement the standard. Furthermore, representatives of the Consumer Product Safety Commission are also active in this process so that the CPSC can simultaneously develop its position on any appropriate federal regulatory considerations in the sales and use of PFCs for the U.S. consumer market.
7. Conclusions A Portable Fuel Container Flame Mitigation Device test method has been developed to determine the effectiveness of installed FMDs in preventing the propagation of a butane-air mixture flame into the PFC. The butane-air mixture serves as a surrogate for the types of hydrocarbon-ethanol fuels commonly used in contemporary PFCs. The test method provides a high challenge to successful prevention of flame entry into the PFC, but at least two FMD designs have demonstrated capability to successfully prevent five repeated flame propagation tests. Prolonged fuel exposure, unrestricted fuel flow, and dispensing nozzle friction durability tests have also been developed for FMD equipped PFCs. An ASTM standard is currently under development delineating versions of the flame propagation, fuel exposure, and fuel flow and dispensing nozzle tests.
6. Test standard development approach and status ASTM Subcommittee F15.10 has been writing a draft “Standard Specification for Flame Mitigation Devices on Portable Fuel Containers.” The draft standard describes the flame propagation test described in Section 2 and the three types of fuel compatibility and mechanical durability tests described in Section 5. The draft standard requires a 5-gallon (20 L) capacity prototype containers with installed FMDs to pass specified versions of these tests. After the draft standard has been voted upon and adopted as an official ASTM standard, it will serve, along with ASTM F852, as the voluntary consensus standard applicable to Portable Fuel Containers sold in the U.S. Since representatives of Nationally Recognized Testing
Fig. 6. Video frame images before and after flame is vented from PFC. 253
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Fig. 7. Five FMDs after flame mitigation testing.
Acknowledgements
Gardiner, D.M., Bardon, M.F., Pucher, G., 2008. An Experimental and Modeling Study of the Flammability of Fuel Tank Headspace Vapors from High Ethanol Content Fuels. Nexum Research Corporation, Mallorytown, Canada. Grossel, S., 2002. Deflagration and Detonation Flame Arresters. AIChE Center for Chemical Process Safety. Harley, R.A., Coulter-Burke, S.C., Yeung, T.S., 2000. Relating liquid fuel and headspace vapor composition for California reformulated gasoline samples containing ethanol. Environ. Sci. Technol. 34 (19), 4088–4094. Hasselbring, L.C., 2006. Case study: flame arresters and exploding gasoline containers. J. Hazard. Mater. 130, 64–68. Konnov, A.A., Meuwissen, R.J., de Goey, L.P.H., 2011. The temperature dependence of the laminar burning velocity of ethanol flames. Proc. Combust. Inst. 33 (1), 1011–1019 2011. NFPA 30, 2015. Flammable and Combustible Liquids Code. National Fire Protection Association. NFPA 68, 2018. Standard on Explosion Protection by Deflagration Venting. National Fire Protection Association. Okamoto, K., Watanabe, N., Hagimoto, Y., Miwa, K., Ohtani, H., 2009. Changes in evaporation rate and vapor pressure of gasoline with progress of evaporation. Fire Saf. J. 44, 756–763. St. John, A., 2017. The science of flame jetting. NFPA J September-October 2017. Stevick, G., Zicherman, J., Rondinone, D., Sagle, A., 2011. Failure analysis and prevention of fires and explosions with plastic gasoline containers. J. Fail. Anal. Prev. 11455–11465. Vaivads, R., Bardon, M.F., Rao, V.K., Battista, V., 1994. Flammability of alcohol-gasoline blends in fuel tanks. Int. Assoc. Fire Saf. Sci. 4, 575–586.
The authors gratefully acknowledge the financial support and guidance from the ASTM F15.10 Subcommittee. They also want to acknowledge the excellent work of various WPI students and research staff in setting up and conducting the testing described here. References ASTM F852-99, 2006. Standard Specification for Portable Gasoline Containers for Consumer Use. ASTM. CFR Title 33, Part 154, 2002. Appendix B, Standard Specification for Tank Vent Flame Arresters, Code of Federal Regulations. Elias, B.E., Zalosh, R.G., Rangwala, A.S., 2013. Portable gasoline container headspace flammability. Fire Saf. J. 58, 248–257. Elias, B.E., Zalosh, R.G., Rangwala, A.S., 2010. Gasoline container vapor space flammability. In: 8th International Symposium on Hazards, Prevention, and Mitigation of Industrial Explosions, Yokohama, Japan Sep 5-10, 2010. Elias, B.E., Zalosh, R.G., Rangwala, A.S., 2011. Conditions affecting external flame propagation into a portable gasoline container: a summary of test methods and experimental findings. In: Eastern States Fall Technical Meeting, Storrs, University of Connecticut, Oct 9-12, 2011. Elias, B., 2011. Hazard Assessment of Portable Gasoline Container Flammability, MS Thesis. Worcester Polytechnic Institute.
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