Hydrogen and CNG Stations – A New Risk Comparison
Based on the work of A. Tchouvelev, R. Hay and P. Benard inComparative Risk Estimation of Compressed Hydrogen and CNG Refuelling Options.

Quantifying the risks from hydrogen fueling stations is a vitally important activity. As a benchmark, the comparison to risks from compressed natural gas (CNG) fueling option, will aid the development of codes and standards based on research and data as well as stakeholder education campaigns. 

The Canadian Hydrogen Safety Program recently finished a significant new project for the Codes & Standards Working Group of the Canadian Transportation Fuel Cell Alliance. The project,Comparative Quantitative Risk Estimation of Hydrogen and CNG Refuelling Options, was a comprehensive risk analysis of various hydrogen sourcing and fueling site configurations. The clear conclusion of the project is that hydrogen fueling is as safe as, or safer than, CNG fueling. 

The researchers conducted parallel analysis of hydrogen and CNG stations using quantitative risk assessment tools for a wide range of safety-critical issues. Using CNG as a basis for comparison gave the researchers a reference with established data about the public’s level of risk aversion. Hydrogen leak scenarios from sources including tube-trailer delivery vehicles, on-site reformers and electrolysers, and storage tanks were examined representing the concerns that provide key input to design and public acceptance decision making. 

In 2005 TIAX released a Failure Mode and Effects Analysis (FMEA) study of hydrogen fueling options compared to a CNG fueling option. The TIAX study provided good guidance on the risks of various hydrogen technologies vs. CNG technology. The Canadian Hydrogen Safety Program study extended the comparison beyond the FMEA’s qualitative analysis with a detailed quantitative comparison of “stand-out” elements that are either technology or fuel related. The TIAX study came to several important conclusions that are worth repeating:

  • None of the hydrogen scenarios considered presented high risk and generally all the hydrogen fueling options considered were at par with a CNG fueling option;
     
  • In terms of medium risk, CNG fueling presents less risk due to the simplicity of the system and generally lower pressure;
     
  • In terms of medium risk, reformer technology is marginally riskier due to higher complexity arising from the need to deal with two fuels, methane and hydrogen, a higher process temperature and a higher internal inventory of gases;
     
  • Electrolyser-based and tube trailer options are approximately at par in terms of medium risk.

The Canadian Hydrogen Safety Program study reached a similar suite of conclusions. They found that producing hydrogen on-site by electrolysis presents a lower location-specific individual risk (LSIR) than producing hydrogen on-site by steam methane reforming (SMR). This is thought to be due to the complexity of the installation in the SMR case and because both hydrogen and natural gas are present in SMR. 

Whether the hydrogen is sourced on-site or off-site, the LSIR is almost the same. However, on-site electrolysis appears to be less risky than tube trailer delivery, which in turn is safer than on-site steam methane reforming within the scope and assumptions of the considered scenarios. 

A comparison of the relative risk associated with hydrogen and natural gas storage shows that a hydrogen storage facility presents a marginally lower (within 20%) risk compared to an identical CNG storage. This conclusion is based on the hazard from the thermal effects of an accidental horizontal-jet release from storage connecting piping. Regarding storage venting, a CNG storage facility may require either a larger clearance than an identical hydrogen storage facility or a higher vent stack to achieve the same level of thermal radiation from a vertical flare at human height. 

A final conclusion is that an electrolysis fueling option that includes compressed hydrogen storage presents the lowest risk among the fueling options that were considered including a CNG station of equal fueling capacity to provide equivalent travel mileage.

Authors
A. Tchouvelev - A.V.Tchouvelev & Associates Inc., 6591 Spinnaker Circle, Mississauga, ON Canada L5W 1R2

R. Hay - Tisec Inc., 2755 Pitfield Boulevard, Montreal, QC Canada H4S 1T2

P. Benard - Hydrogen Research Institute, Université du Québec à Trois-Rivières, 3351 Boulevard des Forges, CP 500, Trois-Rivières, QC Canada G9A 5H7

DOE Hydrogen Program Merit Review: Safety-Related Session Summary
David Mann, National Hydrogen Association

From May 15-18, 2007 the US hydrogen industry came together to evaluate our national progress on breaking down the barriers to the widespread development of a hydrogen economy. Approximately 300 projects were showcased at the Crystal City Marriott in Arlington, Virginia at the US Department of Energy Hydrogen Program’s Annual Merit Review. The Merit Review opened with a plenary session providing an overview of all of the Department of Energy’s hydrogen activities. Speakers represented the offices of Energy Efficiency and Renewable Energy, Fossil Energy, Nuclear Energy, and Science. 

Safety, Codes and Standards
Dr. Milliken spoke about the value and need for codes and standards and the general challenges facing their creation and adoption. Dr. Milliken felt progress was being made, giving examples such as the completion of a technical reference for hydrogen compatibility, a compendium of permitting tools, the development of a hydrogen safety panel, and a hydrogen incident database. DOE plans on continuing recent sensor-related activity, publishing a best-practices manual, creating hydrogen quality specifications, and increasing their emphasis on early market activities, particularly safety and portable fuel cells. The FY08 budget request of $16 million includes a doubling of funds from $1.5 million to $3 million for sensors. This accounts for the bulk of the budget request increase over the FY07 appropriation of $13.8 million. 

Education
Dr. Milliken spoke about the hydrogen program’s education activities. She indicated good progress with the completion of a web-training course for first responders and the creation of the H2IQ campaign. DOE will also restart middle and high school educational activities. Dr. Milliken pointed to upcoming activities as being vital, including the NHA’s H2U student design competition and the H2 and You campaign. They plan on ramping up first responder training, developing training for code officials, and issuing new solicitations. The education budget is requested at double current levels for FY08 with most of that being targeted to early deployment activities.   

Manufacturing R&D
Dr. Milliken spoke on Manufacturing R&D. The largest challenge is that the technology to be manufactured is still developing. The budget is quite small for this new program, but will be increasing to $5 Million for FY08 and a solicitation is expected in summer 2007.

Market Transformation
Dr. Milliken closed the session with a discussion of Market Transformation. She highlighting the difficulties hydrogen products face. Dr. Milliken said that the Energy Policy Act authorizes DOE to pursue early adoption and that last month DOE put together a meeting with federal procurement managers and hydrogen industry folks to exchange knowledge and begin a federal early adoption program. The recent DOE RFI is another sign of activity on this front. More information can be found here:http://www.hydrogen.energy.gov/news_markets.html. 

Dr. Milliken’s full presentation is available on the Department of Energy website at:http://www.hydrogen.energy.gov/annual_review07_plenary.html. 

Posters and presentations from other meeting sessions are available on the main page of the 2007 Annual Merit Review Proceedings at:http://www.hydrogen.energy.gov/annual_review07_proceedings.html.

Results of the ICC Final Action Hearings
Nine new hydrogen-related proposals approved regarding metal hydrides, vehicle fueling, liquid hydrogen and more
Patrick Serfass , National Hydrogen Association

From May 22-26, 2007, the Final Action Hearings for the International Code Council family of codes was held in Rochester, NY. Those hearings ended the 2006-07 cycle for I-Code revisions. The results are reported below.

What’s New? How is this relevant? Please read on below.

2006/07 ICC Results for Hydrogen-related Proposals 

Code ProposalInformal DescriptionPublic Hearing ResultFinal Action Hearing Result

F53Lithium Metal Polymer batteries (PDF)DAMPCI

F54Required automatic status monitoring of lead acid battery room ventilation systems (PDF)D-ASFAS

F154Vehicle overpressure protection (PDF)ASAS

F155Indoor fast-fill dispensing (PDF)DD

F156Electrostatic discharge for fueling pads (PDF)DAMPC1

F157Consistent 'listing' of lighter-than-air gas detection systems (PDF)AMAM

F172Addressing hydrogen cylinders stored in outdoor cabinets (PDF)DD

F175Possible diking around above ground LH2 storage (PDF)DWP

F191Movement of LH2 language and new LH2 tank requirements from CGA (PDF)AMAM

F193Telecomm cabinets and transfer switches near outdoor hydrogen cabinets (PDF)DD

F194Guidance for metal hydride systems (PDF)ASAS

F229New requirements for indoor hydrogen storage (PDF)DWP

M56Ventilation requirement moved from exhaust to ventilation (PDF)DD

FG54H2 Piping-Concealed Locations (PDF)ASAS

FS37
Fire barrier definition (PDF)ASAS

Legend:
AS - Approved as Submitted
ASF - Approved as Submitted by Assembly Floor Action at Code Development Hearing
AM - Approved as Modified by the Code Committee at Code Development Hearing
AMF - Approved as Modified by Assembly Floor Action at Code Development Hearing
AMPC1 – Approved as Modified by Public Comment #1
D - Disapproved
DF - Disapproved by Assembly Floor Action at Code Development Hearing
WP - Withdrawn by Proponent

What’s New in the International Codes for Hydrogen?
For starters, all the new language in proposals that were approved at the Final Action Hearings (F53, F54, F154, F156, F157, F191, F194, FG54 and FS37) is now a part of the I-Codes as a published supplement to the relevant code. For example, the language in F191 is now in the supplement to the International Fire Code and the language in FG54 is in a different supplement to the International Fuel Gas Code. Every alternate cycle, several supplements are published instead of each entire code book. (The result of the next 07-08 cycle will be to publish full editions of each International Code.) However, in the end, the effect is mostly the same: this language is now in the codes. 

What’s New:

  • With F154, there is now a slightly improved requirement for hydrogen dispensers that protects the hydrogen vehicle’s fueling system and harmonizes the language with current requirements from the Society of Automotive Engineers (SAE);
     
  • With F156, there is now a new requirement for the pad that you drive onto at a fueling station that will make sure to dissipate any static electricity built up by driving the vehicle before you even open your door to fuel; 
     
  • With F191, there are new requirements for the construction of liquid hydrogen tanks; 
     
  • With F194, metal hydride storage systems will now be recognized logically as regular, flammable gas systems which maintains the same level of safety, but allows for easier approval of metal hydride systems, hopefully leading to increased use; 
     
  • With F54, battery room ventilation systems will now be “supervised” by one of a variety of signals to inform someone that the air in the battery room has a concentration of hydrogen greater than 1 percent; and finally, 
     
  • With F157, there is an expanded ability for gas detection systems that are listed OR approved to now be used in a variety of applications, expanding the number of products that can be used to detect certain gases.

More detail on each of these follows. For exact code language and proposals, please refer to the links in the table above.

F154-06/07: "Vehicle overpressure protection"
Proponent: Thomas Joseph, Chair, Hydrogen Industry Panel on Codes

This newly-approved language resets the level at which the overpressure system on the dispenser side of the vehicle fueling system should activate to prevent overpressure of the vehicle fuel system. The level (“140 percent of the service pressure of the fueling nozzle it supplies”) was chosen to be consistent with overpressure levels as determined by SAE. At the time of publication, SAE has recently tweaked their overpressure level from 140% to 138% to be consistent with other requirements. Safety-wise, this is a negligible change however it helps to harmonize the SAE and ICC requirement for overpressure protection. 

[Go back to What’s New]

F156-06/07: "Electrostatic discharge for fueling pads"
Proponent: Thomas Joseph, Chair, Hydrogen Industry Panel on Codes

This new language improves the safety of both hydrogen and gasoline vehicle fueling by making sure that the static electricity built up by driving the vehicle is immediately dissipated when the vehicle drives onto the fueling pad, and BEFORE the driver even opens the door. Fueling station builders have a choice with this language of making the fueling pad out of concrete or of any approved material that has a resistivity of less than 1 megohm.

If you drive a gasoline car, you might have noticed that most gasoline fueling stations already have concrete pads because it is a long standing recommended practice of the American Petroleum Institute. (The concrete not only helps to dissipate static electricity, but it helps to prevent petroleum fuels from contaminating groundwater. Asphalt is porous and petroleum based fuels can both dissolve and penetrate it.) Therefore, there is little or no effect to the current gasoline practices. However, this puts the already common practice of using concrete into code and also sets an improved precedent for new hydrogen fueling stations.

If you do not want to use concrete, approved materials could be ones that meet either of the following standards:

[Go back to What’s New]

F191-06/07: "Movement of LH2 language and new LH2 tank requirements from CGA"
Proponent: Larry Fluer, Fluer, Inc., representing Compressed Gas Association

This code change proposal has three main parts to it, all related to liquid hydrogen: new definitions, moving requirements among chapters and new liquid hydrogen tank construction requirements.

This new language adds new definitions for "bulk liquefied" and "bulk compressed" gas systems where specific details surrounding such installations can be found.

Other parts of this approved language moves the requirements for liquid hydrogen from Chapter 32 (cryogenic fluids) to Chapter 35 (Flammable Gases and Flammable Cryogenic Fluids). This is important for consistency since there are no other fuel-specific requirements in Chapter 32. Therefore, liquid hydrogen-specific requirements don’t belong there either. Chapter 35 has the fuel-specific language in it to account for things like the different properties of fuels. The liquid hydrogen requirements have been moved there.

Finally, the Fire Code now has new requirements for liquid hydrogen tank construction that are harmonized with the newly published CGA Standard H-3-2006 on Cryogenic Hydrogen Storage. According to the proponent, the more specific minimum design requirements established by Section 3506.3 coupled with the general requirements of Chapter 32 applicable to all cryogens (see paragraph above) improve the code resulting in greater consistency and an increase in public safety.

[Go back to What’s New]

F194-06/07: "Guidance for metal hydride systems"
Proponent: Larry Fluer, Fluer, Inc., representing Compressed Gas Association

This proposal adds important language relevant to metal hydrides. In short, this should help to accelerate the installation and approval of metal hydride systems in the marketplace due to the fact that metal hydride systems can now (again) be treated in many ways as regular gaseous hydrogen systems.

It is interesting to note that part of this language had been adopted into the fire code before (during the 04-05 cycle), and was deleted during the last (05-06) cycle. Now, this improved language has been approved during the 06-07 cycle which just ended in Rochester in May.

The new code language was proposed by the Compressed Gas Association (CGA) in an effort to bring the different-minded parties to consensus in a manner that recognizes the presence of these unique systems, and to place fundamental requirements in the code to address their use. This language requires that the metal hydride container be treated as a flammable gas container and not with any special treatment to the materials that make up the metal hydride mixture. This is considered a safe practice because metal hydride tanks are designed to never allow the metal hydride material to leave the container—only the hydrogen goes in and out.

[Go back to What’s New]

F54-06/07: "Required automatic status monitoring of lead acid battery room ventilation systems"
Proponent: Lynne M. Kilpatrick, Fire Department, City of Seattle, WA

This change requires that the ventilation systems for battery changing rooms have supervision by an "approved central, proprietary, or remote station service" or the activation of "an audible and visual signal at a constantly attended on-site location." These alarms are automatically activated when there is more than 1% of hydrogen in the room. According to a discussion with the proponent, this language only applies to stationary lead-acid battery systems with an electrolyte capacity >50 gal. and now requires status monitoring of the ventilation system. This is typically accomplished with a vane-type paddle in the duct that changes position when there is no airflow and activates a position switch that can be monitored by the fire alarm system. Although this change will increase the cost of new installations, cost may not increase by much since the smoke detectors already required (by 608.8) will make sure a fire alarm system is present and a fire alarm circuit is nearby.

[Go back to What’s New]

F157-06/07: "Consistent 'listing' of lighter-than-air gas detection systems"
Proponent: Greg Rogers, South Kitsap Fire & Rescue, representing ICC Joint Fire Service Review Committee

The language expands the ability to use new gas detection systems. Specifically, it changes gas detection systems from requiring to be "approved" (approved by the permitting official) to requiring that they be "listed or approved." Systems that are certified by a third party are often “listed.” The proponent says this change is needed because similar sections in other parts of Chapter 22 also require gas detection systems to be "listed" (See 2208.2.2 which deals with natural gas motor fuel dispensing facilities and 2209.2.2 which deals with hydrogen motor fuel-dispensing and generation facilities). Therefore, requiring that gas detection systems be “listed OR approved” will allow a greater number of gas detection systems to be used; it will expand the ability to install new technologies and therefore open the market for these devices; and it makes the language more consistent with other parts of the code.

For a history of the results of past ICC hearings see the following articles:

ISO/TC 197 WG13 Hydrogen Detectors Holds Meeting in Seoul, Korea
Karen Hall, National Hydrogen Association

ISO TC 197 WG 13, which is preparing an international standard for hydrogen detection apparatuses where multi-level sensing is required, met on June 8 and 9 in Seoul, Korea.

The Working Group (WG) spent the two days reviewing and resolving comments received from member countries on the ISO Committee Draft 26142: Hydrogen Detection Apparatus. The meeting focused on the technical comments with the potential to require discussion and resolution. Additional comments will be resolved for the next meeting.

A representative from a testing lab in Germany, as well as an expert from IEC TC 31 from Italy attended the meeting to help resolve comments and improve the document. They were a valuable addition to the discussion. Also represented were: Canada, Japan, South Korea, and USA.

Key issue: Japan continues to press for a lower detection limit of 100 ppm. All other delegates present want an option for up to 1000 ppm. The group spent most of the meeting on this point, and the associated tolerances to the results of testing the sensors at four points in or above the flammability range. The standard applies to refueling stations as well as other stationary applications where the user desires the ability to monitor hydrogen concentrations.

Japan is mainly concerned with detection apparatuses installed some distance from outdoor refueling stations, where the concentration of hydrogen at the detector may be significantly lower than the concentration near the leak. Other experts want the flexibility to have manufacturers declare the lower detection limit from 0-1000 ppm, and have the first test point at that declared value.

Representatives from Canada, Germany, Italy and the U.S. noted that no action would be required at or near 100ppm, and that a requirement to select hydrogen at this level would result in many sensor technologies being excluded from applications covered by the standard. In addition, increased resulting false positive readings may actually compromise the safety of the system. Those from Japan, on the other hand, presented data of fuel stations with settings at 500 ppm, and even less in some cases, as well as a brochure of electrochemical sensors capable of detecting hydrogen at 100 ppm, reiterating that they share the same philosophy of finding the proper combination of the performance of detectors required based on a wide range of installations and locations, and available detection technologies.

As a compromise, the Working Group agreed to work on the language to allow a range of lower detection limits, as declared by the manufacturer, so that the resulting standard would be more usable for a variety of stationary applications where continuous monitoring and multi-level sensing is desired.

Although the WG worked very hard, the time was insufficient to resolve all the comments received. Therefore many technical issues resulting from the CD comments are being addressed through homework assignments in advance of the next WG13 meeting, which will take place in conjunction with the ISO Plenary meeting in Italy in early November.

ISO TC 197 WG 12 Meets in Seoul, Korea
Karen Hall, National Hydrogen Association

Professor Dr. Yasuo Takagi, the Convenor of WG12, opened the meeting and welcomed all experts and delegates to the working group 12 meeting on June 6-7 in Seoul, Korea. ISO TS14687-2:Hydrogen Fuel Quality Specification has been approved by ISO TC 197 for publication. The working group is now working toward a Draft International Standard, which the experts agree will take a couple years to develop. Long-term R&D projects are required to fill in the data gaps in order to progress from a Technical Specification to a Draft International Standard. In addition, it is desirable to address the concerns of all stakeholders of the proposed International Standard, including fuel providers and station operators. The development of test methods was one issue raised by many stakeholders. In addition long-term research on the effects of non-hydrogen constituents in hydrogen fuel is required to validate or refine the values that are currently defined in the Technical Specification. 

Japan presented interim results of accumulation behavior of some critical non-hydrogen constituents, as well as their plans for testing, which use the same conditions and cells as the data developed over 2 years ago. A factor of 1/500 is being used in determining the recommended threshold levels of constituents causing irreversible or partially reversible performance loss. This factor is proposed by Japan and is based on a desired fuel efficiency of 99.8%. North America prepared and submitted a position statement on this issue in February 2005. Karen Hall recommended the WG review those issues in advance of the testing in an attempt to address the issues raised by the North American experts.

Japan, Korea, and the JRC/FCTES QA will examine the test protocol presented by the North American team at the WG12 meeting in November 2006 and consider adoption of the protocol as presented or amended at the next WG12 meeting. The objective of adopting a protocol is to enable testing to proceed on a common basis among all WG12 participants and to allow WG12 to utilize the laboratory capabilities and expertise among all of its members most efficiently. The adoption of a common protocol does not preclude use of specific test procedures needed for specific tests. Changes and exceptions from the protocol made in such cases should be thoroughly documented. Much discussion on whether single cell tests are meaningful. It was agreed WG 12 should continue forward, and the protocol could be validated in parallel. 

FCTestNet will send Working Group 12 the data reporting format the European Commission is using for consideration so all parties can use the same format. The Working Group should also determine a baseline for the test cells to be used. 

Japan has started a project to engage the fuel providers in the issue of hydrogen fuel quality. They have begun to address cost versus purity trade-off. The preliminary results have not yet been validated, however Japan shared some data with the Working Group to allow participating countries a chance to comment or develop their own data.
The Japanese work was performed based on one selected process: NG on-site SMR-PSA
Product H2 purities: 99 – 99.99%
H2 production capacity: 300 Nm3/h
H2 pressure in the station: 35 MPa

Boundary – charge tank (feedstock reservoir/receiver) to on-board fuel tank
Cost estimation – fixed cost: labor + capital cost + G&A
Variable costs: feedstock, utility, consumables
Operation time – 13 hours/days: affects the facility utilization factor, hence fixed cost portion of supply costs

Preliminary Trade-off results: 

Impurities (ppm)99.99%99%

CO ≤ 1
CO2 ≤ 1
N2 ≤ 50
O2 ≤ 2
HC ≤ 1CO ≤ 100
CO2 ≤ 0.14
N2 ≤ 0.29
O2 ≤ 2
HC ≤ 0.56

PSA recovery80%85%

Efficiency (HHV)73.1%73%

H2 supply cost
(JY/Nm3)110110

Initial preliminary data suggests that in this case:

  • Product hydrogen purity does not affect the hydrogen supply cost significantly, which will not be the driving force to update the threshold limit numbers.
     
  • Fixed cost contribution to total cost is much greater than the variable costs because of the low utilization factor of the facility.
     
  • Attention should be focused more on costs associated with the quality assurance.

This preliminary data has yet to be validated. 

Japan also provided impurity data from the running refuelling stations in Japan. This analysis is made by the station operators – all use reformers – and continuous monitoring of CO at the PSA exit. Batch analysis (varies slightly by station), in general 1-6 times per year of N2, CO, CO2, CH4, O2 at the PSA exit. 

Tests continue. 

No attention to content of inert in Japan currently as almost all NG is imported as LNG – perhaps in the future it will be a mix, but not so significant as in the US. 

Jim Ohi presented the many activities that ASTM has undertaken to address the development of analysis in the Technical Specification. Members of the working group from Japan and Korea agreed to review these draft documents and provide input in support of their use as references for the Draft International Standard. 

Jim Ohi presented the modelling activities undertaken in North America. There was much feedback on specifics of the modelling work to date, including the importance of the variable “R,” which relates to the effects of recirculation.

To the extent possible, WG12 will respond to comments received on TS14687-2 (Document N78) that have not yet been addressed as it prepares the Committee Draft (CD) for an International Standard. Completion of the CD will depend on progress in cell testing, fuel provider integration, and analytical methodology development. Based on data and information needed to prepare the CD and what is received at the next WG12 meeting, a timetable for completion of the CD will be determined at this meeting.

WG12 will conduct its next meeting in conjunction with the ISO TC197 Plenary meeting in Italy in early November.