Safety Assessments of Ammonia as a Transportation Fuel

New data from a number of ammonia energy safety studies will be published later this year. In the meantime, two excellent reports already exist that provide comparative, quantitative risk analyses. Each compares the risks of using ammonia as a fuel in passenger vehicles against the risks of other fuels, including gasoline, LPG, CNG, methanol, and hydrogen. Both conclude that the risks associated with using ammonia as a fuel are “similar, if not lower than for the other fuels.”

The first report, written by Risø National Laboratory in Denmark, examines the risks of using ammonia as a fuel for internal combustion engines and also for fuel cells, and was commissioned as part of the EU-supported project “Ammonia Cracking for Clean Electric Power Technology” in 2005. The second, written by Quest Consultants Inc, was prepared for Iowa State University in 2009 and examined three areas of fuel risk: “bulk movement, storage, and dispensing … The objective of the study was to compute the level of risk posed to the public near an average roadway along which the fuels would be transported in road tankers, and near an automotive fueling station.”

Conclusions: ammonia risk levels are acceptable and similar to current fuels

The Quest report:

Click to download report

In summary, the hazards and risks associated with the truck transport, storage, and dispensing of refrigerated anhydrous ammonia are similar to those of gasoline and LPG …The risks associated with all three fuels would fall into the acceptable category for all referenced risk criteria.

Quest Consultants Inc, Comparative Quantitative Risk Analysis of Motor Gasoline, LPG, and Anhydrous Ammonia as an Automotive Fuel (USA, 2009)

The Risø report:

Click to download report

An overall conclusion is that the hazards in relation to ammonia need to be (and probably can be) controlled by technical and regulatory options …When these safety systems are implemented, the risks of using ammonia is similar, if not lower than for the other fuels.

Risø National Laboratory, Safety assessment of ammonia as a transport fuel (Denmark, 2005)

Ammonia fuel risk is “acceptable” … What does that mean?
The first and most important conclusion we can draw from these studies is that, based on the data, safety should not be an obstacle to the funding, development, or demonstration of ammonia energy projects. As we move from technology development to real-world demonstration installations, site-specific safety analyses will be essential – and data from these will begin to be published later this year – but, immediately, we can examine the existing literature and be confident that the risk levels of ammonia can be adequately managed.

It is important to note, moreover, that this “acceptable” risk profile was achieved in perhaps the highest possible risk scenario: passenger cars in public places. It is likely that initial market adoption of ammonia as an energy vector will take place in remote settings and professionalized sectors where safety and training can be tightly controlled, for example, stationary power generation, or maritime fuel, or economical bulk transport and safe storage and distribution of renewable hydrogen.

Unlike most other proposed alternative fuels, ammonia is already one of the most produced chemicals on the planet, with global production of 180 million tons per year, and international trade and regional distribution of tens of millions of tons per year. This level of activity comes with a 100-year accumulation of safety experience, including know-how for keeping employees and customers safe, a mature international set of laws and regulations, and a sophisticated support sector providing ammonia users and first responders with safety equipment, training, and education. In the words of Norm Olson, former President of the NH3 Fuel Association, almost all the issues surrounding ammonia fuel safety are “engineering problems with engineering solutions.”

The Quest report goes into detail on fuel distribution (truck transport) and service stations, and it describes both the quantitative risks and the engineering solutions available to mitigate those risks.

Truck Transport Safety

Figure 6-2: Vulnerability Corridors and Zones for the Truck Transport of Gasoline, LPG, and Refrigerated Ammonia. Click to enlarge. Quest Consultants Inc, Comparative Quantitative Risk Analysis of Motor Gasoline, LPG, and Anhydrous Ammonia as an Automotive Fuel (USA, 2009)

In its review of truck transport safety, which assesses the risks to the public posed by the supply chain distributing fuel from centralized storage to local fueling stations, the Quest report begins with a simple count of the frequency of “releases” per mile in the existing fleet of gasoline, LPG, and ammonia transport trucks.

Today, ammonia has the lowest probability of an accidental release in truck transport.

  • Gasoline: 1.75 x 10-7 releases/mile/truck
  • LPG: 5.84 x 10-8 releases/mile/truck
  • Ammonia: 1.9 x 10-8 releases/mile/truck
Figure 14: Individual risk of different technological solutions for the transportation of ammonia by road tankers. Click to enlarge. Risø National Laboratory, Safety assessment of ammonia as a transport fuel (Denmark, 2005)

“Nevertheless, risk-reducing options are strongly needed,” and the Risø report illustrates not only how to further decrease the probability of a release but also how to reduce the impact of any such release:

“A solution that causes the risk levels to drop below the risks for LPG requires that ammonia be transported in refrigerated form, in road tankers carrying typically four separated (pressure) tanks of about 11 m3 each, which are as resilient against impact and abrasion as conventional (large) pressure tanks.”

Service Stations

Figure 6-4: Risk Contours for a Service Station Storing and Dispensing Gasoline. Click to enlarge.
Figure 6-6: Risk Contours for a Service Station Storing and Dispensing Anhydrous Ammonia. Click to enlarge.
Figure 6-5: Risk Contours for a Service Station Storing and Dispensing LPG. Click to enlarge. Quest Consultants Inc, Comparative Quantitative Risk Analysis of Motor Gasoline, LPG, and Anhydrous Ammonia as an Automotive Fuel (USA, 2009)

The Quest report provides visualizations of its analysis of the hazards of storing and distributing fuels at a service station located on a road intersection in a populated area.

These “Risk Contours” for Gasoline, LPG, and Ammonia are useful tools for communicating the relative risks of ammonia (colored red) versus gasoline (colored orange) because, at first glance, it is clear that the risk levels of ammonia and gasoline are similar. By contrast, the risk levels for LPG (colored green) are clearly greater.

We already know and accept the risks of distributing gasoline at fuel stations. We also know and accept the risks for LPG in those areas where LPG is utilized as a fuel. Therefore, if we were rational and based our decisions on data, there should be no doubt that we would also accept the risks of distributing ammonia at fuel stations.

And again, I should stress that neither report suggests that we simply accept these risks, because the engineering problems with handling ammonia safely have engineering solutions.

One simple engineering solution is to build a buffer zone around fueling stations:

Small, but long-lasting releases of ammonia due to e.g. leaks and ruptures of hoses, cause serious dangers at distances up to 150 m distance …

This requires additional technical safeguards to reduce the likelihood of these releases (It is especially important to stop the release as soon as possible to interrupt exposure). But also in case these safeguards are in place, safety distances around these ammonia-refuelling stations should be no less than 70 m.
Risø National Laboratory, Safety assessment of ammonia as a transport fuel (Denmark, 2005), pp39-40

A more sophisticated solution, which goes further toward eliminating risks, would be to use underground, refrigerated, double-walled storage tanks:

The refrigerated ammonia storage system is designed such that if a small or significant release of ammonia were to occur in the storage, heating, or pumping systems, the released ammonia liquid and vapor would be contained in a vault and vented through a vertical stack extending upward. As the ammonia vapors warm and disperse from the elevated stack, the ammonia/air plume will be positively buoyant and will have no ability to slump back to grade. This storage method essentially eliminates the grade-level risk associated with the storage of refrigerated ammonia.
Quest Consultants Inc, Comparative Quantitative Risk Analysis of Motor Gasoline, LPG, and Anhydrous Ammonia as an Automotive Fuel (USA, 2009), p50 (section 6-10)

Driving a Car
It might be an uncomfortable fact when contemplating fuel safety, but our future fuel choice will probably not be the greatest risk on the road. Speed and human error are far more dangerous.

The fuel used to power a motor vehicle does not contribute significantly to the fatality rate of motor-vehicle accidents …

This conclusion is based on a simple review of the available NSC data and would be expected to be true if anhydrous ammonia were the automotive fuel since anhydrous ammonia would be carried in a
pressure vessel similar to LPG.
Quest Consultants Inc, Comparative Quantitative Risk Analysis of Motor Gasoline, LPG, and Anhydrous Ammonia as an Automotive Fuel (USA, 2009), pp9-10 (sections 1-3, 1-4)

Click to enlarge. Risø National Laboratory, Safety assessment of ammonia as a transport fuel (Denmark, 2005)

Nonetheless, the Risø report describes the engineering solutions to the engineering problems and provides specifications for an onboard fueling system that includes additional safety systems.

For example, the fuel tank itself (“consisting of carbon fibres with a inner lining of polyethylene”) is designed so that the “advantage over steel tanks is that it excludes (which has been proven for LPG) explosive failure of the tank in a fire.”

Ammonia Fuel Risk Levels: “Similar, if not Lower than” Gasoline, LPG, Methanol, Natural Gas, and Hydrogen
The main point here, beyond providing links to the two reports for those who wish to read further, is to demonstrate that ammonia safety should not be a barrier to the development and demonstration of ammonia fuel technologies.

This post is based on a presentation I gave at Argonne National Laboratory, on September 22, 2015, at the twelfth annual NH3 Fuel Conference: Ammonia Fuel Risk Levels: “Similar, if not Lower than” Gasoline, LPG, Methanol, Natural Gas, and Hydrogen. On the same morning that I delivered the presentation, the news broke that Volkswagen had admitted wrongdoing in the defeat device emissions scandal, which became known as Dieselgate. I quoted the statement of Michael Horn, President and CEO of the Volkswagen Group of America: “Let’s be clear about this, our company was dishonest – with the EPA, and the California Air Resources Board, and with all of you. And, in my German words, we have totally screwed up.”

The point I made that day, which stands even more strongly today following the growing bans of gasoline and diesel cars – outlawed in Norway from 2025, in Scotland and Sweden from 2032, across the whole UK and France from 2040 – is that in our consideration of future fuel safety we should be comparing the manageable risks of ammonia, which are immediate and internalized in the fuel risk profile, against the unmanageable risks of refined fossil fuel combustion, which are long-term and externalities, causing health impacts far from the point of use.

Ammonia is a hazardous chemical and it must be treated with respect, and also it can be an excellent fuel. As the Risø report concludes, “the acceptance of ammonia will not be based on the results of numerical risk analysis, but will also be influenced by the public’s perception of the threats of ammonia.”


  1. John Hopmans says:

    I worked for 35 years in Chemical Industry and Oil Refining and I agree that NH3 is not more dangerous than the present fuels and any requirement can be accommodated by proper engineering. Fish toxicity is an issue and might require additional bund walls near rivers or sea.

    However I can not see ammonia to become a fuel for road transport.The power to wheel efficiency is 35% at best. Compare that to 85% power to wheel efficiency for batteries. Besides clean ammonia is very expensive to produce for now, because of the high investment cost of electrolysers.

    I can see it being used for marine fuel and peaker fuel but not for road transport

  2. Joe Beach says:

    I’m not sure that power to wheel efficiency is the right metric for road transport. I think it is $/mile or $/year, plus the cost of required infrastructure changes and the more intangible aspects of year-round vehicle performance (cold batteries don’t work well) and vehicle range. The analyses I have seen only show electric passenger vehicles being preferable for applications in which the vehicle is driven 100-200 miles per day consistently, like in taxis. Basically, near the range limit for the vehicle. In shorter range uses (typical American commuter) ICE vehicles have a lower total cost of ownership. In long range applications (long distance trucking), electric vehicles don’t have adequate range and would require huge electrical infrastructure changes to allow for frequent charging.

    A clean chemical fuel like NH3 has a big infrastructure advantage because it can be stored for months and transported to fueling stations just like gasoline and diesel are. Months-long storage allows it to be synthesized when wind and solar resources are most available and then used whenever it is needed. Distribution by truck means we don’t have to spend a huge amount of time and money upgrading transmission and distribution lines. By comparison, large scale use of battery electric vehicles requires that electricity is available whenever the vehicle needs to be charged, which means lots of expensive transmission and distribution line upgrades and overbuilding of wind and solar resources so adequate charging power is available even in low-production times of the year.

    • John Hopmans says:

      Yes Joe, I agree that both EV and HFV require an overhaul of the infrastructure. But I believe that the infrastructure change to hydrogen is much more far-reaching than for batteries, assuming a density of distribution points like now for gasoline.

      And you are right we should translate efficiency and investment cost into money/mile or money/MWh on the wheels. But that is easy using Lazard’s method. If we assume off-shore wind as source (@70$/MWh) and that the cost of an EV is equal to that of a HFV(?) then we only have to compare the process cost from source to wheels. If we further assume an investment cost of 315$/kW (ref IEA report “ Renewable Energy for Industry”) for 100% efficient electrolysis and an electrolysis efficiency of 60% then the cost of power via hydrogen is $280/MWh and via battery is 85$/MWh.

      Therefore I suggest to aim for batteries in road transport and use ammonia for marine, aviation(??) seasonal backup using H2-GTCC and also H2-GTCC peakers. I know that this far away in the future.

      By the way I live in Europe and the cost of ownership of EV is now equal to ICE (high gasoline prices). People are hesitant to make the jump because of lack of (super)chargers and lack of range. Once that is solved, it is expected that it takes off big.

  3. Mikel Syn says:

    With cars, maybe. Long haul trucks and trains that serve the rural parts of the country though, battery/direct electric transmission is not viable. These will need an intermediate storage medium such as compressed H2 or in this context, ammonia.

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