[Retric]

At atmospheric pressure Ammonia liquifies at −28 °F (−33.3 °C), Hydrogen −423.17 °F (−252.87 °C). That alone is a vast improvement. You can build a car/boat/aircraft that keeps its Ammonia fuel tank cool with minimal effort however it’s wildly impractical with hydrogen.

Add the issues with hydrogen embrittlement and Ammonia starts to look trivial by comparison. People deal with industrial quantities of Ammonia on a regular basis without significant issues. Hell even gasoline and diesel are toxic and can be quite dangerous

[aifooh7Keew6xoo]

https://www.nbcchicago.com/news/local/attempt-to-pass-a-tank...

No, they have significant issues on a regular basis still.

[Retric]

Anything dangerous at scale has issues. That doesn’t mean people are unwilling to fill up at a gas station or use other hydrocarbon fuels despite plenty of far worse examples. https://www.npr.org/2021/11/06/1053162519/sierra-leone-oil-t...

And plenty of more recent examples: https://www.fox29.com/news/tanker-truck-fire-closes-stretch-...

Ammonia is one of the most common chemicals manufactured and transported around the world and has plenty of accidents but hydrocarbon accidents get into the hundreds of deaths: 150 dead https://en.wikipedia.org/wiki/Tacoa_disaster 500-600 dead 5000–7000 suffering severe burns https://en.wikipedia.org/wiki/San_Juanico_disaster 167 dead https://en.wikipedia.org/wiki/Piper_Alpha

People even hook up to natural gas lines after events big and small like: 300 dead https://en.wikipedia.org/wiki/New_London_School_explosion or here’s a recent event which destroyed 60-100 homes https://en.wikipedia.org/wiki/Merrimack_Valley_gas_explosion...

[aifooh7Keew6xoo]

My primary point here is that if you see an ammonia spill you're going to die whether or not it explodes.

I suppose it's worth noting in your second link, the fatalities were from the kinetics of the impact, which is a hazard that belongs to "things with velocity" rather than "things containing fuels".

We can assume that uncontained fire and explosion are categorical hazards with fuels.

Ammonia has significant risks that few other proposed fuels present and I believe it's worth considering whether this is something we want moving outside of hazmat routes between industrial zones.

[Retric]

Except the risk of fire / explosion is lower. NFPA 704 for gasoline is 1 Health, 3 fire, 0 Instability where Ammonia is 3 Health, 1 fire, 0 Instability

Major spills of either are dangerous but rare compared to how much is being created and transported. We’re only ~5x as much gasoline vs Ammonia today. Considering most cars would be EV’s I suspect the total amount of Ammonia produced even with widespread adoption isn’t going to change by that much. Say Long haul trucks, heavy equipment, aircraft etc.

PS: Which isn’t to say Ammonia is actually a good fuel, the only thing I can think that actually used the stuff was the X-15. So it would need significant economic advantages to end up adopted.

[ianburrell]

You don’t have to keep it cool. Ammonia has similar profile to propane. It is liquid at 7-14 bar. We build pressure tanks like that all the time for propane.

Ammonia is probably too unsafe for cars and boats. But anything filled by professionals like trains or ships would work. But might work to have tank exchange system like with propane.

[LorenPechtel]

I was thinking about that but it's only a liquid at those pressures if you can keep it from getting too hot--say, a tank sitting there under the desert sun. And if your pressure relief triggers on ammonia it's a lot more of an issue than if it happens with propane.