Indeed. Household ammonia is only about a 3% solution. No big deal. 30% ammonia can give you a nosebleed if you sniff it. Break a couple bottles of 30% ammonia in a closed room, and people entering that room without an air supply will likely die. TFA doesn't mention the concentration they would use for fuel, but surely the higher the better. I wouldn't want to work on a ship running that stuff. Small leaks of various things are way too common, and ammonia is way too dangerous.