Excellent point, and the difference here is really interesting! Residential refrigerators use a mixture of 90% ammonia and 10% water. This is not very dangerous

Excellent point, and the difference here is really interesting! Residential refrigerators use a mixture of 90% ammonia and 10% water. This is not very dangerous at all, but it also isn't nearly as energy efficient as pure ammonia because it has different thermodynamic properties. Pure ammonia is dangerous because it has an extreme affinity for water and it will dissolve into any water it comes into with. If you breath in ammonia gas, it will dissolve in the mucus of your lungs and draw in more water from the surrounding tissue, flooding your lungs and killing you. If the ammonia is already mixed with a little bit of water, this isn't an issue (hence why you can have ammonia cleaning products in your home). All that said, I was wrong about E-S chillers. I did some more reading and both E-S and absorption chillers use hydrous ammonia.