I had a terrible experience this Friday. I was motivated to clean the oven. I think through lifehacker I read a sustainable method which included ammoniac and boiling water. It is simply placing a boiling water in a pot in the oven and adding a cup of ammoniac in a shelf above the pot and leaving it overnight. Well, there was a terrible smell of ammoniac already in 5-10 minutes so I had a panic attack. Poured the ammoniac to the sink and opened the windows. I realised that this was a dangerous thing to do. I did not inhale but smell ammoniac. I took a mid-night walk, stayed in the balcony and in the bedroom, which even had smell.
Here is another method, rather a safe one. Throw the oven