That roommate was a separate person. As described in another comment, he tried to set a timer that would not cook anything, only start beeping in thirty minutes. Instead, he set the microwave to run - which is to say, cook - for thirty minutes, which melted the non food item inside the microwave.
A long long time ago, I lived with a roommate who tried to set a timer for thirty minutes on our microwave.
He instead set the microwave to run for thirty minutes.
The steam dome thingy inside did not last for thirty minutes.
Are you that roommate? Or are you saying he tried to set it for 30 seconds?
Neither.
That roommate was a separate person. As described in another comment, he tried to set a timer that would not cook anything, only start beeping in thirty minutes. Instead, he set the microwave to run - which is to say, cook - for thirty minutes, which melted the non food item inside the microwave.
I apologize for the ambiguity of my phrasing.