Just saw this post on Imgur and I am not sure about the title. Does that mean that the person has seen something that is really a sore to the eye so he is asking others to call the burn unit to come and rescue him? I couldn't find a better context for this phrase.
One slang meaning of "burn", particularly in American English, is "insult (someone) in a particularly cutting way." This can be used as either a verb or a noun. For example, if Fred insults Jack in a particular witty or brutal fashion, a third party might exclaim "Damn Fred, you really burned him!" (verb) or alternatively "that was a savage burn!" (noun)
In this case, the tweet is calling Selena's music trash (insult), and the author of the imgur caption is describing this insult as a burn, considering it especially sharp or cutting (I'm not sure I would agree, but that is beside the point). The person who has (rhetorically) been burnt here is Selena; the person who burnt her is the twitter poster; the imgur captioner is (humourously, metaphorically) calling the burn unit on Selena's behalf.
The burn(s) unit is a specialist department in a hospital, dealing with (actual!) burns, who would not typically respond to on-site emergencies.