I don't think Chang lost his arm at the incident , simply because we see him in the pearl orientation film with both arms , and at the end of the movie appears the logo with some copyrights below , and the date, wich is 1980 three years after the incident. And the same happens at the orientation film of the Orchid. My guess is he lost his arm in some kind of a time travel problem , maybe ( if you've seen the complete orientation film of the Orchid ) when the same rabbit Chang is holding appears in the lab , maybe the 2 rabbits looked upon each other and one of them disapeared taking Chang's arm with it. I am not sure about this but i know they were making their best to hide the rabbit from the one that came from the future, so it makes me think there are some big issue if a person/animal who's timetraveling meets his younger/older version, and also a video i saw , chang is talking about time travel and issues, and when he talks about the consequences he skretches and looks at his left arm..
I'm only posting 'cause I've read a lot of people saying that was in the incident that Chang lost his arm ..
feel free to disagree :)