Being roommates has no effect on liability. The issue is whether the other person was at fault. Whether he was at fault will depend on whether he (the roommate) was negligent, or unreasonably careless. If he was negligent--e.g. smoking in bed, using a candle or heater too close to drapes, etc.--he may be liable and your son may be able to sue for medical cost, lost wages, and pain and suffering. If the roommate did nothing wrong--and sometimes accidents happen without it being anyone's fault (for example he happened to trip and fall against table or stove without being careless in tripping), knocking over a candle or hot oil), then there would be no fault and no liability. You son and you should discuss the matter with a personal injury attorney, to see if you have a case and what it might be worth.