What percentage of burns to tbsa will it take to kill you?

There is no exact answer to this question, as there have -- surprisingly -- been cases where 100% of the Total Body Surface Area (TBSA) was in fact burned, and the patient recovered, though if course this is an uncommon result. Burns over 30% BSA are, to my thinking very serious. The reason lies in the way a burn "works". We tend to think of burns as 2-dimensional, but of course they're 3-dimensional. The surface of the burn can dump a lot of the body's water to the outside through evaporation, in cases where the epidermis is interrupted. This is especially dangerous in that, in burns at 30% BSA or more, changes in hematological factors cause edema and restrictions in blood flow in non-burned areas proximal to the actual burn. In the 48 hours post trauma, the severe burn patient suffers from frequently hypovolemia (resultant partially from dehydration through the burned surface), hypoproteinemia, and hemoconcentration (the blood thickens). This syndrome characterically will interfere with proper cardiovascular function throughout the body and, if this process is not interrupted (with hydration -- RL is recommended), Burn Shock is emminent. So the question is not soley percent of burns / TBSA, but also how promptly remediation arrives. If I had to pick a number, I'd say that I start worrying about mortality at 25-30% and become deeply concerned at 60%+, but I need to stress that this is completely dependent on efficacy and promptness of treatment, both at the first-responder and clinical levels.