DnD 5e is build around propability rolls (AC, DC) and damage rolls not around bloated stacks of HP that have to be depleted with safe hits. That's the fundamental difference between DnD and DOS2. Adding surfaces sound at first difficult without bloating HP but it really isn't if you adapt the mechanic surfaces work to DnD rules instead of changing everything else to make surfaces work as they are.
My recommendation: Let every character in a surface make a check against an attribute (e.g. constitution) to determine whether he gets the status burn/poisened etc. And than let every character who has such a status make an addional roll every turn to determine whether they take further damage or whether the status ends. There are many mechanics that stun or control that are implemented in exactly that way so why not build surfaces the same way?
