There may not prove to be any legal liability at all. An unfortunate feature of our civil legal system is that plaintiffs can pay legal fees based on a percentage of money recovered, but defendants cannot. Especially for large corporations (like BNSF), it is often both cheaper and better in terms of public relations to simply come to some settlement with a plaintiff, even if there is no legal liability. Plaintiffs’ lawyers are well aware of this, so will often take cases on contingency even if they know there is no real case.
I am not saying that this is true in this particular case, but the fact that lawsuits are filed is not necessarily indicative that there is legal liability.