If you believe in the Three-Act structure, then the first disaster corresponds to the end of Act 1. The second disaster is the mid-point of Act 2. The third disaster is the end of Act 2, and forces Act 3 which wraps things up. It is OK to have the first disaster be caused by external circumstances, but I think that the second and third disasters should be caused by the protagonist’s attempts to “fix things”. Things just get worse and worse.