What are two example of situational irony in Fences?

The ending of the play can be seen as an instance of situational irony.  At Troy's funeral, where all have come to pay their respects, it would be expected that Gabriel would finally be able to sound his horn.  Yet, rather than hearing Gabriel blow his horn in recognition of Troy, the mouthpiece is broken and we see his dance and howl at the reality of what is.  This scene can be seen as situational irony because it represents a combination of expected and real results, the essence of situational irony.  Another instance where there is a collision between what is expected and real results would be where Troy demands to build a fence to keep out death and, in a sense, keep out life.  Yet, the addition of Raynell to the family comes about as a result of death, and, in the process, proves the futility of the desire to want to contain life and stop its progression, regardless of its painful predicament.