Halacha Orach Chaim 189

The fourth Bracha in Birchas Hamazon was instituted to remember those that were killed, and later buried in Baytar. This tragic event concluded the sad end of the second Bais Hamikdosh era. We discussed the history of Baytar by Hilchos Hatov Vhameitiv on wine.

Aruch Hashulchan writes that one of the reasons why we remember this tragedy every time we Bench, is to show how Hashem is looking out for us even in retribution.

After reciting this fourth Bracha, there is a lengthy list of Harachmans and other blessings that were added. Reb Shlomo Zalman Aurbach writes that these additions that follow the words Al Yichasreinu are not imperative to Birchas Hamazon. Someone that is extremely pressed for time can omit them. However, one should keep in mind it is not advisable to exclude these blessings. Regarding someone that is a guest in the home of another person, there is an obligation to bless him, and the blessing for the home owner should not be omitted.

One should answer Amen to all the Harachamons that are recited by others. The blessing does not need to be in the form of a Bracha with the name of Hashem. This includes a Mishuberach after the Torah reading, as well as other Blessings. Shevet Halevi writes that this falls into the category of loving ones friend like oneself. Someone that is learning, and answering will interfere with proper concentration is not obligated to answer to these blessings.