Chaim Kanievsky | Yisrael Borochov | Yisrael BaAliyah | Yaakov Chaim Sofer | Yisrael Meir Lau | Yisrael Campbell | Yisrael Alter | Yaakov Ben-Tor | Yaakov Yitzchok Ruderman | Yaakov Yitzchak of Lublin | Yaakov Rubinstein | Yaakov Perlow | Yaakov Ne'eman | Shlomo-Yisrael Ben-Meir | Shema Yisrael | Chalav Yisrael | Avraham Yaakov Finkel |
Other authorities allow a firstborn to break his fast under such circumstances (Minchas Yitzchak 9:45; Teshuvos V'hanhagos 1:300, 2:210 in the name of Rabbi Yaakov Yisrael Kanievsky).