Todah

There is a discussion in the Achronim if there is an obligation on the 4 people that have been saved to bring a korban todah or if it is a nedavah.  Rashi on Chumash, Menachot (79b) and Tosfos Rid Rosh Hashana (5b)5 seem to hold that it is a chiuv.  However, the Shittah in Menachot disagrees with Rashi as does the Tur on Chumash.  There are a lot of other mekorot, see some of the discussion on the otzar forum.  

The Panim Yafos says the reason the Torah did not mention the chometz loaves of the todah in parshat Vayikra as an exception to the rule of normally not allowing chametz in the Mishkan is because the todah is not an obligation.  The Chatam Sofer says the todah is recorded in Tzav and not Vayikra because Tzav is the commandments to the kohanim, the tzaddikim, and they bring a todah even when there is no obligation because of the נסיך שבכל יום and hence the Torah says אם על תודה, a reshus, for we are talking about the voluntary todah. 

R.A.E. siman 119 cites the sefer Orim Gedolim has a safek if one person is saying hagomel for one version of being saved can he be motzei someone else who has to say it for a different reason, ואם המברך חייב ומברך הברכה על שהיה חולה ונתרפא וזה שומע חייב בברכה על שהיה הולך מדבר מסתפק בס' אורים גדולים בדרשותיו פ' צו די"ל דיוצא בלא עניית אמן או דאף בעניית אמן אינו יוצא עיי"ש.  The question seems to be if there is a general name of korban todah for all those that need ot bring a todah or the reason for the bringing becomes part of the name of the korban. Rav Yitzchak Sorotskin cites at least a הו"א to this idea that the reason for the obliation becomes part of the name of the korban from Rashi Zevachim (7a) that explains the chiddush the Gemarah says that if one shects a todah for the sake of another todah that one is obligated that it is valid for אע"פ שלא באו על הודייה אחת דארבעה צריכין להודות כדאמרינן בברכות (דף נד:) וכתיב בהו (תהילים ק״ז:כ״ב) ויזבחו זבחי תודה ושחט תודה בשעת עלייתו מן הים לשם תודה שהפריש על יציאתו מבית האסורין.