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Switched rooms or talked between the blessing and the Mitzvah: 
One who said a blessing and switched areas prior to wearing the Tallis, then if he went from inside the house to outside the door of the house, he must repeat the blessing, even if he did not speak at all in-between. [The same applies vice-versa, if he was outside the house and he went from outside to inside.] If however he did not leave from inside to outside the house in-between, and simply went to a different room within the same house, then the blessing is not required to be repeated, so long as he did not speak in-between of unrelated matters or make another form of invalidating interval [and had in mind to switch rooms upon reciting the blessing].
If after saying the blessing one realized his Tallis is Pasul, or his Tallis was taken, what is he to do?
If after reciting the blessing, prior to wearing the Tallis, one realized his Tallis is Pasul or was taken away, then if he does not have another Kosher Tallis readily available, he is to say Baruch Sheim Kevod Malchuso Leolam Vaed. If however another Kosher Tallis is available, then if he had it in mind at the time of the blessing over the Pasul Tallis, he is to wear the second Tallis on the basis of this blessing, and hence save the blessing from being in vain. If however he did not have in mind to wear the second Tallis at the time of the blessing [which is usually the case] then some Poskim rule a new blessing is to be recited [and he is to say Baruch Shem] while other Poskim rule a blessing is not to be repeated.
Can one immediately tie new Tzitzis to the Tallis and then wear it on the basis of the blessing? If after reciting the blessing, prior to wearing the Tallis, one realized his Tallis is Pasul and he has Kosher Tzitzis strings available in the area that he is in, then if he immediately replaces the invalid Tzitzis and avoids any interval, he can wear the Tallis on the basis of his past blessing, and thus save the blessing from being in vain.
If one said a blessing on a Tallis and before wearing it he realized that the Tallis is not his, can he put on his Tallis instead?
No. He is to put on the mistaken Tallis and wear it for a few moments, and he may then switch and wear his Tallis with a new blessing.
 Admur ibid; Michaber 8/13
The reason: As this change of area is considered an interval between the blessing said over the first Tallis, and the wearing of the second Tallis and he must thus repeat the blessing. [ibid] It is not the walk and delay that is considered an interval but the actual change of area. [Admur ibid in Kuntrus Achron 5]
Other opinions: Some Poskim rule that changing areas is never considered an interval, even if he went from inside to outside, unless he talked in-between. [Bach 8; Olas Tamid 8/17; Taz 8/11; Zera Emes 1/2; Chayeh Adam 12/5; M”B 8/34; Kaf Hachaim 8/50; Piskeiy Teshuvos 8/23-6 and 8/26 that so is the practical custom] The Poskim negate this opinion. [Michaber 8/13; M”A 8/17; Admur ibid] In Kuntrus Achron 8/5 Admur answers all the questions of the Taz and concludes “After answering all the questions of the Taz, certainly we rule like the Shulchan Aruch.”
The law if one can see original area: Regarding Birchas Hanehnin [178/1; Seder 9/11] and Kiddush [273/2] Admur rules that if one sees the original area from his new area then it is not considered an interval. Seemingly, the same law applies regarding Birchas Hamitzvos, that if one can see the original area it is not considered an interval. Vetzaruch Iyun, as no mention of this has been made either here in 8/22 or in 432/8 regarding Bedikas Chameitz.
 Having in mind to switch rooms at the time of the blessing: Seemingly, it is required for him to also have in mind to switch rooms at the time of the original blessing. See 178/1; Seder 9/11 [regarding Birchas Hanehnin]; 273/2 [regarding Kiddush] that one must have in mind at the time of the original blessing, otherwise it is considered a Hefsek. On the other hand, no mention of this is made in 8/22 or 432/8. However, one can assume that in both Halachas it refers to a case that one had in mind, as in 8/22 he knew the Tallis was in another room, and in 432/8 he knew he must check the entire house. Vetzaruch Iyun!
 Admur ibid; M”A 8/19
The reason: As since the two rooms are within the same house it is not considered an interval for him to go from one room to another. [ibid]
Other opinions: Some Poskim rule a blessing is not to be said even if an interval was made in-between. [2nd opinion in Michaber Y.D. 19/5; Final ruling of Taz Y.D. 19/9; Final arbitration of P”M 8 A”A 14; Shaareiy Teshuvah 8/12; Zivcheiy Tzedek 1/19-24; Kaf Hachaim 8/45; In M”A 8/14 there is question as to the correct version of his statement, Admur in KU”A ibid states the correct Nussach is that he has to say the blessing]
 M”B 8/30
 P”M 8 M”Z 14; Ashel Avraham Butchach; Artzos Hachaim 8/13; Toras Chaim Sofer 8/16; Yabia Omer 3 Yoreh Deah 17; Vayeishev Moshe 1/86; Piskeiy Teshuvos 8/24; The following Poskim rule this way regarding Shofar: M”B 585/4; Binyan Olam 31 brought in Piskeiy Teshuvah and Kaf Hachaim 585/15; Shaar Hatziyon 651/74 regarding Daled Minim
The reason: As it is similar to a fruit that became destroyed after one said the blessing in which case we rule that another blessing must be recited. [See Michaber 206/6]
 Mutzal Meish 14 [Safek Brachos Lihakel]; Shaareiy Teshuvah 8/16; Chesed Lealafim 8/10; Tehila Ledavid 8/9; Daas Torah 8; Sefer Hachaim 8 [of Rav Shlomo Kluger]; Poskim in Kaf Hachaim 8/55 [and so is his opinion]; Betzeil Hachachmah 6/16; The following Poskim rule this way regarding Shofar: Kaf Hachaim 585/15 and 37; Maharshag 1/57; Kinyan Torah 7/44; Piskeiy Teshuvos 585/6
The reason: As it is not similar to a blessing over food, being that by food the blessing only goes on the specific food one has in his hand. However by a Mitzvah the blessing covers any item that can be used for the Mitzvah. [Poskim ibid]
 M”B 8/41 in name of Artzos Hachaim; Biur Halacha 25/12 “Mihadek”
 Based on previous Q&A that when one does not have the second Tallis in mind it is disputed whether a new blessing is to be recited, and hence in order to avoid this dispute, one should wear the original Tallis and only then wear his Tallis without a blessing.