The law if the Sefer Torah fell Chas Veshalom:[1]

In the event that a Sefer Torah ch”v fell on the floor, the custom of the world is to fast. This applies even if it fell with its covering. [This applies even by a Pasul Sefer Torah.[2] This applies even if it fell on its own, such as due to wind, or a child.[3] This applies even if it fell by the steps leading to the Aron Kodesh.[4] This applies even if only one side of the Sefer Torah fell on the floor.[5] This applies even if only the Eitz Hachaim touched the floor.[6] If the congregation is unsure if the Sefer Torah touched the floor, but there is valid testimony of two Kosher witnesses that it did not do so, then no atonement is required.[7] If the person holding the Sefer Torah fell on the floor together with it, then if the Sefer Torah did not touch the floor, no atonement is needed. However, the person who fell is to donate money to charity.[8]]

Who fasts? From the letter of the law, only the person who dropped the Sefer Torah is required to fast.[9] Nonetheless, the custom is for all those who witnessed the fall to fast.[10] Furthermore, some communities are accustomed to decree a fast on all [males] who were present in the Shul and require a Pidyon Taanis [i.e. charity] on all the members of the Shul even if they were not present.[11]

How long is one to fast?[12] There are various customs associated regarding the number of fasts, and when they should take place. Some write that they are to fast for a total of three fasts.[13] The Rebbe once directed in such a case for those who saw the fall to fast for a total of six half days, until midday, and to be careful in saying Shnayim Mikra and giving charity daily throughout that year.[14] Practically, the person who dropped the Sefer Torah is to fast a full day fast, while those who saw it fall are to fast half day fasts.

_______________________________________________________________

[1] Admur 44:2; M”A 44:5 in name of Mishpat Shmuel 12; Kneses Hagedola Y.D. 282; Chaim Sheol 1:12; Shiyurei Bracha Y.D. 282:4 M”B 40:3; See Igros Kodesh 7:83; Shulchan Menachem 3:129; Miasef Lekol Hamachanos 40:4; Piskeiy Teshuvos 40:3; Nitei Gavriel Hachnasas Sefer Torah 29

[2] Chaim Sheol 1:12; Maharsham 2:113; Minchas Elazar 3:52; However, see Urian Telisaiy 91 who is lenient

[3] Afrasakta Deanya 3:194; However, see Yad Yitzchak 2:197 who is lenient

[4] Peri Hasadeh 2:72; Minchas Elazar 3:52

[5] Makor Chaim of Chavos Yair 143; Peri Hasadeh 2:72; Minchas Elazar 3:52; Beis Yitzchak 1:165; Afrasakta Deanya 3:194; Igros Moshe 3:3; See Piskeiy Teshuvos ibid footnote 20

[6] Minchas Elazar ibid

[7] Igros Kodesh 16:244, printed in Shulchan Menachem 3:129

[8] Har Tzevi 1:40

[9] See Shiyurei Bracha Y.D. 282:4 and Chaim Sheol 1:12 that the obligation of fasting only applies to the person who dropped it and not to those who saw it

[10] See Igros Kodesh ibid that those who saw it should fast; Piskeiy Teshuvos ibid

[11] Mentioned in Chaim Sheol ibid; See Piskeiy Teshuvos ibid footnote 26

[12] See Birkeiy Yosef Y.D .282; Piskeiy Teshuvos ibid footnote 26

[13] Orchos Chaim Spinka 40:1

[14] Igros Kodesh ibid