According to the Aruch Hashulchan (O.Ch. 151 : 5) “ Smoking in Shul is is definitely an
Issur Gamur . There is no greater Kalus Rosh (disrespect).
The only ones who are allowed to smoke (in Shul) are the ones who learn there, all
day or half a day.For them it is like eating food, which is allowed".