Police Officers tasked with guarding the Har Habyis immerse in a mikveh before their shift.

  Today, well over forty percent of the police officers tasked with guarding the Temple Mount immerse in a mikveh before their shift. 

While ascending the Har HaBayit is traditionally prohibited, the rabbis who originally enacted the restriction explained that pikuach nefesh (saving life) overrides it, as the site cannot be left unsecured.

 HaRav Yosef Shalom Elyashiv zt"l ruled that police entry is permissible as long as they immerse beforehand, prompting the construction of an on-site mikveh Medoraysa (built according to biblical stringencies) where officers stand in line during every shift change.

A particularly unique halachic question that arises is the rule on Yom Kippur and Tisha B'Av, given that mikveh immersion is normally not permitted on those days.

 A formal responsum was ultimately issued to permit immersion for this vital duty, which was endorsed by HaRav Avigdor Nebenzahl, Rav of the Churva shul.