Rubrics
There are rules regarding who may enter or leave the sanctuary (altar), and by which door. Neither the Beautiful Gates (Holy/Tsar doors - central doors)) nor the space between them and the altar table may be used by laity under any circumstances, although infants are either carried into the altar through them in the "churching" rite if they are boys, or if they are girls, the infant is simply presented at the doors. Bishops may enter through the Beautiful Gates at any time; priests and deacons may do so only at specific times during the services when the Gates are open (but during Bright Week they always enter and exit through them). All others enter the sanctuary through the side doors.
In a convent only the abbess and elder nuns are permitted to enter the sanctuary(altar), and only by the side doors. The abbess may enter at any time, but the other nuns need a blessing to enter.
Male members of the laity who are usually allowed to enter the sanctuary include those involved in the running of the particular church, i.e. cantors and choristers, altar servers/acolytes, church keepers and vestrymen, etc. Entering the sanctuary for no good reason or without a blessing is forbidden even if no religious service is being held at the time.
In the Romanian tradition, on the day of the consecration of the altar in the church, the laity, including women, are permitted to enter and venerate the altar up until the beginning of the Vespers of Consecration.
These guidelines were developed over the course of many centuries, with both theologically symbolic and practical reasons for them.
Read more about this topic: Iconostasis