Kelim, Chapter One, Mishnah Nine
1) The area between the porch (ulam) and the altar is holier, for [priests] who have blemishes or unkempt hair may not enter it.
2) The Hekhal is holier, for no one whose hands or feet are unwashed may enter it.
3) The Holy of Holies is holier, for only the high priest, on Yom Kippur, at the time of the service, may enter it.
4) Rabbi Yose said: in five respects the area between the porch and the altar is equal to the Hekhal,
i) for those afflicted with blemishes
ii) or with a wild growth of hair,
iii) or who have drunk wine
iv) or whose hands or feet are unwashed may not enter there,
v) and the people must keep away from the area between the porch and the altar when the incense is being burned.
Section one: There were 22 cubits between the porch and the altar (see Middot 3:6, 5:1). This section is off-limits to a priest who is blemished (Leviticus 21:17), or one who grew his hair too long (Leviticus 10:6).
Section two: Priests who had not washed their hands and feet could not enter the Hekhal, the Sanctuary. However, according to the first opinion they could enter the area between the porch and the altar without washing their hands.
Section three: The highest degree of sanctity is accorded to the Holy of Holies, for the high priest could only enter there once a year, on Yom Kippur.
Section four: According to Rabbi Yose the prohibitions that the first opinion says begin at the Sanctuary, begin between the porch and the altar. He also holds that priests who had drunk wine (or other alcohol) cannot go into this area (see Leviticus 10:9). If you go back and count, Rabbi Yose holds that there are ten levels of holiness whereas the first opinion holds that there are eleven.
In addition, when the incense is being burned on a daily basis, the people must leave both the Sanctuary and the area between the porch and the altar. On Yom Kippur they need not withdraw all the way to the porch, but rather just leave the Sanctuary itself.