The Gates of Hell

"The unbelievers will be led to Hell in crowds until, when they arrive there, its gates will be opened.."
[az-Zumar, 39: 71]

"And verily, Hell is the promised abode for them all. It has seven gates: to each of those gates is a specific class of sinners assigned."
[al Hijr, 15: 43-44]

"To them will be said, 'Enter you the gates of Hell to dwell therein. And how evil is this abode of the arrogant.'"
[az Zumar, 39: 72]

"But those who reject Our signs are the companions of the left hand - on them will be fire vaulted over."
[al Balad, 90: 19-20]

In Arabic, the phrase "on them will be fire vaulted over" indicates that the gates of Hell be closed. In other words, the fire will encompass the companions of the Fire, and the gates of Hell will imprison them within. As well, the gates of Hell will be locked, vaulted all around, and outstretched columns will cover the doors.

"It is the fire of Allah, kindled to a blaze, which mounts right to the hearts. It will be a vault over them in outstretched columns."
[al Humazah, 104: 6-9]

Abu Hurairah (radiAllahu anhu) narrated that Allah's Messenger (salAllahu alayhi wasalam) said: 'When the month of Ramadan begins and the gates of Heaven are opened, the gates of Hell are closed, and the devils are chained."
[Sahih al-Bukhari]