Temporal grace

Temporal grace was the term used to describe the state in which the interior of TARDISes existed. Supposedly, it ensured no weapons could be used inside the Doctor's TARDIS. (TV: The Hand of Fear) It was linked to the TARDIS' telepathic circuits, and when fully functional, it would negate all hostile and aggressive actions within the ship. (PROSE: The Bodysnatchers) Temporal grace could also stabilise a being affected by time spillage, at least whilst they were within the TARDIS. (AUDIO: Interstitial)

Uses of temporal grace
Temporal grace stopped Eldrad from using her powers. (TV: The Hand of Fear)

While temporal grace was actually switched on, Calvert's energy weapon was unable to fire within the Fourth Doctor's TARDIS. He tested this out, pointed away from the Doctor, as he claimed. (AUDIO: The Evil One)

As part of his con to acquire the Blinovitch Limitation Effect Limiter and give the Fourth Doctor and Romana II the belief he had given the technology to "Sir Charles Kirkland," Drax had equipped a spaceship with temporal grace in order to prevent K9's blaster from working and pushing the Doctor into carrying out his part of the con. (AUDIO: The Trouble with Drax)

Temporal grace prevented Sha'ol from firing his disruptor. (PROSE: Mission: Impractical)

After the Seventh Doctor set off an explosion inside the SARDIT, he commented that the state of grace circuit still needed looking at. (PROSE: Cat's Cradle: Time's Crucible)

When nuclear missiles were launched on an alternate Earth, the Doctor materialised the TARDIS around the whole planet so that the temporal grace would prevent the missiles from exploding. (PROSE: Blood Heat)

Temporal grace, in conjunction with the TARDIS' medical nanites, freed Annie Carpenter from being possessed by the Scourge. (AUDIO: The Shadow of the Scourge)

Temporal grace prevented guns from being used against Nobody No-One, but since he was from another dimension (and as such, operated under different laws of physics), this did not apply to him. (AUDIO: The Word Lord)

Garundel's gun was prevented from working when he planned to shoot Sally Morgan. (AUDIO: Black and White)

The Eighth Doctor repaired the state of grace circuitry. When he drew several Skarasen into the TARDIS, he told his companions that the state of grace within the ship meant that the creatures couldn't harm them. (PROSE: The Bodysnatchers)

The Doctor later admitted to Sam that he had forgotten to reconnect the state of grace circuitry when they were faced with a fusion bomb the Daleks had planted. (PROSE: War of the Daleks)

During the Last Great Time War, temporal grace prevented Gardezza native Osen from shooting in his TARDIS. (AUDIO: Beneath the Viscoid)

According to the Thirteenth Doctor, Dr Leon Perkins' gun was neutralised by the TARDIS the moment he stepped in. (COMIC: A New Beginning)

In another universe, General Sontar tried to kill the Doctor by breaking his neck, but he survived due to the TARDIS' state of grace. Sontar also tried to kill the Rutan ambassador and vice versa in a multitude of different ways but they wouldn't die. (PROSE: The Infinity Doctors)

Failures of temporal grace
According to the Sixth Doctor, temporal grace only worked "while the engines [were] running." (COMIC: Changes)

Nyssa asked the Fifth Doctor about temporal grace not stopping the Cybermen from firing weapons inside the TARDIS, but he only replied, "Nobody's perfect." (TV: Arc of Infinity) Ace also questioned the Doctor about temporal grace after the interior nearly disintegrated. (PROSE: Blood Heat)

The Fourth Doctor revealed that temporal grace was not always switched on. (AUDIO: The Evil One)

After Mels shot the TARDIS console, the Eleventh Doctor admitted that the presence of temporal grace in the TARDIS was (at least, at that point) a "clever lie". (TV: Let's Kill Hitler)

Sontarans, (TV: The Invasion of Time) Cybermen, (TV: Earthshock, Attack of the Cybermen) a Terileptil android, (TV: The Visitation) a Dalek and Jack Harkness (TV: The Parting of the Ways) all discharged their guns in the TARDIS.

Andred's staser did not work, although the Fourth Doctor attributed it to the relative dimensional stabiliser field. However, K9's laser and the Sontarans' guns did work. (TV: The Invasion of Time)

The Eighth Doctor stated that the TARDIS' defence mechanisms sometimes worked and sometimes did not, as he reminded the Monk when Ollistra threatened him with a staser within the TARDIS. (AUDIO: The Side of the Angels)

Threatening the Eighth Doctor with a staser within the TARDIS, Commander Roxita noted that, as a Capitol Guard, he could override the temporal grace. (AUDIO: Day of the Vashta Nerada)