The highest radiation level detected when approaching the Vault is 3616 rads per second, in the central area: if you get to the door then it will reduce to approximately 2100-3500 rads per second.
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The radiation near the above ground entrance to Vault 87 is the highest in the game (as well as the entire Fallout series), peaking at well over 3,500 rads/second, which is fatal in less than a third of a second.
*The following is based on Fallout 3 cut content and has not been confirmed by canon sources.*
The Overseer's terminal states, "I'm quite sad to report that due to a direct hit from what I presume to be a nuclear weapon on the entry area of Vault 87, we will be unable to provide the Scouting Reports as outlined in Vault-Tec's Operations Manual. The main door to Vault 87 is damaged beyond repair and we are detecting extremely high levels of lethal radiation outside and in the entry tunnel."
*End of information based on Fallout 3 cut content.*
It is possible to reach the entrance through the extensive use of RadAway in combination with clothing providing radiation resistance and Rad-X. However, as the Overseer's message states, the door is inaccessible, making the Vault impossible to enter from above ground. The map marker will activate near the entrance. There is a dead scientist in a radiation suit that can be found near the vault door, as well as RadAway and Rad-X, presumably carried by the scientist, but apparently not enough to prevent her death by massive radiation exposure.
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Ob man das so lösen will, bleibt natürlich jedem selbst überlassen.
