withdrawal envelope是什么意思

The escape route, personnel access route, maintenance route and withdrawal envelope models shall be updated as the design progresses and used in the clash checking of the models.
请教大家这里withdrawal envelope是什么意思？
这段句子的上面还有另外一句

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Maintenance withdrawal envelopes for removal of equipment internals

逃逸通道，访问通道，维护通道和抽出空间模型应随设计进展升级，并用于碰撞检查。
维护抽出空间用于设备内件抽出。