求翻译：3面积较大、造价昂贵的玻璃，原则上在单位工程交工验收前安装。如确需提前安装则须采取防护措施，在已经施工的玻璃幕墙上覆盖纤维板，防止物体打击损伤玻璃。是什么意思？

3 larger, expensive glass, installed in front of the unit project acceptance in principle. If really necessary to install the protective measures to be taken in advance, have coverage on fibreboard construction of glass curtain wall to prevent glass objects against injury.