The Board shall not be responsible for loss of or damage to goods, while in their custody, by fire, water used in extinguishing fire, or vermin, nor for loss or damage to ironwork or such character of goods in an unprotected state which may be stacked on the wharves or jetties or any land under the jurisdiction of the Board, and any action of the members in endeavouring to temporarily cover or protect such goods shall not be held to cast upon them any liability for loss or damage as aforesaid.