Shall be allowed only in the following instances: (a) In cases of two failed biddings, as provided in Section 35 hereof; (b) In case of imminent danger to life or property during a state of calamity, or when time is of the essence arising from natural or man-made calamities or other causes where immediate action is necessary to prevent damage to or loss of life or property, or to restore vital public services, infrastructure facilities and other public utilities; (c) Take-over of contracts, which have been rescinded or terminated for causes provided for in the contract and existing laws, where immediate action is necessary to prevent damage to or loss of life or property, or to restore vital public services, infrastructure facilities and other public utilities; (d) Where the subject contract is adjacent or contiguous to an on-going infrastructure project, as defined in the IRR: Provided, however, That the original contract is the result of a Competitive Bidding; the subject contract to be negotiated has similar or related scopes of work; it is within the contracting capacity of the contractor; the contractor uses the same prices or lower unit prices as in the original contract less mobilization cost; the amount involved does not exceed the amount of the ongoing project; and, the contractor has no negative slippage: Provided, further, That negotiations for the procurement are commenced before the expiry of the original contract. Whenever applicable, this principle shall also govern consultancy contracts, where the consultants have unique experience and expertise to deliver the required service; or, (e) Subject to the guidelines specified in the IRR, purchases of Goods from another agency of the Government, such as the Procurement Service of the DBM, which is tasked with a centralized procurement of commonly used Goods for the government in accordance with Letters of Instruction No. 755 and Executive Order No. 359, series of 1989