Article 79(1) remains the controlling provision even if a contracting party has engaged a third person to perform the contract in whole or in part.
(a) In general, the seller is not exempted under Article 79(1) when those within its sphere of risk fail to perform; for example, the seller's own staff or personnel and those engaged to provide the seller with raw materials or semi-manufactured goods. The same principle applies to the buyer in relation to the buyer's own staff or personnel and those engaged to perform the obligations of the buyer under the contract.
(b) In exceptional circumstances, a contracting party may be exempted under Article 79(1) for the acts or omissions of a third person when the contracting party was not able to choose or control the third person.