An obligor is not liable for his failure to perform when it is caused by a fortuitous event that makes performance impossible.
An obligor is, however, liable for his failure to perform when he has assumed the risk of such a fortuitous event.
An obligor is liable also when the fortuitous event occurred after he has been put in default.
An obligor is likewise liable when the fortuitous event that caused his failure to perform has been preceded by his fault, without which the failure would not have occurred.
La. C.C. § 1873