Broadly speaking, the ways in which one may intervene in another's affairs to the latter's advantage are multifarious. Acts of beneficial intervention which may result in quasi contractual obligation, however, fall within the following classes:
(1) The discharge of another's legal obligation.
(2) The preservation of another's life or property.
Under what circumstances may intervention for either of these purposes be said to be a dutiful intervention?
The performance of another's legal obligation may be regarded as dutiful, if it appears:
(a) That the obligation is of such a nature that actual and prompt performance of it is of grave public concern.
(b) That the person upon whom the obligation rests has failed or refused, with knowledge of the facts, to perform it; or that it reasonably appears that it is impossible for him to perform it.
(c) That he who intervenes is under the circumstances an appropriate person.