An employer who engaged in operations specified in section 13(b)(4) which he performs on the marine products and byproducts described in that section may operate a business which engages also in operations of a different character or one in which some of the activities carried on are not functionally necessary to the conduct of operations named in section 13(b)(4). In such a business there will ordinarily be, in addition to the employees employed in such named operations, other employees who are nonexempt because their work is concerned entirely or in substantial part with carrying on activities which constitute neither the actual engagement in the named operations nor the performance of functions which are, as a practical matter, directly and necessarily a part of their employer's conduct of such named operations. Ordinarily, as indicated in § 784.156, such nonexempt employees will not be employed in an establishment which is exclusively devoted by the employer to the named operations during the period of their employment. It is usually when the named operations are not being carried on, or in places wholly or partly devoted to other operations, that employees of such an employer will be performing functions which are not so necessarily related to the conduct of the operations named in section 13(b)(4) as to come within the exemption. Typical illustrations of the occupations in which such nonexempt workers may be found (although employment in such an occupation does not necessarily mean that the worker is nonexempt) are the following: General office work (such as maintaining employment, social security, payroll and other records, handling general correspondence, etc., as distinguished from “marketing” or “distributing” work like that described in § 784.155), custodial, maintenance, watching, and guarding occupations; furnishing food, lodging, transportation, or nursing services to workers; and laboratory occupations such as those concerned with development of new products. Such workers are, of course, not physically engaged in operations named in section 13(b)(4) in the ordinary case, and they are not exempt unless they can be shown to be “employed in” such operations on other grounds. But any of them may come within the exemption in a situation where the employer can show that the functions which they perform, in view of all the facts and circumstances under which the named operations are carried on, are actually so integrated with or essential to the conduct of the named operations as to be, in practical effect directly and necessarily a part of the operations for which exemption was intended. Thus, for example, if canning operations described in section 13(b)(4) are carried on in a location where the canning employees cannot obtain necessary food unless the canner provides it, his employment of culinary employees to provide such food is functionally so necessary to the conduct of the canning operations that their work is, as a practical matter, a part of such operations, and the exemption will apply to them. On like principle, the exemption may apply to a watchman whose services are required during performance of the named operations in order to guard against spontaneous combustion of the products of such operations and other occurrences which may jeopardize the conduct of the operations.