All explosive materials must be kept in locked magazines meeting the standards in this subpart unless they are:

1. (a) In the process of manufacture;
2. (b) Being physically handled in the operating process of a licensee or user;
3. (c) Being used; or
4. (d) Being transported to a place of storage or use by a licensee or permittee or by a person who has lawfully acquired explosive materials under § 555.106.