From N.F.P.A. Pamphlet 2001, Standard on Clean Agent Fire Extinguishing Systems, 2000 Edition:

4-4 Enclosure Inspection.
At least every 12 months, the enclosure protected by the clean agent shall be thoroughly inspected to determine if penetrations or other changes have occurred that could adversely affect agent leakage or change volume of hazard or both. Where the inspection indicates conditions that could result in inability to maintain the clean agent concentration, they shall be corrected. If uncertainty still exists, the enclosures shall be retested for integrity in accordance with 4-7.2.3. Exception: An enclosure inspection is not required every 12 months if a documented administrative control program exists that addresses barrier integrity.

4-7.2.3* Review Enclosure Integrity.
All total flooding systems shall have the enclosure examined and tested to locate and then effectively seal any significant air leaks that could result in a failure of the enclosure to hold the specified agent concentration level for the specified holding period. The currently preferred method is using a blower door fan unit and smoke pencil. Quantitative results shall be obtained and recorded to indicate that the specified agent concentration for the specified duration of protection is in compliance with Section 3-6, using an approved blower fan unit or other means as approved by the authority having jurisdiction. (For guidance, see Appendix B.)