Testing Enclosures : Small Room Retention Times
Some compromises can be made for small rooms (2,500 cu. ft. or less) for two reasons:
- They are not likely to have a large fire that would threaten the rest of the building
- Once trained personnel arrive and open the door, the enclosure integrity (and some of the agent) is lost anyway so shorter retention times can be considered
Select an appropriate retention time
NFPA 2001 states "...the design concentration...shall be maintained for a sufficient period of time to allow effective emergency action by trained personnel".
The following guidelines are suggested for small enclosures.
At a remote site, for example, where re-ignition was possible and where it would take 30 minutes for a responsible party to arrive it should be specified as 30 minutes. On the other hand, a small room with little or no potential for a deep-seated fire and where personnel would respond within 5 minutes would need a retention time of 5 minutes. NFPA 2001 does not recommend any specific time. The authority having jurisdiction must ultimately decide what time is appropriate. ISO does specify 10 minutes.
Each room must have at least one door that will leak about 5 to 20 sq.in. A 350 cu.ft. room with a 14-minute hold time requires a leakage of 7 sq.ft. or less to pass. Since that is not really practical, reducing the specified hold time or an extended discharge is the only option.
Recommended Times for Small Rooms
| For room volumes of: (ft3.) | 2,500 | 1,250 | 625 | 350 |
| (m3) | 70.8 | 35.4 | 17.7 | 9.9 |
| Minimum achievable leakage area is: (sq. in.) | 62 | 42 | 32 | 23 |
| Suggested retention times for inert: (minutes): | 10 | 10 | 8 | 6 |
| Suggested retention times for halocarbons (minutes): | 8 | 6 | 4 | 3 |
