Room Integrity Testing
Due to the overall characteristics of FM-200 the sealing requirements for effective retention are much more stringent than those for any of the Inert agents.
In general an enclosure protected with FM-200 needs to be sealed to reduce the leakage by at least half that allowed for the Inert Agents, this can and does have an impact on the structural sealing costs. If an enclosure has satisfied an Integrity Test utilising Halon as the medium it will definitely satisfy the requirements for any of the inert agents resulting in no additional structural costs. Unless the result with Halon is in excess of 12.5 minutes it will not satisfy the requirements for containing FM-200 resulting in the need for structural improvements inevitably leading to an increase in building costs.
Fire Stopping/Enclosure Sealing
The Integrity of an enclosure is defined as the ability of the structure to adequately retain an extinguishing agent at a suitable level of concentration to suppress a fire condition. For any Gaseous Fire Suppression Installation to be effective, the design concentration must first be achieved, and then maintained at suitable levels within the risk, to achieve this the enclosure must be adequately sealed. This is verified by performing an enclosure integrity test upon completion of the installation, by carrying out the Integrity Test at the same time as the sealing works it is possible to obtain a positive result.
It is the responsibility of the user and system suppliers to ensure that the enclosure and extinguishing system meet the design requirements. At contract stage it is essential that responsibility for each of the enclosure requirements is made clear to all concerned.
The term enclosure refers to the solid boundaries (walls, floor and ceiling) forming the room or compartment that contains the asset(s) to be protected by the extinguishing system. In a normal room the floor void and ceiling space are generally considered as part of the same enclosure, with the boundaries formed at the floor slabs and partitioning in the suspended floor and ceiling. There are four critical design factors to consider for each protected enclosure:
Enclosure strength (to withstand pressure during discharge)
Enclosure fire resistance/Precautions (to withstand fire external to the enclosure)
Enclosure pressure relief (to constrain the pressure differential across the enclosure structure to an acceptable level, by venting off excess enclosure gases during agent discharge)
Enclosure integrity (to aid retention of the agent after agent discharge);
The primary purpose in defining the boundaries of an enclosure is to define the volume that is to hold the agent. Unexpected or excessive loss of agent from an enclosure will result in a reduced agent concentration and decreased period of protection.
The design and installation of a facility should include an examination of the enclosure to locate potential leaks. These may then be dealt with appropriately, usually by being effectively sealed. Codes [10, 11. 12] specify an enclosure integrity test to investigate the presence and magnitude of leaks.
Enclosure integrity tests check that the enclosure can hold the agent for a minimum period of time.
Experience has shown that enclosure integrity will reduce over the normal lifetime of an enclosure unless it is properly maintained.
For example, it will suffer if cable penetrations are disturbed or new openings are made to run additional cables. Since the design of extinguishing systems depends critically upon enclosure Integrity; it is essential
that enclosure integrity is maintained for the lifetime of the enclosure. Regular checks and a ‘permit to work’ scheme will help maintain its integrity.
The Integrity Test is based upon a descending interface being formed; in this case the extinguishant is discharged into the enclosure and gradually escapes through leakage paths around the perimeter being replaced by the ingress of fresh air forming a descending interface. The retention period is the time it takes for this descending interface to reach the tallest item of equipment requiring protection. Obviously the greater
the leakage area, the quicker the loss of agent, if this exceeds the allowable leakage rate, protection will not be fully effective for the tallest items of equipment over the recommended retention period.
If a ten-minute retention time cannot be obtained, the enclosure should be structurally sealed to reduce the leakage rate, restricting the loss of agent and enabling the retention time to be achieved. The enclosure should then be re-tested to confirm an acceptable level of Integrity has been achieved