All gas extinguishing system standards require a certain concentration of extinguishant to be maintained in an area for a minimum time period, generally 10 minutes for clean agents.
Discharge testing on electrical and mechanical fire extinguishing systems was originally performed to test reliability and validate extinguishing concentrations. However, as installation and equipment manufacturing standards became more stringent and quality management systems became the norm, it was found that reliability of the systems began improving; and statistical measurement techniques as required by ISO 9000 highlighted problem areas sufficiently to implement timeous corrective actions should problems occur.
Meanwhile the discharge test only verified a design for that particular system configuration at that particular point in time. Also when performing a discharge test, only a few seconds are available to establish where a problem may have occurred if the design concentration is not reached, and further expensive discharge testing is then required. Concerns over depletion of the ozone layer and global warming further curtailed the use of halon and other synthetic gas systems. As a result, enclosure integrity acceptance testing was adopted in its place.
Room integrity testing
Room integrity testing is a mandatory requirement of gas extinguishing standard SABS/ISO 14520. This standard also states that the testing must be carried out every 12 months to validate the enclosure integrity. Failure to perform the initial room integrity test is a violation of the SABS design and installation code, and places system performance responsibilities clearly on the installation contractor. Failure to perform annual testing places system performance responsibilities on the shoulders of the end-user.
The test consists of pressurising the enclosure with calibrated fans that provide specific airflows at specific flow pressures. In addition, the exterior and interior pressures of the enclosure are monitored so as to determine air leakage from the room. The earlier NFPA 2001 standard only requires a single measurement to be performed, while the SABS/ISO standard requires multiple sets of test data to be recorded. The SABS/ISO requirement is therefore more accurate and can highlight equipment errors and prevent operator manipulation of the results, since the minimum correlation factor and allowable standard deviation is specified.
The test result is provided as an equivalent leakage area (ELA) in square metres. This is the sum total of leakage paths in the room. By utilising a computer model of the gas extinguishing agent properties and knowing the ELA, the gas extinguishing retention times for the minimum design concentration can be determined.
If the retention time is greater than 10 minutes, then the room passes. If a room fails, it is easy to locate the leakage paths using smoke pencils and seal the leaks. Enclosure integrity and the fire resistance thereof is also a requirement of BS 6266. This standard is implicitly referred to in BS 5839, which has also been adopted in South Africa as SABS 0139 (now SANS 10139).
Why perform room integrity testing?
1. Room integrity testing is a mandatory requirement of the SABS/ISO clean agent standard. This applies to all gases and all systems.
2. Although not mandatory, it is highly recommended that room integrity be performed on CO2 installations. CO2 has one of the highest densities of any extinguishing gas and so has one of the highest column pressures. This means that it is one of the most difficult gases to maintain at the correct concentration and the retention times are typically 20 minutes – twice as long as clean agents.
3. Extinguishing concentration measurements in a discharge test generally overestimate the actual extinguishing concentration by a substantial margin. The results can easily create a false sense of security.
4. Room integrity testing allows the total room leakage to be identified and if this leakage is too great, remedial action can be taken immediately and the results of the remedial work checked.
5. One of the most important design aspects of all clean agent systems is correct room venting. This is especially true of CO2 systems. High discharge rates of the synthetic gases and high air displacement of the inerts (±40%) make venting a key issue. With too little venting the room can be subjected to overpressurisation, which will result in structural failure. With too much venting the gas extinguishing concentration may not be achieved for the prescribed time period. Room integrity testing allows the venting requirements to be verified by on-site testing.
6. There are major savings in the running costs of air conditioners.
For more information contact Sam Wright, Alien Systems and Technologies, +27(0)11 949 1157, [email protected], www.astafrica.com
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