Enclosure integrity testing for fire safety

Clean agent fire suppression systems are used in enclosures where a sprinkler system would cause damage to sensitive contents such as computer servers, paper files or historical artifacts. Upon fire detection the compressed clean agent (which can be a halocarbon or an inert gas) is released into the enclosure. Once the enclosure is totally flooded, the agent will begin to leak out at a rate that primarily depends upon leakage area in the lower part of the enclosure, although higher leakages play a significant role as well.

This is due to the fact that most of the gaseous agents (except nitrogen) are heavier than air. If the enclosure has leakages, the gas starts leaking out from the enclosure and fresh air replaces the gas from above.

The gas suppression system is designed to protect critical systems within the enclosure for a certain time once the agent is released, which is called the ‘hold time’. This will generally be 10 minutes, or in some cases 20 minutes or any other time frame dependent on the exact situation and used standard. To keep the agent inside the enclosure, the enclosure will have to be air tight enough to prevent agent from leaking out too fast: the less leakage, the more hold time an enclosure will have.

Apart from agent loss due to leakage, the other significant factor one must consider while designing the rooms with clean agent suppression systems is Peak pressure. Once agent is released within an enclosure, the pressure in the enclosure will go up, and a peak pressure will be reached (before the start of the required hold time). For inert agents (such as nitrogen and argon) a positive peak pressure is reached due to the large quantity of agent that is released from a highly pressurized cylinder. For halocarbons (such as HFC-227) both a negative and positive peak pressure will form due to the cooling effect caused by a phase change of the agent (negative pressure), as well as the nitrogen (pressurizing agent) blowout at the end of the discharge (positive pressure).

The peak pressures, both positive and negative, can be high enough to severally damage the enclosure. Damages done can vary from cracks in structures to completely blown out walls, doorframes, and ceilings. Once the damage is done, the agent will leak out of the enclosure and the fire will not be suppressed as intended.

The room integrity test is assessed with blower door test. This test is used to measure the leakage of an enclosure. Based on the leakage, the software predicts the hold time and peak pressure performance of the rooms equipped with clean agent suppression system.  Door fan test will calculate the results considering the worst-case scenario, it draws the air through leaks that are present at upper as well as lower portion of enclosure to predict the descending interface of the suppressing agent. The time required for the agent to fall till minimum protected height defines the concentration hold time.  

This test is mandatory as per NFPA 2001 and ISO 14520 standards.

Integrity test is required to be performed during the commissioning and annually or if any major changes are made (whichever comes first).

Buildingdoctor DMCC has Retrotec Level-3 certified enclosure integrity testers.

Keywords: Enclosure integrity test, NFPA 2001, ISO 14520, peak pressure, clean agent suppression commissioning. 

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