Meridian has been asked by several companies recently to answer some fire safety code questions and anytime good questions come up, we always like to share what we have found with everyone else. A fire safety question that has come up more than once over the last month is when a space protected with a clean agent suppression system is equipped with a self-circulating HVAC unit, does that unit have to shut down in the event of an agent discharge?

This is a fair question, because up until the last few updates of NFPA 2001, you could leave it running. The position had been if the air is recirculating with no exhaust and no means to bring in fresh air, than leaving the unit run, in theory, should have no net impact on the concentration of agent so long as any volume of associated ductwork outside the protected space was accounted for.

However, the school of thought on this has changed over the years. Testing has shown that when the air is continuing to recirculate that many volumes can see an increase in leakage rates of clean agents. One example of this is it’s not just potential leakage along the floor level that can have an impact, but everywhere within the space (and associated HVAC equipment) when the units continue to circulate air. There are other considerations as well, but in 2008 and continuing in 2012, the NFPA 2001 requires that unless the equipment is necessary to ensure the safety of personnel, all forced air ventilating systems, including self-contained air recirculation systems, shall be shut down or closed automatically, unless it can be shown that their continued operation will not adversely affect the performance of the extinguishing system or result in the propagation of fire. (NFPA 2001, 2012 edition, 5.3.6 – 5.3.6.2.)

Over the coming weeks we are going to look at some additional “new” rules of the 2012 edition of NFPA 2001 and impact they will have on clean agent systems. So be sure to check back for that.

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