Halon replacements: ensuring enclosures will hold new extinguishants
by Paul Jennings

Halon 1301 was the king of gaseous fire extinguishants. It was reliable and robust, very effective at putting out fires in vital installations, usually business-critical Comms and Computer facilities.

Even when the system was poorly designed, the enclosure was defective or the application was inappropriate, Halon 1301 would almost always put out a fire. Unfortunately the characteristics that made Halon 1301 such an excellent extinguishant also meant that it was very good at breaking down atmospheric ozone. Hence the death of Halon 1301 is imminent and replacement fire protection systems are now required. In Europe this means that from the end of 2002 a Halon 1301 system must not be refilled in the event of a discharge, and by the end of 2003 all Halon 1301 systems have to be decommissioned, with only very limited and tightly defined “essential use” systems being exempt.

For applications where gaseous fire protection is still required – which is most of them – there are a variety of inert and hydrocarbon replacement extinguishants available. ArgoniteTM and InergenTM – and of course Carbon Dioxide – are the principle inert agents, whilst FM200TM and FE13TM seem to be the commonest hydrocarbon replacements for Halon. We also await Novac1230TM, a new gaseous extinguishant from 3M, which should be completing approvals in the very near future.

For long-term solutions, the inert agents and NovacTM probably have the edge, as they have little or no Global Warming Potential. However in the short term the much smaller quantities required with hydrocarbon agents means that installing replacement cylinders is often much easier.

Whatever the extinguishant, it requires a satisfactory enclosure to be effective. A poorly built or maintained protected facility will compromise the protection provided by the gaseous extinguishing system. Gaps in fire barriers, holes around ducts, cable entries and pipe penetrations, missing sealant at junctions between elements, such as where a partition wall rests on an uneven floor slab – they all potentially allow the extinguishant gas to leak away too rapidly. Potentially, this could allow a defective cable or a jammed fan belt (for example) to re-ignite or continue to burn.

Moreover, with the inert agents, lack of pressure relief venting can be even more catastrophic. When we rapidly discharge up to 50% by volume of gas into an enclosure, the air it displaces has to go somewhere. In most installations, this will generate a major pressure spike that can be very damaging – in the past doors have been blown open, partition walling has been demolished and even blockwork walls have been breached at joints and weak points. Apart from the risk of flying debris and shock affecting both staff and equipment, any such event will massively increase the leakage rate from the enclosure and almost certainly mean that the extinguishant system does not put out a fire.

Overall, replacement gaseous extinguishants for Halon 1301 are substantially less robust and reliable. Indeed research from the United States over the first decade of clean agent halon replacements revealed that 59% failed when discharged in anger. The No. 1 cause of failure, also the principle cause of Halon 1301 discharge test failures in the past, was TOO MUCH LEAKAGE. Other causes of failure were wind-induced excess loss and over-pressurisation damaging enclosures.

All these potential problems are identified in an Enclosure Integrity door fan test. Moreover, protected enclosures only ever get more leaky over time, primarily because additional cables are installed without remedial sealing. Best practice now requires protected installations to be tested prior to handover, followed by annual repeat integrity testing to guarantee the enclosure is satisfactory.