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Watermist fire fighting MV electrical safety

David Gorshkov

I am reviewing the fixed watermist fire fighting installations in a new fleet of hybrid ships we are building . The water mist based fixed fire fighting appliances (FFFA) we are using extends into the main propulsion areas as well as the power generating areas.

Water Mist heads are used instead of sprinklers these days as these are more effective, however I can find no definitive tests or regulations that state water mist is safe to use in Medium Voltage switchboard areas?  Appreciate that if I have a fire the main objective is to extinguish it but it is not unusual for FFFA to be set off accidentally in a technical space so I must then consider IP ratings of equipments in these spaces in order that equipment is not damaged during an accidental discharge and that engineers investigating the incident are not at risk of electrocution from the MV systems which may still be live or charged!

Does anyone have any reference information regarding any testing done on Watermist systems to validate their safety levels with LV, MV and indeed HV systems?

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    Please try putting your question in the I.E.T's B.S. 7671 Wiring & Regulations forum. You will get answers there.

    I would ask the manufacturers.

     

    Z.

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    Based on my experience over the years on ships, water mist fixed fire fighting system have been designed to rarely activate accidentally based on two fire detectors simultaneously activating. That is, both smoke and flame detectors of the same zone/area must be active before the FFFA will release water mist to that particular area/zone. Furthermore, warning alarm precede the release of water mist to make time for evacuation. 

    The water mist system does cover/protect the auxiliary boiler area , the main engine, auxiliary engines area, incinerator area and purifier area. 

    Nonetheless, the IP rating of equipments in these areas must be of concern. 

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    Its the accidental discharge that causes the issues. I've had numerous accidental discharges via manual activation points for the hi fog as well as 2 smoke and 1 flame going off…..engineers LED torches are a source of activation as well….We are looking at dry pipe and glass bulbs as well as 2 smoke and 1 flame to help avert false alarm damage. We use this on the bridge and nav/comms equipment rooms so will be extending this to the propulsion rooms as well to cover the propulsion TX, VFD's and POD equipments. Class will accept IP32 in locked spaces  as  opposed to the main engine room space which of course is an issue if the WM goes off accidentally….and it will!  I'm also looking at mitigation of the IP32 cabinets…spray hoods and secondary doors to help limit any damage in the event of…..

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    Noted, it's the first time I am learning of 2 smoke and 1 flame detectors activation system for watermist FFFA. 

    With regard to accidental manual activation, the local and remote push buttons are usually protected with either plastic cover (breat-the-glass) or stainless steel plate cover to slide aside before the push buttons can be depressed to activate the system to prevent accidental release. 

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    All good precautions…still doesn't prevent accidents hence the need for secondary protection of the equipment from water spray if possible….

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