Guidance Note Watermist Fire Protection of Plant Rooms
SCOPE This document sets out the requirements for protection of plant rooms with watermist systems and should be read in conjunction with BS8489-1. PLANT ROOM CLASSIFICATION Plant rooms are facilities providing building services such as water, electricity, heating and HVAC within or adjacent to buildings. The fire risk within plant rooms is complex and varied, and in order to ensure that a suitable suppression system is selected, a risk assessment should be undertaken at the design stage by a suitably qualified competent person. Generally, plant rooms can be classified as below. Low fire load plant rooms Low fire load facilities characterised by non-combustible ducting and/or limited electrical cabling. These facilities contain no storage. High fire load plant rooms High fire load facilities characterised by combustible ducting and/or significant electrical cabling. These facilities contain limited storage. Machinery space plant rooms High fire load facilities characterised by machinery such as combustion engines/boilers or other equipment, using fuel and/or lubrication fluids less volatile than or equal to heptane, and incidental use or storage of limited quantities of flammable liquids of not more than two 55 gallon (208 litre) drums. When selecting the plant room classification, the assessment must be made on the worst case risk. 2 of 5
APPLICABLE FIRE TEST PROTOCOLS Nozzle performance characteristics and spacing criteria should be determined by full scale fire testing to one of the below applicable fire test protocols. Plant Room Classification Low fire load plant rooms Applicable Fire Test Protocols BS 8489-7 FM 5560:2016, Appendix G High fire load plant rooms VdS 3188 Annex K1.6 Machinery space plant rooms BS 8489-5 Machinery spaces <80m 3 FM 5560:2016, Appendix A Machinery spaces <260m³ Machinery spaces >260m³ Pool and spray fires local application VdS 3188 Annex K2.2 FM 5560:2016, Appendix C FM 5560:2016, Appendix E BS 8489-4 FM 5560:2016, Appendix I 3 of 5
RESTRICTIONS Storage of combustible liquids, gases or other highly flammable substances in plant rooms is not permitted. With the exception of machinery space plant rooms where storage of no more than two 55 gallon (208 litre) drums of substances less volatile than, or equal to heptane, is permitted. ASSUMED MAXIMUM AREAS OF OPERATION Low and high fire load plant rooms shall be designed taking into account an assumed maximum area of operation (AMAO) of at least 144m². Machinery space plant rooms shall be designed as a total flood system, taking into account all nozzles within the risk. HYDRAULIC PIPEWORK CALCULATION System piping shall be fully hydraulically designed, taking into consideration the entire piping system, to deliver the minimum required water flow and pressure to the AMAO. OBSTRUCTIONS Obstructions in plant rooms usually take the form of either ducts or cable/pipe trays/racks. They can create physical barriers to the distribution of mist by removal of mist due to droplets coalescing on them, as well as by impairing the distribution of the watermist droplets. Nozzles produce a wide range of spray patterns and spray velocities. The degree to which obstructions can affect the performance of any particular nozzle will differ, according to the spray technology and type of obstruction. Where watermist protection is delivered through open nozzles, obstructions are largely overcome through the delivery of a uniform mist density through the plant room surrounding obstructions. In all instances and to ensure that there is an even watermist spray pattern, minimum head centres must be maintained. Where this cannot be achieved due to either vertical or horizontal obstructions, additional spray heads should be added. However, where automatic nozzles, successfully tested for this application are used, the testing should provide a determination of nozzle positions in relation to obstructions. Ducts normally pose no fire threat but can remove mist and/or block distribution. Nozzles should be positioned to compensate where mist loss from nozzle deliveries is likely to occur. Cable and or pipe trays/racks may pose partial obstruction of mist distribution. The cables may pose a fire hazard in themselves. Watermist solutions can take the form of: Placement of nozzles on either side or the trays/racks to discharge onto and under the trays/racks. Placement of nozzles above and below the trays/racks. 4 of 5
DISCLAIMER The information set out in this document is believed to be correct in the light of information currently available but it is not guaranteed and neither the Fire Industry Association nor its officers can accept any responsibility in respect of the contents or any events arising from use of the information contained within this document. Tudor House, Kingsway Business Park, Oldfield Road, Hampton, Middlesex TW12 2HD Tel: +44 (0)20 3166 5002 www.fia.uk.com 5 of 5