water mist
CEN water mist standards Although water mist is the system of choice for shipping, with test protocols available from the International Maritime Organisation (IMO), the IMO standards are not usually accepted for shore-based applications thus, confirms Alan Brinson, Executive Director of EFSN, water mist has to develop suitable standards.
When water mist first appeared on the fire protection scene 30 years ago it was being proposed as an alternative to halon and as a system that weighed less than sprinklers to protect shipping. To be accepted it had to prove its performance in those applications. When it came to cruise ship and ship machinery space protection, this was done by first establishing what performance sprinklers deliver, then showing that water mist could match or better it. These applications are now well-defined and water mist is the system of choice for shipping, with test protocols available from the IMO but these standards are not usually recognised for land-based applications so to compete with sprinklers in this much larger market, water mist had to develop appropriate standards. CEN Technical Committee 191, Working Group 10 is responsible for drafting water mist standards. It has divided its work into three parts: a design, installation and maintenance standard; fire test protocol standards and component standards.
Design, installation and maintenance
EN 14972-1 is the design, installation and maintenance standard for water mist systems. It was recently published and provides general guidance but is not as detailed as the sprinkler system design standard. This is because the characteristics and hardware of water mist systems from different manufacturers differ so much that many design criteria could not be standardised in a prescriptive manner. Instead, as for IMO, acceptable performance must be verified in representative full scale fire tests and, hence, fire test protocols for different water mist applications are being standardised. The different fire test protocols form the rest of the EN 14972 series and the results are linked to EN 14972-1 to set minimum design criteria. EN 14972-1 also has requirements for acceptable water supplies, alarms and facilities for periodic testing of the system. As well as design guidance for water mist systems that are alternatives to automatic sprinkler systems, EN 14972-1 covers deluge applications and the design of water mist as an alternative to gaseous extinguishing systems.
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outlook
In many areas EN 14972-1 refers to the manufacturer’s design installation, operation and maintenance (DIOM) manual. This term is used over 90 times in the standard and among other things the DIOM manual should set out design criteria for minimum operating pressure and nozzle pressures, nozzle spacing and orientation, maximum room dimensions, obstruction criteria, water quality and hydraulic calculations. These are essential inputs to the performance of the system. As they are not in EN 14972-1, the DIOM manual should be verified and approved by an independent third-party laboratory which has expertise in water-based fire protection systems. It is against CEN (and ISO) rules to call for third party approvals in a standard but such approvals greatly increase acceptance of a technology, particularly by insurers and help to open up markets to it.
Fire test protocols
While performance-based fire tests exist for sprinklers in storage applications, sprinklers have historically not been put through full-scale fire testing for most less challenging applications, so the first step for water mist was to devise a set of fire tests representative of the application and run them with sprinklers. In deluge applications there was no need to compare with sprinklers so absolute rather than relative performance criteria were established. Each fire test protocol includes full-scale tests devised to be representative of the application to be protected, while also being repeatable and reproducible. WG10 decided not to reinvent the wheel so most of the 16 fire test protocols now published or planned are based on existing protocols from FM Approvals (seven protocols), VdS (five protocols), BS (two protocols) or UL (one protocol). Only one protocol is completely new. So far three water mist fire test application protocols have been published: EN 14972-16 for industrial oil cookers EN 14972-8 for machinery spaces exceeding 260 m3 EN 14972-9 for machinery spaces up to 260 m3 These are deluge system applications, representing relatively small markets. By contrast EN 14972-3, a fire
