| Clause | Recommendation | Justification for substitution |
5 | System actuation should be automatic by a glass bulb or fusible link, initiated by heat. | The system is actuated automatically by a “double-knock” smoke detector and verified through an infrared temperature sensor, not by a glass bulb or fusible link. The substitution results in a faster activation and avoids the water supply being overrun by excessive nozzles activating. It is proven for a number of scenarios, the measured activation times of a concealed sprinkler head are 2.0 to 13.7 times greater than those using an electronic nozzle system. A combination of an effective Response Time Index (RTI) of 20 m½s½ and an effective conduction factor (C factor) of 0.25 m½s-½ has been shown to reasonably predict activation times for an electronic nozzle system when simulated in a B-RISK zone model. |
6.3 b) | System design: The water mist system should be a wet pipe system (i.e. one that is permanently charged with water). | Hydra uses a dry-pipe unpressurised system on standby. The substitution avoids Escape of Water claims from tampering, legionella, corrosion and clogging. A wet pipe recommendation is logical for a mechanical automatic nozzle which takes longer to activate than an electronic nozzle. The time to fill the max piping length of Automist Hydra at 60m is 20 seconds and is used successfully on every fire test in Clause 6.1. |
6.3 c) | Thermally activated nozzles should have quick-response thermal elements in accordance with BS EN 12259-1 | Automist Hydra uses a combination of detection (to EN-54 or to BS EN 14604:2005) and infrared temperature sensing to initiate discharge. The substitution results in a faster activation and avoids the water supply being overrun by excessive nozzles activating. |
6.5 | System piping should be hydraulically designed to deliver the required water flow and pressures as determined by the fire tests in Annex C. | Automist is a pre-engineered system with a maximum total pipe/hose length of 60m i.e. the hydraulic calculations have been done by the manufacturer and are included in the DIOM. The substitution results in less work by the designer (and less chance of human error) in ensuring the water supply will be sufficient for the installed system because the manufacturer has done that already. |
6.6 | the system should be capable of providing pressures and flow rates to permit all the water mist nozzles in the fire test room or largest compartment, whichever is the greater, up to a maximum area of operation (AMAO) of 64 m2, to operate simultaneously | Automist is electronically controlled and it is programmed so that only one nozzle always operates. This substitution results in the assurance that the water supply only needs to be dimensioned for a single nozzle flow as there is no chance for other nozzles to involuntary discharge, increasing the demand for flow, which is expected to happen with a mechanical automatic nozzle, hence the existence of the clause. The substitution also gives assurance that no stored water is required for the installation given that the system will always only draw 6lpm. |
6.10.2.2 | Where nozzles are fitted within a sloping ceiling, nozzle positions should be determined by the pitch of the ceiling. | Automist has proprietary nozzle locations and coverage at approximately 1.3m height FFL and not on the ceiling, which is detailed in its DIOM. This substitution results in improved fire suppression performance, by discharging mist at the base of the fire without loss through the hot smoke layer adjacent to the ceiling. A better wording for clause 6.10.1 would be the one found in EN 14972-1 (note the term shall as a mandatory requirement): ‘For each application, the manufacturer shall prepare a detailed manual to provide a specification of the system information.
10) nozzle orientation, installation and positioning parameters;
11) requirements concerning obstructions (e.g. min. distance to beams, spray obstructions);
12) type of fire detection system (if used in the fire test);’ |
6.11.1 | Components should be in accordance with BRE publication LPS 1283 [N1], FM 5560, or another appropriate standard that can be shown to give an equivalent performance (e.g. a listed component in the LPCB Red Book Live [15]). | Automist Hydra has been third-party tested on all applicable clauses of BS 8663-1 (available in a separate document), following the same process as its product approval process being carried out in the US. This substitution provides the best publicly available evidence of performance given the lack of a component approval process in the UK to which Automist Hydra is accepted into. |
6.11.6.2 | All pumps should be designed to include an automatic test cycle where the pump is churned over at least monthly. | The Automist Hydra positive displacement pump is monitored but not churned monthly. This substitution is due to 1. The dry pipe nature of the system and 2. Pump seizure is a failure mode of centrifugal (low-pressure) pumps, not high-pressure positive displacement. A better solution still is the full system discharge carried out as part of the commissioning and annual service procedures. |
