Fire detection on Electric Mountain

Industrial environments are among the most challenging applications when it comes to designing and specifying a modern fire detection system. When much of that industrial environment is also situated underground, it becomes a unique and fascinating project.

Such was the challenge facing First Hydro Company at Dinorwig Power Station in North Wales – known to thousands of visitors as Electric Mountain – when they needed to upgrade the facility’s existing conventional fire detection system to meet current safety requirements.

The site

Hidden deep inside Elidir Mountain, close to Snowdonia National Park, Dinorwig is a pump storage hydro electric power station. Operational since 1984, it supplies electricity to the national grid on a daily basis as well as providing back-up for periods of heavy demand. In fact, Dinorwig offers one of the fastest response times of any power facility in the world, generating 1,728MW from standstill in just 90 seconds.

This amazing feat is achieved using the natural force of seven million cubic metres of water released from Marchlyn Mawr, a reservoir situated 636 metres above sea level, to drive massive turbines. The released water plummets some 568 metres – 11 times the height of Nelson’s Column – before entering six separate inlet valves leading into the turbines.

The natural force of the water turns each turbine, which in turn is connected to its own generator. The generated electricity is then boosted to 400,000 volts by the station’s transformer network before being transmitted to the nearest substation, where it is fed into the grid. The spent water is collected in Llyn Peris, a lake at the foot of the mountain, and pumped back up to Marchlyn Mawr reservoir for reuse.

A truly remarkable piece of civil engineering, virtually all the tunnels, pipes and generation plant at Dinorwig are located 750 metres inside the mountain.  In addition to being underground, some of the main areas requiring fire protection are truly monumental in scale: the machine hall, for example, is 180 metres long, 23 metres wide and 51 metres high.

Fire protection challenge

The project to upgrade the power station’s fire detection system was led by an in-house team from First Hydro Company. Andrew Taylor, Technical Officer, explains: “We commissioned an independent fire risk assessment of the site to include areas that were not currently covered by the existing system. One unique aspect of this site is the requirement to link disparate buildings together, above and below ground.

“Another major factor is the pattern of air flows underground, influenced by the two main access tunnels and ventilation shafts above the subterranean power station. Smoke tests were undertaken to determine the type of fire detection technology and optimum location for the detectors under these circumstances.”

The height of the main cavern was also a potential issue. The fire detection system would have to take into account CDM regulations regarding working at heights to ensure that maintenance could be safely undertaken.

Based on this information, First Hydro Company developed a specification that would deliver:

  • a networked fire detection system to cover above-ground and underground areas of the power station sited several kilometres apart;
  • be based on an open protocol;
  • include aspirating fire detection.

Kentec Electronics Limited was one of the specialist fire detection companies that were asked for input at an early design stage. Working in partnership with Apollo Fire Detectors Limited (whose devices were used in the original conventional fire system at Dinorwig), Kentec invited representatives from First Hydro Company to a presentation at its head offices in Dartford, Kent, which clearly demonstrated that a fire detection system based on Apollo’s open digital protocol would fulfil their requirements.

Local contractor Lloyd Morris Electrical Limited was appointed to install the Kentec/Apollo fire system. Because the power station is in constant use, installation of the new equipment had to take place in parallel with the old fire system to ensure no loss of cover. In addition, the unique site environment meant that the new fire system would have to incorporate detection and extinguishing equipment from several different specialist manufacturers.

Apollo’s protocol was a significant factor in meeting these requirements. Because it is open, it allows fire detection products from different manufacturers to be incorporated into the same system. As it is digital, it also offers security of transmission. In addition, the availability of interfaces based on this protocol enables other systems to be linked seamlessly with the new fire system.

Under control

The new Dinorwig fire detection system is based around 12 Kentec Syncro analogue addressable control panels – eight of which are installed underground. Available with two or four detection loops, each capable of hosting up to 126 Apollo devices, Syncro panels use modern microprocessor technology to provide a control system of extremely high integrity and are certified to EN54 (parts 2 and 4).

There are four major links to network the control panels at Dinorwig together, the longest of which runs for nine kilometres from the underground power station to a switch-room near the upper reservoir. Richard Hackett, Sales Manager for Kentec, says: “Standard copper cabling is no use in circumstances like this so single mode fibre optic cable was used to link the panels over the longer distances required. The Dinorwig 9km link is certainly the longest we have ever been involved with, but it works beautifully.”

The new fire system also includes three strategically-sited graphic panels based on Kentec’s GUIDE system, which allows the fire control panels to provide a single point of co-ordination for all alarms. These are positioned in the main control room and the pressurised cabin (an incident control point), both underground, and at the main gatehouse.

Providing a first point of contact for staff and the fire brigade in case of emergency, the graphics panels feature a standard Windows look and feel and run under Windows® 2000 or XP. Users can select maps, text, photographs, audio or a combination of all as required and zoom in on an individual device to pinpoint an alarm or fault. The system can also be programmed to send automated email alerts to maintenance and engineering staff. A comprehensive history logging and reporting system allows analysis of events and trends to be identified to reduce unwanted alarms.

Fire detection

Over 1,500 Apollo XP95 fire detectors and ancillary devices were specified to meet the general fire detection requirements for Dinorwig. Optical smoke detectors are used in the main areas and approach tunnels, with heat detectors protecting rest rooms and kitchens where transient high levels of smoke or steam could otherwise trigger a false alarm. In excess of 450 addressable sounders and sounder beacons are strategically positioned throughout the facility to alert staff to an emergency and around 250 manual call points enable employees to raise an alarm.

In the main cavern, an aspirating fire detection system has been fitted so that air turbulence will not affect the system’s ability to accurately detect any problems.

Andrew Taylor of First Hydro Company comments: “By and large, we were able to use standard fire detectors from Apollo’s range to achieve the reliability levels we required in our subterranean environment. This helped to control costs and timescales on the project.

“The inclusion of aspirating fire detection could have been an issue in integrating different systems from different manufacturers, but the choice of an open digital protocol – plus the fact that Apollo offers an interface that enables aspirating fire detection to be linked in – avoided any compatibility problems.”

Water spray and gas extinguishing systems are also installed in the transformer rooms at the power plant. Approximately 100 Apollo interfaces enable this equipment to link in to the main fire detection system.

Evacuation

Although the power station is highly complex in its fire detection requirements, the evacuation principle is simple: one alarm, all out – except a few essential staff in the control room.

“Smoke is the main concern underground and there is simply no point in taking a risk,” says Andrew Taylor. “We also run regular tours for the general public so we are dealing with people who are unfamiliar with the site layout. Staff working above ground evacuate at the same time to the same marshalling points so we can account for everyone in an emergency.”

Using the old system of sirens as a warning underground didn’t meet the latest recommendations on sound levels. The new fire system is able to provide reliable noise dispersal, with loop powered sounders and sounder beacons in the machine hall where noise levels may prevent audible alarms being heard.

Conclusion

The fire detection system at Dinorwig now offers comprehensive coverage across the entire site. Thanks to Apollo’s open digital protocol, the point fire detection, aspirating detection and extinguishing systems are fully integrated. Kentec’s sophisticated graphics controls provide a user-friendly interface that enables routine maintenance issues and sources of alarms to be pinpointed and responded to effectively.

Andrew Taylor concludes:

“The new fire system certainly gives us peace of mind that Dinorwig power station is protected from fire hazards and that we can get everyone out should an incident arise.”