A threatening cable fire occurred in a power plant’s boiler facility, causing a rather long business interruption. The fire started by slowly smouldering. The fire detector set off the fire alarm and, due to the process disturbance, the boiler was shut down in a controlled manner. Operating staff performed initial fire extinguishing with a powder extinguisher, while the factory fire department and the municipal fire department continued quenching the fire using fogfighters. The fire was quenched in approximately half an hour and the facilities were ventilated.
The fire started at a cable concentration point, which included different types of cables, and spread upwards along the cables, all the way to the ceiling, destroying the cables and electrical installations of the boiler facility. Since the cable lead-throughs were appropriately made and resistant, neither the fire nor the smoke were able to penetrate into adjoining electric rooms, which were also overpressured. The probable cause of the fire was a rise in the temperature in the cable concentration, and may also have involved some special damage to a cable or a loose joint.
Why is an electrical fire usually extensive and destructive?
In electrical fires, cables are usually of great importance: cable installations offer fires a good path along which to spread, as does a dusty, dirty or otherwise ignition-prone environment. When burning, the PVC in cable insulation and cable shells generates hydrogen chloride which, when it reacts with air humidity, forms hydrochloric acid, in turn causing serious damage to equipment and structures. The fire gases of PVC fires are extremely toxic for humans. Furthermore, electrical fires usually lead to long business interruption periods.
When is it worthwhile to perform loss prevention measures?
Loss prevention measures can and should be performed during all stages of the establishment’s and cabling’s life cycle. It is least expensive to take them into consideration in the planning stage: the location of electric facilities, construction solutions, compartmentation, protective systems and maintenance have a significant impact on loss prevention and risk reduction. Nevertheless, it is possible to improve fire safety at any point in time: even one successful loss prevention measure may cut a chain of events which could lead to a major loss.
Impact of choice of cable
Fire safety can be significantly influenced by the choice of cable. All various types of cables are available as halogen-free. Using them means that
- the fire gases do not cause corrosion
- the fire gases do not poison people
- visibility is maintained at the site of the fire
In addition, in power supply and control of all important functions such as safety systems, fire doors and smoke venting, fire resistant cables should be used.
Loss prevention measures
- Conducting regular inspections of electric equipment has proven to be the most efficient way to prevent electric fires.
- Thermogaphic scanning of electric equipment is an excellent and cost-efficient measure and can also be applied to cabling.
- Vertical cable installations should be cut off with fire stops in intermediate levels, since fires along vertical cables have a tendency to spread quickly.
- An automatic sprinkler system is the ideal for the protection of various cable spaces, cable concentrations and layers, as well as cable tunnels.
- Quick detection of cable fires requires an automatic fire alarm system equipped with a smoke detector; an aspirating smoke detection system is still better.
- A suitable sealing system for cable penetrations must be in use and the penetrations must be sealed so that the fire separation corresponds to that of a wall.
- A smoke and heat exhaust ventilation system (SHEV), either manual or automatic, must be installed in cable spaces.
- Access to cable spaces must be arranged so that fire fighting is possible.
- Of the various installation methods, surface, tray or (low) channel installations are to be preferred, along with conduit and duct installations. Tunnel installations or any other cable carpet or bunch left in a hidden space usually generate problems in fire extinguishing unless an automatic sprinkler system has been installed.
- Cable joints should be avoided.
- The cables that are no longer in use shall be de-energized and completely removed from their place of installation; otherwise, they will increase the fire load, prevent other cables from cooling down, make it more difficult to install new cables and constitute a load on cable trays.
Pentti Kautto, Inspecta
Ville Valta, If
