Research undertaken by Imperial College London in conjunction with Edinburgh University and the SP Technical Research Institute of Sweden in 2014 found that fire is the second largest cause of incidents in wind turbines after blade failure. Considering the vast costs for constructing wind turbines, this statistic offers enough justification to consider specific fire prevention, detection and fighting questions.
Fires in wind turbines can start when flammable materials such as hydraulic oil and other flammable materials are in proximity to hot machinery or electrical equipment. Oils can catch fire if the gearbox or generator overheat, and high winds can potentially fan the flames. Lightening strikes can also spark a fire. Once started, the fire is unlikely to be brought under control due to the height of the turbines and the location of wind farms, which are normally a significant distance from the nearest fire services.
Measures can be put in place to protect against lightning strikes. Fire-resistant hydraulic fluids and lubricant oils reduce the likelihood of a fire and the latest wind turbine designs incorporate heat barriers to protect materials that can burn. It is also recommended that manufacturers use non-combustible insulating materials. Intumescent materials (materials that expand if exposed to fire and therefore choke the fire) can help to suppress fires at an early stage. Systems can be installed to continuously monitor the condition of machinery so that maintenance and engineering work can be undertaken in a timely manner and the system can be shut down before a fire develops.
Should a fire break out there are fire detection systems that can be employed in conjunction with fire suppression systems and an automated shut-off. If a fire were to break out whilst an engineer was working within the nacelle (the outer casing at the top of a turbine) a fire detector would also give an early warning.
Fire suppression systems that are triggered by rises in temperature or by fire detectors are fitted in some turbines. Gas suppression systems work best in airtight environments. However if the ignition source has not been eliminated the fire may reignite once the gas has dispersed. Systems that are able to extinguish flames with water, foam or powder have the disadvantage that they might damage equipment. Automated suppression systems might also have to be disabled while engineer work in the nacelle to prevent suffocation, inhalation or, in the case of powder, obfuscation (a powder discharge in a small room can blind the operator).
Precautions for maintenance workers
For the periods of maintenance work a portable fire extinguisher should be provided. However, in the document Workshop Report: Escape from the nacelle in the event of a fire, produced by the G9 Offshore Wind Health & Safety Association it states that ‘a fire extinguisher should be considered as an aid to escape rather than a primary means of fire control/suppression.’
Safelincs spoke with representatives of one of its customers, energy company Vattenfall, regarding the siting of fire extinguishers. The company has turbines from a number of manufacturers. In some cases the portable extinguishers are situated as a permanent fixture within the nacelle. In other cases the engineer will carry an extinguisher with him as part of his tool kit.
Recommendation from Safelincs
1) For permanently installed portable extinguishers:
The downside of standard fire extinguishers is that they require an annual service carried out by a qualified extinguisher engineer and a refill needs to be undertaken for most extinguishers after five years with the unit replaced after ten years. Since a visit to turbines by an external extinguisher engineer is usually hard to achieve, a service-free fire extinguisher is a better solution.
Safelincs can offer a range of service-free foam extinguishers in 2 ltr and 6 ltr sizes. These fire extinguishers are manufactured in the UK from non-corrosive materials and feature duplicate pressure gauges. They only require an annual visual check by any member of staff, e.g. the turbine maintenance engineer. They also do not require a refill after five years. Instead, after ten years they can be refilled and used for a further ten years.
The resistance to a corrosive maritime environment makes these extinguishers particularly well suited to the wind farm industry.
2) For extinguishers carried by the maintenance engineer:
The extinguisher in this case must be light, broad spectrum, safe for use on electricity, non-damaging to equipment and harmless in the case of inhalation. There must also be no risk of asphyxiation.
Safelincs can offer a range of portable water mist extinguishers, which can be used on grease, oils, electric equipment (up to 1000 Volt), fabric and plastics. The extinguishers create a very fine mist of de-ionised water that cannot conduct electricity. The inhalation of the water mist is not harmful and the mist does not leave a deposit.
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