Carl Hunter and Scott Starr explain why fire suppression in wind turbines is so important and explore the challenges faced

WIND POWER is an exciting emerging sector that needs those of us involved in fire safety to get on board. As electricity generation becomes more reliant on renewable energy, wind power is increasingly important in the energy mix. With our reliance on wind turbines growing, keeping them fully operational and at reduced levels of risk is also more and more important, and consequently so is safety management. There are more than 340,000 wind turbines worldwide, yet the vast majority of turbines have no fire suppression system installed.
 
The fires in wind turbines not only lead to a loss of business continuity and a negative impact on the company’s reputation, but also they are a critical safety issue. Possibly harmful debris can drift into the wind and there is also a significant risk to human lives. When turbines are under construction, commissioned maintenance and repair, escape routes for operators are often long and vertical. 
 
A recent report found that three out of six incidents studied involved a human presence in the nacelle, the cover housing that houses all of the generating components including the generator, gearbox, drive train and brake assembly, and hence, a fire becomes a safety concern. In 2013, a crew of four engineers died in Ooltgensplaat, Netherlands, in a wind turbine fire. This calls for improved review of fire safety to minimise the risk to engineers.
 
Fire is the second leading cause of accidents in wind turbines after blade failure1. Most wind farms are in remote locations and wind turbines are designed with the mechanical portion – where most fires start – almost 300ft off the ground, at the top in the nacelle. There is simply no practical way to respond to a fire in these units, meaning that when one occurs, the typical action is simply to wait for it to burn out. 
 
Safety investment
 
With the average overall cost of a wind turbine fire around $4.5m2 and given that $112.5bn was invested in wind power globally in 20163, turbine owners and authorities are increasingly seeing the prudence of investing in fire suppression. Since 2011, there have been 36 large wind turbine fire incidents reported in the mainstream media, although the actual number is much higher, with many smaller, less visible fires going unreported. Most recently, in Wyoming, USA, last September, a wind turbine blaze caused a wildfire that burned out nearly 1,600 acres. 
 
There are three main causes of wind turbine fires: mechanical failure, electrical malfunction and lightning strikes. These pose a uniquely high risk due to both the turbines’ exposed locations and their height: turbines are now being built in excess of 450ft. Even a small fire can accelerate quickly in a nacelle that comprises highly flammable resin fibreglass. Internal insulation, which can become contaminated by oil deposits, further adds to the fuel load. 
 
Redesigning the turbines to reduce the fuel load inside the nacelle is one step to reduce fire risk. In addition, any maintenance and repair activities that involve ‘hot work’ inside the nacelle could be avoided. It has also been suggested that condition monitoring systems should be implemented and maintenance checks completed regularly. 
 
As a final step, automatic fire detection and suppression systems can be incorporated to further protect the nacelle. This presents a unique challenge, as dust, vibration and temperature fluctuations can all interfere with reliable operation. 
 
Detection and suppression
 
Several types of fire detection are available. Smoke detection or air sampling systems can be successful in detecting the early stages of a fire, but may be rendered ineffective by air flows and environment. Alternatively, traditional linear heat and fusible link detection systems aren’t affected by air and dust, but are potentially electrically conductive. All these systems will fail if the external power or battery backup fails. 
 
Then there are the fire suppression agents. Compressed air foam systems and water mist are potentially corrosive and can be ineffective on energised electrical components. Carbon dioxide systems aren’t ideal because, due to the CO2 displacing the oxygen in the event of a discharge, the fire suppression system has to be ‘locked out’ any time personnel are present in the nacelle. In such a situation where people are working at height, this is a major safety concern. 
 
In the cramped environment within the nacelle, a problem can also be posed by the weight of these technologies and the space required to store them. The most common solution today overcomes these drawbacks by providing component level automatic systems that offer both fire detection and suppression in a single package. Designed to detect a small fire in or around a critical component, they dramatically improve the response time and reliability, while reducing the size of the system required. 
 
They use clean agent fire suppression technology involving a non conductive gas, which leaves no residue following a discharge, requires no clean up, and in small volumes does not present a hazard to personnel. The presence of an automatic fire detection and suppression system such as Firetrace offers 24/7 reliability and unsupervised protection to quickly address a growing fire and limit its damage. And yet, despite the availability of affordable fire suppression methods, thousands of wind turbines are still being installed without adequate fire protection, and entirely preventable wind turbine fires continue to occur. 
 
Legislation growth
 
There has, however, been increasing momentum over the past few years for legislation requiring fire suppression on new wind farms. A growing list of authorities in Germany, and a number of both local and state governments in the US, are acknowledging that fire suppression is a judicious step to safeguard assets in the event of a fire in a wind turbine. A piece of unique regulation in Canada has taken it a step further, enabling local authorities to insist that fire suppression is retrofitted to existing sites.
 
This is a welcome trend. Designing in fixed fire suppression, which can contain the blaze within the micro environment of the nacelle, is a logical move to help prevent large scale fires. But it is important to note that such fire extinguishing systems require maintenance to ensure they are fully operational and ready in event of a fire.
 
ISO 14520-1: 2015(E) assumes that these systems accidentally discharge and leak, with section 6.2.4.2 (Contents indication) stating: ‘Means shall be provided to indicate that each container is correctly charged.’ This is followed by: ‘9.2.1.3 The storage container contents shall be checked at least every six months as follows: a) Liquefied gases: for halocarbon agents, if a container shows a loss of agent in quantity of more than 5% or a loss of pressure (adjusted for temperature) of more than 10%, it shall be refilled or replaced.’
 
Meanwhile, section 10.5.3.2.2. of NFPA 850 states that the maintenance and inspection of total flooding gaseous agent systems and interlocked equipment are critical. All systems at some time may be called on to operate in an emergency situation, and may help in saving life and property. It is for this reason that knowledge that the system can operate to its full potential is so essential.
 
However, are annual checks sufficient in risky environments? What if the suppression systems installed in the turbines to protect life and infrastructure do not release on actuation? 
 
Gaseous extinguishing/suppression systems are installed to protect against special hazards in critical infrastructure as their main objective. They deliver the infrastructural resilience that wind turbines require. If it is a known fact that there is a long response time to wind turbine fires, then it is unacceptable that the dynamic suppression systems are left unattended for 364 days a year.
 
Constant monitoring 
 
A dynamic system needs monitoring. The reality is that gaseous systems are checked for contents annually because they are pressurised and anything that is dynamic offers risk of loss of contents, but this fails to deal with the probability of discharge or leakage for the 364 days per annum in the interim between certification checks. If the hazard is special and the infrastructure critical, then this is the case for the constant monitoring of the suppression systems that aim to deliver their protection. Inspection should include an evaluation that the extinguishing system installed continues to provide adequate protection for the risk.
 
Coupled to this is a complete lack of room integrity testing after the gaseous system has been installed. As buildings age or their internal use is changed, leak sites develop. If the gas cannot be ‘held’ in the room on discharge during a fire event, the probability of its suppression diminishes in direct proportion to the size of the leak sites. Room integrity tests are imperative for the determination of both the hold time and the peak pressure needed for successful fire suppression. 
 
The level of leakage is carefully monitored to ensure the correct agent concentration is achieved: room integrity must be ‘tight’ enough to ensure sufficient retention time according to NFPA Standards or ISO 14520, yet remain ‘loose’ enough to prevent enclosure damage at discharge. The presence of undesired and unregulated leak sites reduces room integrity and will hence dramatically impact the hold time and peak pressure, placing room contents and potentially wall structures at risk. 
 
It is accepted that in wind turbines, vibration can loosen connections, while dirt, dust, and temperature extremes are known to cause unwarranted discharge. Additionally, openings in the turbine housing significantly inhibit achieving the designated agent concentration. Devising a solution to overcome these challenges can add significantly to the weight in the turbine.
 
For regular inspection, there are solutions such as the Portalevel MAX, a handheld ultrasonic liquid level indicator which can service a cylinder in 30 seconds (in contrast to 15 minutes by traditional manual weighing) with accuracy of up to 1.5mm off the true liquid level. 
 
Smart solutions enable wind turbine owners and operators to improve their fire safety management, reduce the risks to human life, ensure business continuity caused by any downtime and minimise risk to reputation by delivering a safe site.
 
Case study – Palm Springs, California
 
A FIRE at a site in Palm Springs, California, cost more than $243,000 in damaged equipment and downtime, prompting owner Whitewater Energy Corporation (WEC) to turn to Firetrace and its automatic fire suppression system, comprising unique linear pneumatic detection tubing, routed throughout the equipment. 
 
In late 2009, the system was installed in all six turbine converter cabinets and, in a later fire that started in a wind turbine converter cabinet, it activated immediately on detecting the fire. It released its suppression agent directly on the heat source to contain the fire and limit damage to the eruption point. No damage was caused to the cabinet or internal components, other than the failed component. 
 
Firetrace was able to quickly deliver a replacement system, enabling the turbine to be up and running the next day. This was a considerable improvement on the average downtime following a wind turbine fire of approximately nine months. 
 
Additional safety
 
Coltraco’s Permalevel Multiplex, a fixed fire suppression monitoring system, is also designed to prevent fire suppression systems at risk of accidental discharge from affecting the effectiveness of the overall fire protection system in the event of a fire.
 
The system is designed for continuous contents verification and with guaranteed systems operations, adaptability for purpose, 24/7 remote access to the systems status, an uninterruptible power supply and remote real time monitoring, it can offer the efficiency that is needed in a wind turbine.
 
Carl Hunter is managing director at Coltraco Ultrasonics, and Scott Starr is marketing director at Firetrace International. For more information, view page 5
 
References
  1. Report by Imperial College London, University of Edinburgh and SP Technical Research Institute of Sweden in Fire Safety Science, 2014.
  2. Renewable Energy Loss Adjusters.
  3. Bloomberg New Energy Finance.

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