Turbine lube oil fires can be physically and financially devastating, but they don’t have to be. Proper fire protection can safeguard a facility from such fires.
Picture two home improvement superstores, side by side. Imagine an open-floor turbine building that size. Now, imagine burning it to the ground. At today’s average value of $2,200 per square foot, you’d be looking at nearly $410 million going up in smoke. That’s the amount of money a group of power-generating companies recently lost in property damage due to catastrophic turbine lube-oil fires.
Each company suffered approximately $24 million in property damage. They were out of business more than six months, on average, and lost generating capacity exceeded 20 million megawatt hours. As a result of these fires, three turbine units were retired prematurely.
Around the same time, turbine fires at six other companies were relative inconveniences. Property damage averaged less than $1 million. Those companies were back in business in less than two weeks.
The difference was proper fire protection. The first group didn’t have it; the second group did.
The power generation industry took notice. Upper-level management began thinking: could the unthinkable happen at our facilities? How would a fire like this affect our overall operations, our bottom line…our market share?
Midlevel managers wanted to know how a turbine lube-oil fire would react in their buildings. Did they have the proper protection, and how long would it take to extinguish such a fire? How much damage would be caused?
Answers were hard to find because no one had ever studied this threat in depth. The most savvy power generation companies knew there was only one way to understand how best to prevent turbine lube-oil fires. Build a mock-up of a turbine hall and set fire to it - something that had never been done before, anywhere. The power generators couldn’t do it themselves, so they turned to a company that could.
“Blaze”-ing a New Trail
It is better to prevent a disaster than to recover from one. This is the premise upon which FM Global was founded in 1835. For more than a century, the company, which insures commercial and industrial properties, has taken its theory and put it into practice.
Today, FM Global employs 1,500 engineers and research scientists worldwide. Its mission is to identify solutions to property hazards related to hurricanes, hail, rain, smoke, fire, electricity and explosions. Much of this work is done at the company’s one-of-a-kind, $78-million, 1,600-acre research campus.
The cornerstone of this unique facility is its large-burn laboratory, a football field-sized testing facility capable of replicating the nastiest of fires. It was at the research campus in early 2004 where FM Global researchers undertook the formidable task of recreating full-scale turbine lube-oil fires.
Researchers first constructed a mock-up of a turbine, turbine pedestal and lube-oil system. One of the key goals for the mock-up was realism. Not only did FM Global want to simulate actual fire conditions as accurately as possible, the company also wanted to be sure the setting would look right to industry experts.
FM Global’s $80,000 mock-up was made of steel. Actual turbine pedestals or foundations are typically concrete. However, FM Global researchers needed their pedestal to be somewhat “portable” to accommodate various tests. The design included high- and intermediate-pressure turbine housings; a foundation pedestal; a grated walkway to simulate an open-floor design; a lube-oil tank and pumping unit; and, a dike surrounding the lube-oil tank.
The pedestal alone measured 15 feet wide, 20 feet long and 18 feet high, with a 7.5-foot grated walkway extending along one edge. To prevent fire from deforming the pedestal during testing, water was pumped through pipes in the pedestal legs.
The next step was to decide which types of fires to test. Three different fire hazards are common in turbine buildings. So, FM Global decided to test all three:
Spray fires. The result of oil being released under high pressure, causing a “spray” effect.
Pool fires. The result of oil accumulating, in depth, on a floor or in a contained area.
Three-dimensional spill fires. The result of oil leaking under low-pressure, cascading from an elevated surface to a lower surface, and igniting along the way.
The final step was to light the fires, and study their behavior. FM Global conducted a total of 23 large-scale fire tests - 10 spray fires, 11 pool fires and two three-dimensional spill fires. Different sprinkler types and configurations were tested as well to determine their effectiveness in combating the fires. The various sprinkler types and configurations tested were:
- Sprinklers with K-factors of 2.8, 5.6, 8.0, 11.2 gpm/psi½ (K-factor is an indication of how much water can be discharged through a sprinkler head at a certain pressure. It is a function of the size and smoothness of the sprinkler nozzle: the smaller the nozzle, the less water that’s discharged at a constant pressure, and the smaller the K-factor … and vice versa.)
- Sprinkler arrangements of 10 feet by 10 feet, 8 feet by 10 feet and 5 feet by 5 feet
- Discharge pressures up to 100 psi
- Sprinkler densities ranging from 0.2 to 3.9 gpm/ft2.
The fuel source was a standard mineral oil with a flash point of 285 F and a 20,000 Btu/lb output. It is important to note that once ignited, this particular lube oil burns like gasoline.
In a very large gas turbine, oil might actually be pumped at levels as high as 800 gpm. For test purposes, however, FM Global pumped the oil at a mere 20 gpm. Even at that relatively low flow rate, the oil produced fires that astonished researchers.
Learning from Burning
The entire facility was dedicated to this test project for more than a month. The turbine lube-oil fire tests produced the most powerful fires ever recorded at FM Global’s new research campus. Some of the spray fires, in particular, generated heat-release-rate bursts of 40 MW. That’s equivalent to the heat caused by a medium-sized house - if it were engulfed in flames.
This past August, FM Global invited more than 100 visitors to witness demonstrations of all three fires and to discover solutions to prevent them. From a safe viewing gallery some 50 feet away, group members were told to place their hands on the windows. Before the first fire was sparked, the group’s tour guide, Dennis Anderson, FM Global’s vice president, told the group to tell him when they started feeling the heat. A few seconds later, the assembled crowd let out a collection of “Whoas,” “Wows” and “Holy cows.”
Among other lessons, the stunned visitors learned that:
- Spray fires and three-dimensional spill fires cannot be extinguished or controlled by ceiling sprinklers.
- Pool fires can be extinguished by ceiling sprinklers, but sprinkler density and ceiling height determine their effectiveness (the greater the distance between sprinkler and flame, the greater the water density needed to put out the fire).
- Local sprinkler protection, such as custom-designed units that provide a water source much closer to the targeted area, can only control these fires.
- Oil flow must be cut off as quickly as possible.
- Lube oil, hydrogen seal oil, control oil and hydraulic fluid present a clear hazard that includes direct heat damage to roofs, cranes, turbines and other building contents.
- A multi-step approach is needed to put out these fires and minimize damage to their facilities.
During spray fires, ceiling temperatures reached nearly 1,500 F without sprinklers turned on and only slightly less than that with just ceiling sprinklers. Temperatures above 1,000 F can lead to steel deformation and, ultimately, roof failure.
Fire testing also showed that sprinklers located on a 5 foot by 5 foot grid with a K factor of 8.0 gpm/psi½ or greater, and discharge pressure of 50 psi or greater, were able to control all fire scenarios when positioned for localized protection (e.g., equipment capable of releasing oil under pressure). This local sprinkler arrangement also reduced gas temperatures at the ceiling from a maximum of 1,500 F to well below 400 F.
One of the biggest surprises occurred during what researchers thought would be a fairly routine pool fire test. When an inadequate amount of water was used, it actually made the pool fire worse. The fire erupted, engulfing the entire turbine platform in a fireball. The heat was so intense it caused several windows in the viewing gallery to crack.
Suffice it to say, the fires served as eye-openers. The individuals who were lucky enough to see the demonstrations in August definitely have a better understanding of the risks posed by these pressurized-oil systems.
The Four Simple Steps
Understanding fire is one thing, but preventing it is another. To prevent a lube oil fire, or at least substantially mitigate the damage it causes, the following four steps are imperative:
1. Safely shut off the oil
2. “Contain and drain”
3. Have an emergency response plan in place
4. Install properly designed sprinkler systems
The good news is that any company can follow the first three rules right now.
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In the event of a turbine lube-oil fire, the oil flow should be terminated as quickly as possible to stop feeding the fire. However, immediately stopping the flow can result in very costly damage to equipment. Therefore, it is important to design shutdown procedures based on site-specific conditions. Proper shutdown could take anywhere from 20 to 45 minutes.
To “contain” an oil leak, shields should be applied at potential oil spray leak points in the lube system and curbing should be installed where necessary to stop the spread of leaking oil. By “draining” leaking oil to a safe containment area, the fire risk is minimized because a potentially volatile fuel source is being removed.
And, of course, emergency response procedures should be in place and all employees should be trained in these procedures.
Experts in fire sprinkler system technology can help companies determine the best way to follow the fourth rule. These four steps, among others (see sidebar), are the most important actions that companies can take to prevent or mitigate the consequences of turbine lube-oil fires. They can mean the difference between a major disaster and a minor distraction.
“Power”-ful Impact
Deregulation of the U.S. power industry has had a profound impact on how utilities view the bottom-line impact of risks such as fire. In the past, power companies had an option for recovering the costs of fire-related damage or loss of service: lobby the state utility commissions to include “purchased power” in the rate base for the period of the outage.
Today, deregulation’s attempt to spur competition has added new business risks to the power industry. As a result, availability of service is now key to a utility’s financial success. Unscheduled downtime is unacceptable.
Ten years ago, few utilities carried time-element (TE) insurance. TE insures against financial losses that add up during the downtime caused by damaged property or equipment. Loss amounts vary depending on how long it takes to repair or replace the damaged goods.
Today, 25 percent of power companies insured by FM Global carry some form of TE coverage. They know TE can be double or triple the value of their property losses in the event of an incident or outage.
Coming Soon…
However, insurance is not enough; prevention is paramount. To prevent other costly catastrophes, new research is in the works. In the coming year, for example, FM Global plans to:
Evaluate less flammable fluids under specific power generation operating conditions.
Study the possibilities of designing active and passive fire protection in the power plants of the future.
Consider new ways to evaluate the useful life left in power transformers.
Examine critical instrumentation and controls, maintenance intervals, central station monitoring of gas turbines, and more.
In the case of turbine lube-oil fire hazards, FM Global helped resolve an issue not only for its clients, but also for the entire power generation industry. The take home lesson in this case is that these fires are potentially devastating to a power company’s bottom line. Fortunately, they’re easily preventable if the four simple steps are followed.
Just think of what your company could do with an extra $410 million.
Author
Terry Cooper is an assistant vice president and power generation industry engineering leader for FM Global, the world’s leading commercial and industrial property insurer. He has 31 years’ experience in the power generation industry working as a consultant for a power generation utility, and with FM Global. Cooper is an active member on several committees of the American Society of Mechanical Engineers (ASME) and is a past chair of the ASME Power Division’s Turbine Generators and Auxiliaries Committee. He has authored several papers, presented at conferences, participated as a panelist and chaired a number of expert panel discussions on power generation issues.
Steps to Preventing Turbine Lube-Oil Fires
Use welded pipe construction wherever possible
Use only flanged and threaded pipe connections. This helps facilitate maintenance at equipment such as bearings, pumps, filters and heat exchangers, and final terminations for instruments.
Consider using stronger, cleaner stainless steel pipe, tubing and fittings instead of carbon steel.
Use guard piping design concepts wherever possible. This allows the supply piping to be incorporated within the return piping.
Insulate against dissimilar material contact at terminations.
Avoid excessive vibrations because they can cause mechanical fatigue and consequent failure of the pressure boundary.
Lock drain valves on reservoirs, storage tanks and conditioning equipment in the closed position.
Prevent released oil from contacting ignition sources by providing proper electrical enclosures and spray shields at flanges to direct the stream away from hot components.
Ensure proper maintenance procedures are followed by using only documented, approved procedures and qualified personnel
Avoid breeching the pressure boundary when the system is in service. For example, only replace filters if isolation is possible and extreme caution is used.
Flush or purge residual oil from the system prior to any hot work.
Ensure vessels are vented to locations that are free of ignition sources.
Consider using checklists to ensure systems that are dismantled for maintenance are properly reinstalled before returning to service.
Consider using a less flammable, FM Approvals approved fluid - a product that meets the stringent demands of FM Approvals, a nationally recognized testing laboratory.
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