Safety upgrades are always on the agenda when a hydropower plant undergoes a rewind. With the extended downtime of a longer outage, owners can review potential safety risks to determine if advances in technology have led to solutions that were not previously available. One of the most obvious worker safety risks is the widely used CO2 fire suppression system, which can cause worker injury and death in the event of a system discharge. Since removal and reinstallation of the CO2 system is required during a rewind, it is a prime opportunity for upgrading to a safer solution.
Understanding the status quo
Choosing a fire protection system for hydropower generator enclosures historically has been a decision plagued by compromises. When many of today’s plants were built, halon systems were commonplace. While halon was effective at suppressing fires, exposure was known to cause negative health effects, and because of its harmful environmental impact, production of halon was banned by the United States Environmental Protection Agency in 1998.
For these reasons, many facilities have replaced halon systems with CO2 fire suppression systems. The advantages of CO2 systems are the way it suppresses a fire by reducing the oxygen concentration level in the protected area to a point that inhibits combustion and the minimal cleanup and downtime required after a discharge. Unfortunately, however, CO2 systems can be lethal for humans caught in the protected area during a false discharge or an active fire event.
Stepping beyond standard designs
An advanced hybrid fire extinguishing system can eliminate safety hazards without sacrificing effectiveness. The Victaulic Vortex™ system uses water droplets smaller than white blood cells and nitrogen, a naturally occurring gas, discharged from a single emitter to absorb heat and reduce oxygen to a volumetric-calculated target to extinguish a fire.
The system consists of releasing panels, stored nitrogen, a captive water supply, low-pressure distribution piping and emitters in the hazard area. It is fully compatible with hazard detection systems like heat, smoke, and air sampling, and most importantly, the design can be integrated easily in older facilities using existing SCADA and fire control panels.
Near miss drives change
Following a recent CO2 discharge that could have exposed workers to dangerous conditions, a hydropower facility owner began evaluating non-lethal fire suppression systems that could be installed in several plants. In addition to being innocuous for people, the system would need to be effective for various hazards, safe in areas with energized generators, easy to install, and simple to maintain.
Testing and validation proved that Victaulic’s hybrid fire extinguishing system checked all the boxes. It is scalable, creates no damaging conditions for equipment, can be installed in existing facilities without the need for significant reconstruction, and is easy to service. The successful installation of the hybrid system proved its efficacy and led to the owner’s decision to use it in additional hydropower facilities.
Installing the system
Dedicated in 1967, Boundary Dam, on the Pend Oreille River in northeastern Washington, is the second tallest arch dam in Washington State, and its underground powerhouse is one of the largest in the country. The unique design of the dam places the powerhouse and offices inside the mountain. Workers enter and exit through a 500-ft tunnel, a design element that posed challenges for the CO2 fire suppression system, which required workers to evacuate before it could be deployed. Delaying activation of the fire suppression system presented life safety issues for workers along with the possibility of significant damage to the facility if fire spread unchecked while workers were removed from harm’s way.
Seattle City Light, the plant owner, decided to install a hybrid fire extinguishing system based on its safety advantages, minimal water usage, and easy cleanup
Fire Protection Specialists, LLC (FirePro) of Spokane, Washington, was awarded the contract to integrate the hybrid fire extinguishing system into the generator housing. Workers removed the existing CO2 system and began reviewing the as-built drawings, visiting the site to get an understanding of the current pipe pathways before designing the control system layout for the new installation.
According to FirePro Senior Project Manager Chris Burnett, there are challenges in placing a system inside a generator because of the unit’s shape. “Generator rooms typically are round, which means there are a lot of angles and tight spaces. Being able to use the same pathways is critical because it simplifies installation,” he said.
Retrofit projects require a high level of coordination between the customer and the integrator. “Every action we take in a facility is determined cooperatively with the customer,” Burnett said. “We use a very detailed schematic that is integrated into the plant blueprint so as-built drawings are consistent because we need to know where every single wire lands, what it does, and where the pathway is.”
Seattle City Light informed FirePro of where it was possible to run lines, where pathways were less ideal because of threats or concerns, and where running a line was prohibited for safety reasons, for example, in high-voltage areas.
With the schematic plans ready, the next step was to figure out where new equipment could be placed in a powerhouse with limited real estate so it could be accessed and serviced easily. Once this was determined, FirePro needed to familiarize its crew with the facility’s requirements for installing the system inside the generator, where loose components could result in serious damage. “Every facility has its own method for securing bolts – special kinds of washers, safety measures, or even wire ties – to prevent things from coming loose and affecting generator functionality,” he said.
Enhancing safety
“Intelligent detection and extinguishment are big improvements over the conventional detection and suppression system,” Burnett said, explaining, “The old system would not be able to detect a problem as it was developing. It could only record a suppression system discharge.”
A hybrid fire extinguishing system paired with air sampling detection can identify even low levels of smoke and other impurities, which allows for real-time hazard identification and precise control of system discharges. An air sampler tests the environment and sends information about what has been detected to the fire control panel in the central control room, informing the operator of potential problems that might require further investigation.
A special feature of the system installed at Boundary Dam is the custom graphic annunciators, created specifically to provide a visual indicator in addition to the audible alarm when there is any activity on the system. “If a valve is shut, a light in the control room lets the safety crew see in real time that something is happening,” Burnett said.
Connecting the new detection and hybrid fire extinguishing control system with existing relays and signaling for such things as generator shutdown and annunciation could have been complicated, but according to Burnett, tying in the hybrid system was straightforward.
“The beautiful thing about the system is that it can integrate with any detection system – old, new, or mix of both,” he said.
Putting the system to the test
According to Burnett, experience gained during its first hybrid fire safety system installation for Seattle City Light allowed FirePro to make improvements during the testing of the Boundary Dam system. For example, learnings from the discharge test at Diablo Dam a year earlier led to the decision to install O2 sensors inside air housings and temperature probes throughout the space for optimal coverage and improved measurement.
One of most important performance criteria dictated by the owner was that the system only discharge after the generator dropped under 500 volts to further safeguard against concerns related to unwanted conductivity. To meet this demand, the system installed at Boundary Dam delays the discharge for 30 seconds after discharge criteria were met to allow wind-down time to drop below 500 volts.”
For the system test, a viewing station was set up with multiple monitors receiving live video from five cameras positioned at the generator. Observers could see the emitters and O2 sensors within and outside of the generator. The test measured results in the protected hazard area, as well as outside the space, to verify that there was minimal leakage to the outside environment.
FirePro initiated a full discharge test immediately after shutoff under worst-case conditions. Seattle City Light hoped to see the oxygen level reduced to where combustion could not be sustained during the discharge test and the system held the oxygen concentration level at 12.5% to 13.5% for 45 minutes with the door to the unit open.
Effective installations
The integration of the Victaulic Vortex™ fire extinguishing system in multiple hydropower facilities proves the system can be retrofitted effectively in aging units. Owners that are weighing fire suppression system replacement options during upgrades now have many reasons for considering a hybrid system. System installations can be carried out quickly, and once installed hybrid fire extinguishing systems provide peace of mind for personnel safety during activation with a non-toxic hybrid media and controlled discharge rates, have no need for assurance of tight room integrity, and no costly clean up or equipment replacement.
