BY DON KIRKHAM
A reliable fire station emergency power supply is essential during power outages. Although a station’s backup generator may be tested frequently, such testing is often done at a level well below the power unit’s maximum capacity, which could result in wet stacking. This phenomenon could eventually damage the generator’s components, with disastrous results when the emergency generator is actually needed.
In routine testing, since the emergency generator does not usually reach its ideal operating temperature, it may not burn the fuel completely. When unburned fuel is allowed to migrate back into the cylinders, it diminishes the lubricating qualities of the oil and eventually causes premature wear of the cylinder wall. Eventually, the unburned fuel will dilute the engine oil and may cause the engine bearings to fail.
Wet stacking, according to National Fire Protection Association (NFPA) 110, Standard on Emergency and Standby Power Systems—1996, Section 6-4.2, is a field term that describes the presence of unburned fuel or carbon in the exhaust system. Its presence is readily indicated by black smoke during engine-run operations. The 1999 edition suggests using a more quantitative methodology that in-volves measuring exhaust gas temperature.
PLANNING UNIT CAPACITY AND TESTING
Diesel engine wet stacking can figure in planning a new fire station or remodeling an existing one. Imagine that the planning committee decides to design every piece of equipment and electrical receptacle such that it can function on backup power under power outage conditions. This is a great strategy, except that since the unit is exercised weekly or monthly under a load that is below 30 percent of its capacity, it does not operate efficiently, which can lead to wet stacking. Planning for the electrical standby power requirements involves an in-depth study of the facility’s resistive and inductive load, which includes examining the electrical motor efficiency ratings for such systems as HVAC, air compressors, and so forth. This in-depth study can be relatively quick and painless. Kohler Co. has a Web site that allows users to size emergency power units according to their particular requirements (www.kohlerpowersystems.com).
NFPA AND JCAHO GUIDELINES
According to NFPA 110, Section 8.4.2* guidelines in Level 1 and 2 applications, power units are to be exercised at least monthly for 30 minutes under one of the two following criteria:
(1) Under operating temperature conditions and at not less than 30 percent of the EPS nameplate kW rating.
(2) Loading that maintains the minimum exhaust gas temperatures as recommended by the manufacturer.
The power unit’s manufacturer provides the exhaust gas temperature specifications.
The Joint Committee on Accreditation of Healthcare Organizations (JCAHO), which accredits health care institutions, has taken this testing to a level beyond that of the NFPA. According to the JCAHO EC 2.14 revised standard, organizations are required to test the generator systems 12 times per year with testing intervals between 20 and 40 days. Generators must be tested for at least 30 minutes under a dynamic load of at least 30 percent or greater of the nameplate rating. Organizations with systems that do not meet the 30-percent load capacity have three options:
1. Increase the load to the generator to meet or exceed 30 percent of the nameplate capacity.
2. Obtain correct operating temperature conditions from manufacturers, and maintain the minimum exhaust temperature.
3. Load bank consists of the following annual exercise:
—Loads at 25 percent of nameplate for 30 minutes, followed by
—Loads at 50 percent of nameplate for 30 minutes, followed by
—Loads at 75 percent of nameplate for 60 minutes for a total of 2 continuous hours.
The standard continues, “All automatic transfer switches (ATS) also must be tested 12 times per year, with intervals of between 20 and 40 days. It is important to ensure that engineers and other appropriate staff are trained in procedures to follow when automatic transfer switches fail.” (From Healthsafetyinfo.com Web site, www.healthsafetyinfo.com/articles/gen_test.cfm.)
ARTIFICIAL LOAD BANKS
In designing a new fire station, planning for and sizing a backup power unit is critical for its successful operation. The backup unit should have the capacity to power every electrical device in a fire station, although the normal connected load may only be 25 percent of the unit’s capacity. How do we solve the wet stacking problem?
During the station planning stages, consider installing an artificial load bank and testing at weekly or monthly intervals. Alternatively, a portable artificial load bank should be brought in to test the backup generator unit at least annually or at more frequent intervals if possible. An artificial electrical load bank develops electrical loads, draws power from a source, and dissipates the resultant power. In short, it increases the load on the generator and then dissipates that energy. Exercising the generator with a heavier load than it would usually experience but might experience during a power outage is beneficial for the unit. Artificial load banks are inexpensive when you consider the alternatives. Enlisting a qualified professional to discuss these issues is essential at the outset.
INSPECTIONS
Fire inspectors may have the opportunity to witness an annual fire pump test backed up with a diesel-powered generator for the pump’s electrical supply. Understanding the dynamics of wet stacking and its ramifications on the critical fire pump system is essential. Knowing the inherent problems associated with each component of the fire pump system is the responsibility of the inspector.
Preplanning for a new station or remodeling an existing one is a daunting task for anyone. Knowing the long-term maintenance issues for each system of your new station is critical for its productive and efficient use. Inspectors are inundated with a myriad of complex systems to understand and inspect. These include manual and automatic transfer switches, uninterruptible power supply (UPS) systems, and other components. The correct maintenance of an emergency or standby power system is an area of concern for our customers. Offering clear, concise information about a complex subject is the duty of a well-informed fire official.
DON KIRKHAM is a retired firefighter/medic from the Delaware City (OH) Fire Department. He has a bachelor of science degree in fire science and engineering, a master’s degree in public administration, and a Ph.D. in business administration. Kirkham is facility manager for Velocys, a research and development company, and has been the construction project manager for Ohio University’s newest satellite campus in Pickerington, Ohio.
