Sunday, February 10, 2008

Emergency Back-up Generation Systems for Buildings

The first Primer I wrote on Back-up emergency Generation was in January 2002 right after 9/11/2001. I am often asked why should any building use back-up generation if they are not forced to by local codes? I think 9/11 proved how important back-up generation is to many types of facilities. But remember if you go with back-up generation there are many important points you must consider.

After September 11, 2001 many organizations directly affected by that calamity were shocked to find that their back-up generation did not function. Many systems that did not operate were systems that were never properly tested as normally required. Most code required systems are tested on a weekly basses in accordance with local code requirements.

A few days after September 11, 2001 many facilities were reporting that their backup generation systems were not operative. Studies indicated that the problems were due to many causes. Contaminated fuel, lack of fuel, poor maintenance and lack of testing and poor design were the basic causes of most of the failures.

Of the cases I evaluated several failed due to improper care of long term storage of diesel fuel and natural gas engines failed due to improper gas pressure. One system failed due to the total harmonic distortion exceeding 30% of the total load in trying to operate three elevators. The generator failed and several people became trapped in the buildings elevators. It should be pointed out that this particular installation was only several months old prior to September 11, 2001.

Many facility managers make the big mistake of installing a new generator with out a proper design. They fail to understand what is involved in selecting a generator that can operate all loads including any motors; with out failing do to increased Harmonic Distortion.

In designing any back-up generator system for a commercial and Industrial building the designer must understand the purpose of the back-up system. The majority of such systems installed are normally legally required emergency generator back up systems. Such systems are primarily utilized for short duration power outages caused by a variety of power interrupting occurrences that are considered non standard as related to the reliability of the power utility system.

These short duration power disruptions are normally in the magnitude of minutes to many minutes but not normally exceeding 2 hours. For this reason most life safety codes require the system to be able to stay on line for back up purposes at least 2 hours. If the owner desires a system that will stay activated for longer than two hours than the designer must coordinate this requirement carefully with the owner so they are aware of the increase in cost that can result from designing a system for longer durations.

When power disruptions are caused by disasters it is essential that the power from back-up generation not be activated until a complete damage assessment is completed. Deaths have occurred after disasters have passed due to electrocution caused by the power restored by back-up generation before a complete building damage assessment is done and before damage is repaired. Fires, grounding problems and back feeding caused by back up generation is known to have occurred because of faulty damage repairs or the lack of proper repairs. NEVER activate your back-up generation system after a disaster with out first doing a complete damage assessment.

For more detailed information please see my book "Emergency Back-up Generation - Design, Operation, Maintenance, and Failures" available at