Few people think much about generator noise until they find themselves exposed to it, usually unexpectedly and often for sustained periods of time. When disaster strikes, a power outage can be catastrophic for companies and organizations dependent on computer systems to remain operational, and they turn to generators to maintain critical systems and operations.
In the latter weeks of April, 2011 a rash of devastating storms in the Southeast U.S. left 1.1 million businesses and homes (and one nuclear power plant) without power when high winds knocked down dozens of high-voltage transmission lines in northern Alabama and Mississippi, leaving residents and businesses dependent on emergency generators for weeks.
With the number of power outages caused by destructive weather systems alone on the rise, the use of stand-by and emergency generators has risen significantly. For homeowners and corporate organizations, these generators are a necessity for providing power to refrigerate food, cool or heat a home, and keep computer systems operational until power is restored.
But along with generators comes noise, often at decibel levels of 100 and higher. In areas where more than one generator is operating, such as in a disaster area where there can easily be a cacaphony of generator noise pervading an entire community, the noise can lead to health problems among individuals exposed to it for more than brief periods of time.
Generator noise comes from two sources: Mechanical noise from moving parts, and combustion noise from the engine. Noise from emergency generators can easily exceed 100 decibels, which translates to the noise of a jack hammer at 10 meters (32.8 feet); 110dB is the noise equivalent of a plane taking off at a 10 meters; 115 dB translates to a jet’s screeching whistle at 10 meters, and is also the threshold of noise-induced pain. Sustained noise levels above this can cause hearing damage in short a short amount of time. Sustained noise at 100 dB can cause long term health problems.
Obviously, the more generators in operation at one time, the louder the noise level. Sound barriers (of sufficient height & material) can make a substantial difference in the noise exposure levels from generators. To be effective, a noise barrier fence or structure must at least block the line-of-sight from the source to the receiver. When dealing with generator noise, it is important to take into account the source height of the generator, which can be fairly high, and to consider the height of the receiver if the impacted site has multiple floors.
When generator noise is already causing a problem, or to predict the impact, help determine compliance with the relevant noise codes, or to help control the impact of generator noise, seek the advice of an acoustical professional to assess the particulars of your specific project.
Stand-by generators are typically tested for 1-4 hours 1-2 times per month. Although no one can predict when a power outage will occur, the testing can be scheduled during a non-sensitive time and day. If scheduling tests can not be managed for times when others can avoid exposure, temporary and permanent noise deadening options are available.