Ensuring emergency power after a natural disaster

Could a Fukushima-type disaster happen here?


Figure 1: This map shows the average number of tornadoes annually. Courtesy: National Oceanic and Atmospheric Administration (NOAA). Courtesy: Seismic Source InternationalIn March 2011, a 9.0 earthquake followed by a tsunami shocked Japan's northern shore. The devastation to four nuclear reactors in Fukushima caused a state of emergency. The on-site power generators at the plant survived the shake only to be disabled by the tsunami. With no backup power, the cooling pumps could not operate, and without power, the ability to cool the core was disabled, which led to core meltdown. In 2012, Hurricane Sandy hit the northeastern seaboard, crippling emergency power as wind and flooding knocked out many on-site power systems for critical facilities. How prepared are we to maintain emergency power in the wake of natural disasters, such as earthquakes, wind, and floods? Can we limit our vulnerability?

Extreme, but not uncommon
It can be easy to be lulled into a false sense of comfort that "extreme" equals "uncommon." But natural events are fairly common with a number of devastating natural disasters occurring in recent years.

Earthquakes: Worldwide, there is an average of 100 earthquakes per year resulting in damage. In 2013, there were two 7.0 to 7.9 earthquakes in the U.S. and three 6.0 to 6.9. In 2012, there were five 6.0 to 6.9 and 27 that were 5.0 to 5.9. West Virginia experienced a 5.8 in August 2011 that was felt in a dozen states, damaging the Washington Monument and the National Cathedral in Washington D.C., and triggering a shutdown of two reactors at the North Anna nuclear power plant near Mineral, Va. Fortunately, the plant's four emergency diesel generators started and supplied power to important electrical equipment while off-site power was down. On Jan. 12, 2010, a 7.0 earthquake hit Haiti, leveling much of Port-au-Prince. On Feb. 27, 2010, an 8.8 in Chile toppled entire buildings. The city of Christchurch, New Zealand, was rocked by a 7.0 in late 2010 followed by a targeted 6.3 in February 2011 that destroyed hundreds of buildings. The 1994 Northridge earthquake near Los Angeles, Calif., caused nearly $80 billion in damage. Power outages were experienced as far as British Columbia, Montana, Idaho, Oregon, Washington, and Wyoming-in some cases for up to three days, and intermittently up to a week (see "Earthquake states, statistics").

Wind: High winds from hurricanes, tornadoes, nor'easters, and severe storms affect emergency power every year. Approximately 10,000 severe thunderstorms and more than 1,000 tornadoes occur each year in the U.S.-more than any other country (see Figure 1). There have been an average of 33 killer tornadoes per year between 2011 and 2014. The busiest calendar day for tornadoes was April 27, 2011 (see Figure 2). Millions of customers had power knocked out, including three county emergency operation centers and a 911 dispatch center in Alabama. Some areas took more than a week to restore power. Joplin, Mo., was devastated by the worst tornado since 1947 with more than 150 fatalities and $2.8 billion in damage. In 2004, there were 1,817 tornadoes-a new record. An average of 17 hurricanes per decade have hit the U.S. In 2013, there were 13 named tropical storms in the Atlantic and 18 in the Pacific-11 of these storms developed into hurricanes. Hurricanes Sandy in 2012, Ike in 2008, and Katrina in 2005 were the costliest in damage to date in the U.S. In 2005, there were 27 named storms, 15 of which became hurricanes (see Table 1).

Figure 2: The busiest calendar day for tornadoes was April 27, 2011. This map shows where they occurred. Courtesy: National Oceanic and Atmospheric Administration (NOAA). Courtesy: Seismic Source InternationalFloods: Floods are the most common disaster in the U.S. More than 70% of presidential disaster declarations are for flooding. Floods are caused by riverine flooding, resulting from overflow of rivers, waterways, dams, etc. when rainfall or snowmelt exceeds their capacity. They are also caused by coastal flooding due to storm surges caused by hurricanes, tropical storms, nor'easters, and tsunamis. In 2011, the Missouri River experienced widespread flooding due to snow melt and rain. Fort Calhoun nuclear power station near Blair, Neb., had to install temporary levees to protect financial assets. Portable fuel trucks were installed at a height above the flood plane to ensure availability of fuel if there was a loss of offsite power. Flood surges in Hurricanes Sandy, Ike, and Katrina severely affected emergency power. During 2008, record precipitation, coupled with already saturated soils, resulted in flooding along many rivers in the U.S. Midwest. Flooding events occurred from January to September of 2008. Substantial record flooding and damage occurred in Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, Oklahoma, South Dakota, and Wisconsin. During 2008, peak-of-record stream flows were recorded at more than 147 U.S. Geological Survey (USGS) stream gages. Emergency generators at several law enforcement agencies were destroyed by floodwaters. Figure 3 shows a USGS map of stream gage measurements across the U.S. from 2008 to 2013.

There is no shortage of natural disasters. All 50 states experience some sort of natural disaster that knocks out daily utility power. Facilities, especially critical facilities that are essential to provide necessary services after a disaster, must keep on-site backup power available to continue operation in the absence of utility power. It is crucial to design and install on-site emergency power systems to survive these disasters.

Emergency power vulnerabilities
Earthquakes, wind, and floods are the forces of nature responsible for challenging the vulnerabilities of emergency and backup power systems. However, taking the appropriate precautions can help guard against these vulnerabilities.

Earthquakes: During an earthquake, the ground motion creates a dynamic response in a building and its equipment. This interaction creates an acceleration applied to equipment that results in a sometimes violent shaking. This effect can increase up to a factor of three for equipment mounted on the roof. Emergency generator systems must be capable of withstanding imposed seismic loads. They must be sufficiently anchored to resist seismic loads with no parts becoming detached from the building. They must also accommodate differential movement between the equipment and connected systems, such as exhaust systems, fuel lines, wiring, and process pipes such as coolant.

Figure 3: This USGS map shows the locations of stream gages across the U.S. Courtesy: U.S. Geological Survey (USGS) WaterWatch. Courtesy: Seismic Source International Emergency generators that are properly anchored typically perform well. However, common failures experienced in recent earthquakes include:

  • Off-site natural gas fuel supply was interrupted
  • Generator failed to operate due to component damage
  • Anchors missing
  • Battery backups not anchored
  • Fuel tank not anchored
  • Exhaust stack not braced
  • Fuel oil pipe not braced
  • Failure of isolator supports that were not seismically rated or anchored
  • Lack of flex connectors between the unit and distribution systems.

For emergency power to function, interconnected systems require attention too. This includes ancillary equipment such as starters, fuel and lubrication pumps, cooling equipment, and more. Distribution systems, such as switchgear, panels, controllers, feeders, branch circuits, transfer switches, transformers, and so on, need to function. Failure of any component in the emergency power system can prevent its operation. All components of the system must be braced for seismic loads.

Table 1: Costliest U.S. hurricanesWind:
Damage to on-site power generating equipment by wind forces has increased concern about the adequacy of equipment protection. Wind effects must be evaluated for two main areas of the power generating equipment: the equipment that is exposed to wind and the exterior wall-mounted cladding components, such as intake and exhaust louvers. Protection from wind-borne missiles (debris) is a design consideration but not a code issue. The barriers that protect the power generating equipment can be designed for missiles. Louvers that need to operate are especially vulnerable. Exhaust stacks and any part of the equipment that may be unprotected should be part of the design considerations. Generally, on-site power equipment resists wind well if anchored properly. However, some vulnerabilities to wind include:

  • No on-site emergency power; if no emergency power is in place, critical facilities can offer only limited or no service
  • Not anchored properly
  • Fuel tank not anchored properly
  • Remote radiator not anchored properly
  • Enclosure or louvers not capable of wind loads
  • Exhaust muffler not anchored properly for wind load. 

Floods: Flood damage poses one of the greatest risks to on-site power. The most common reason for flood-damaged emergency generators is location. Mechanical and electrical equipment is often located in lower levels of a building. The lowest level of the building is also the most likely to flood. Floodwater can damage or inundate fuel tanks that supply diesel generators, damage fuel oil pumping equipment, and knock out emergency power distribution equipment, such as transfer switches, panels, and feeders. After Hurricane Katrina, generators in a hospital were elevated but the transfer switches were not. The switches were rendered inoperable by flooding. Although the generators could function, there was no way to transfer the power to critical equipment. Many of a major medical campus's emergency generators were located in lower levels and flooded during Hurricane Ike. These buildings could not provide many critical services. In one building, the generator and associated equipment were mounted on the second floor. High and dry, they remained operable during and after the flood.

Similar issues rendered emergency power in critical facilities useless during the 2008 Midwest floods. In one instance, bucket brigades formed a line up 14 flights of stairs to carry diesel fuel to the generators. The fuel pumps had been located on a lower level and were destroyed by floodwaters. Fuel supply is an important design consideration for emergency power equipment. Both above ground and buried tanks have additional flooding concerns that need to be addressed. Buried tanks need to be evaluated for the additional hydrostatic pressure of the water levels above grade. Aboveground tanks must be anchored and elevated so they are not swept away by moving water. The anchors also restrain the tank as the fuel is used where the void will cause a buoyancy uplift. Both aboveground and buried tanks need to be evaluated for the flood level and operation. The weight of the water could cause a failure of a buried tank from the hydrostatic load. If the floodwater is going to stay for an extended period of time, refueling is an issue. All tanks are vented, so the vent pipe must be extended above the potential flood levels.

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