With the 2005 hurricane season a distinct memory for all involved in those tremendously destructive storms, recovery and reconstruction is a painfully slow process. Rebuilding destroyed homes and businesses within the flood plains and coastal areas requires planning, coupled with foresight and expertise for these buildings to withstand future storms and power loss. This means proper design, location and installation of emergency power systems.
Where buildings are located within an area subject to tornados, hurricanes, ice storms, nor’easters or similar natural disasters, emergency and optional standby power must be located where the power sources will be least affected.
Proper design of the system requires careful consideration about the location of the power source. Is the best location for the power source inside, outside, on the roof or in the basement? The answer to each of these questions is difficult since each type of storm presents its own unique situation.
The topography of the building location plays an important role in determining the ultimate system design. Where a building is located close to the ocean, seawalls or cliffs can provide relative protection for the building and the emergency power source during a Category 3, 4 or 5 storm. These seawalls and cliffs can be added into the design equation and be a major factor in helping ensure water will not cause major inundation of the power source site.
In these situations, the power source can be located closer to ground level. As the danger of seawater intrusion increases due to less natural protection, the power source location should be evaluated and elevated accordingly, based on the projected water level during the storm.
Ensuring proper construction of the building to be able to withstand high wind levels is another major issue for protection of the power source. If the emergency or optional power source is located on the roof and subject to major wind damage during a storm, loss of normal power is then combined with the loss of the backup power, ultimately leaving the building without power, thus negating the design and installation of an alternate power source.
Providing wind shielding for a roof-mounted generator or power unit can be an impossible task where the wind strengths are more than 100 miles per hour. Locating the power source within the building in one of the higher levels can provide the protection required for high wind, but being able to supply fuel may be difficult since the amount of fuel that can be stored within a building is limited by both building and fire codes.
Locating the fuel source external to the building for the emergency or optional power source while preventing the fuel from being contaminated is also a major issue. The type of fuel supplying the power source is dependent on the specific conditions at the site.
Section 700.12(B)(3) requires prime movers for emergency generators, specifically those that are supplied by a public utility gas system or that have a municipal water supply for their cooling system, to have an alternate supply system with automatic switchover. An exception in this section permits the use of other than on-site fuels, but only with permission from the authority having jurisdiction.
This applies where there is a very low probability of simultaneous failure of both the off-site fuel delivery system and the power from the outside electrical utility company.
Having to deliver fuel to the building for the emergency or optional power source from an off-site location may be impossible if the devastation is extensive. Careful choice of fuels and the source of alternate power becomes a major issue.
The topography of the area, the potential for damage, and the type of natural disaster plays heavily in the decisions surrounding the power source and fuel. The choice should be a combination of reliability and the ready availability of the fuel source.
Section 700.9(C) of the 2005 National Electrical Code provides the requirement that emergency wiring circuits must be designed and located so as to minimize the hazards that might cause failure of the emergency system due to flooding, fire, icing, vandalism and other adverse conditions, but leaves the implementation to the designers and installers.
Similar text can be found in the last paragraph in Section 701.11 for legally required standby systems, but is not spelled out in Article 702 covering optional standby systems. Most building owners certainly want similar concerns addressed for the optional systems.
These questions and more will need to be answered as the electrical industry deals with mission-critical buildings and mission-critical functions during natural disasters. EC
ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 or at email@example.com.