Risk at 96 Hours until Landfall

Table 5.5 shows the probability of obtaining each damage state from the example storm, as well as the resultant risk from each damage state. The addition of a second story influences the contribution of roof damage to the overall structural damage. Because of the presence of an intermediate barrier (the second story‟s floor decking), roofing damage does not correlate as directly to damage on the bottom floor. This correlation would be even weaker with the addition of more stories.

Table 5.5 Wind Risk at 96 Hours Until Landfall

Damage State Risk Habitable P (%) Resultant Risk Habitable

1 - Minor Damage Low Yes 65.4 Low Yes

2 - Moderate Damage Low Yes 49.0 Low Yes

3 - Severe Damage Medium No 30.2 Medium No

4 - Destruction High No 0.2 Low Yes

5.4.1 Effect of Individual Wind Damage States

From the previous analysis, there is a 65.4% probability of experiencing at least Damage State 1. This damage state is defined as up to 15 percent roof cover loss, the loss of 1 window or door, and less than 5 missile impacts. Based on this, the risk to residents in the structure would be minimal, and the structure would be habitable after the storm.

There is a 49% probability of experiencing at least Damage State 2. This is defined as up to 50 percent roof cover loss, 2% window/door failures, 1 – 2 roof panels lost, and 5 – 10 missile impacts. Based on this information, the risk to residents in the structure would still be minimal if

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the following conditions were met: areas exposed to windows and doors susceptible to failure could not be used as well as areas on the second floor where roof panels could be lost. These areas would most likely be at edges and corners where wind pressures are the highest. After the storm, the structure would still be habitable as long as damaged areas were covered to prevent additional water from entering the structure.

There is a 30.2% probability of experiencing at least Damage State 3. This Damage State is defined as greater than 50 percent roof cover loss, up to 25 percent window loss, up to 25 percent roof deck loss, 10 – 20 missile impacts, and up to 25 percent roof joists failure. This damage state poses greater risks to inhabitants of the structure. The second flood could not be used as shelter, and outer areas of the first flood with windows susceptible to failure could not be used. Risk to residents in the structure would be medium. Based on this damage state, the

structure would not be habitable after the storm due to water intrusion, and significant repairs would be needed before the structure could be occupied again.

Damage State 4 had 0.2% probability of occurring. This damage state has a high

consequence if it occurs. Damage State 4 is defined as greater than 25% roof deck and window failure. Additionally, >25% of roof joist are expected to fail. This level of failure severely compromises the structure. The structure could not be used as a shelter and would need

significant repairs after the storm before it could be habitable. It is not expected that this damage state will occur.

5.4.2 Flood Analysis

From the rainfall flood analysis, 0.5 feet of flooding at the site could reasonably be expected. This flooding is only an estimate as rainfall is difficult to forecast, especially at long ranges. For 0.5 feet of flooding, there is minimal risk to life safety. Habitants exposed to this level of flooding would be at minimal risk for drowning, and there is not enough depth for

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structural integrity to be affected. However, this level of flooding does affect the habitability of the structure. Any level of flooding can affect building systems (electrical, plumbing, etc) and make the structure unusable.

The surge analysis revealed significant potential hazard to occupants of the structure. Enough potential depth existed to be a direct threat to life safety as well as a secondary threat by affecting the buildings structural integrity. The SLOSH MEOW flood values are maximums, and likely are a conservative estimate of flooding. Actual surge flooding may differ significantly. However, the surge flooding is a potential hazard, as was the rainfall flooding. Surge flooding is geographically sensitive and small changes in hurricane track can cause large changes in storm surge height.

5.4.3 Evacuation Risks

While there are risks from hurricane hazards which must be considered, there are also specific risks from evacuation. The first such risk is the risk from traffic fatalities. Nationally, the average number of traffic fatalities is 1.41 fatalities for every 100 million vehicle miles traveled. Based on the comparatively short distance being traveled (evacuations are typically not further than a few hundred miles), and the relatively low number of vehicles needed, the risk of traffic fatalities would be low. Although the risk is low, the consequence of a traffic accident is high, especially if buses are being used. An example of this occurred during the Hurricane Rita evacuation, where a bus fire South of Dallas claimed the lives of 24 nursing home patients being evacuated from Houston (Zachria 2006).

The risk to building residents health must also be taken into consideration. For critical care residents, such as some of those in hospitals and nursing homes, being evacuated can result in fatalities. While there is no specific method available to quantify this risk, anecdotal data suggest that the bulk of casualties in hurricane evacuations are from critical care portions of the

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population as discussed in Section 2.9. The specific risk to individual residents also depends on their condition and the resources available to the facility.