By Jeffery H. Warren, Ph.D., P.E., CSP
In hurricane situations, wind or water or both may cause damage. Determining the cause of the damage is critical in the claim settlement. Specific information about the storm will be very helpful in making this determination.
Knowing the power of wind compared to the power of water can help in assessing damages. Wind is less destructive than a storm surge. For example, wind at 40 mph produces 7 pounds of pressure per square foot (psf) compared to a wave at 7mph produces 200 pounds of pressure per square foot (psf). There is zero wind velocity at the ground level therefore, wind forces increase exponentially with height above the ground. Winds passing over and around a building can develop negative or "pulling" pressure in addition to the "pushing" pressure. The average wooden roof is designed to sustain 30 psf, which means 80 mph winds are needed to cause considerable damage.
Storm surge is the combination of wind and low atmospheric pressure. It can range from 3-4 feet to 15 -20 feet. Keep in mind 1 inch of falling barometric pressure is going to raise the water level about 1 foot. Although it is hard to imagine how strong water can be, remember a cubic yard of water (3ft x 3ft x 3ft) weighs over ¾ ton. A breaking wave is so deadly because of this intense power. A modest 4-foot wave striking an 8-10 foot wall could destroy it. Obviously, this is the reason building codes require structures to be built above the wave height which is the best way to mitigate a loss.
Wind speeds and storm surge is not the only thing to be concerned about when it comes to hurricanes. In the last 30 years, more people have died from inland flooding than from tidal surges. Intense rainfall is not related to wind speed. The greatest rainfall amounts often occur from weaker storms that drift slowly or stall over an area. Last year, Hurricane Floyd brought intense rains and record flooding. Of the 56 lives lost during this storm, 50 drowned due to inland flooding. Machinery, heavy equipment and vehicles often sustain significant damage from flooding. Flood Damaged Machinery and Repair Guideline #200 and #300 will assist you and your insured in assessing and mitigating flood damage.
Extensive investigation and documentation work must be done to determine the cause of the loss. Please refer to the Wind & Water Investigation Tips to assist you in analyzing hurricane losses. When a hurricane occurs, many issues must be addressed to understand the loss. Engineers at The Warren Group have experience with these losses and are happy to consult with you.
