Tornadoes and Other High Winds

It goes without saying that  Data Center clients are always looking to locate in an area that fits certain favorable criteria for data centers, not the least of which is a lack of major weather events that might contribute to downtime.  If you look on the SuperNAP website, they are very proud of the fact that they are located in a zone of the country that has virtually no disruptive weather events (Las Vegas).  There is little rain, no hurricanes, earthquakes, volcanoes or few tornadoes.  Of course, weather can’t be the only deciding factor, others might include tax incentives or the cost of utilities, or proximity or connectivity to regional or national locales.  For all the clients that cannot locate their entire IT operation in Las Vegas, weather events will eventually come up as part of the risk assessment.

I am by no means an expert on chance, nor am I an insurance adjuster, but it is still an interesting exercise to watch.  If you have ever played roulette, you have probably seen the sign above the wheel that shows the results of the last few spins.  It should be obvious to all of us that it is purely a game of chance, and that the numbers on the sign are not an indicator that a certain number or color is due because it keeps showing up or doesn’t show up at all.  If the last three spins were 18, then the odds that the next spin will be 18 will still be one in 38 (on an American wheel, for you gambling enthusiasts).  So it is with tornadoes.  We look at historical data, and to some degree we can say with certainty that particular areas of the country will receive more tornadoes than others.  Beyond that, it gets a little fuzzier, and this stems from an evolving process for studying and understanding tornadoes.

The currently accepted measure of severity for tornadoes is the Enhanced Fujita Scale, based on research from the National Weather Service, American Meteorological Society and the Wind Science and Engineering Research Center at Texas Tech.  With time and more exhaustive research, this scale will become more accurate and useful, however, I see two major issues with the scale as it exists currently.  First, the scale is based on observed damage, not on direct measurement of a tornado event.  This means that they look at the damage, and then try to figure out what kind of wind would be required to cause that much damage.  Second, our records of tornado events are incomplete and inconsistent earlier than 1950, when these events were tracked in a national registry.

I’ll address the windspeed first.  The windspeed factor is crucial because this is the end result that we are trying to understand.  When we design a data center, the windspeed which it should resist is among the first decisions made.  We look at the frequency of tornadoes of all scales and pick a design wind speed in excess of that which is required by local building code.  The danger here is that, since the Fujita scale is based on observed damage, it is conceivable that an owner either over builds and thus wastes resources that could have gone into critical infrastructure, or underestimates the risk, exposing the facility to more risk than was assumed based on historical data.

And this brings up the second issue which is historical data.  Consider this:  America is a large country, and is not densely populated from coast to coast, there are gaps between population centers.  If a tornado were to strike one of these areas and not cause any noted damage, would there be damage to assess a windspeed, or would the tornado even be registered?  I suspect that the recorded data probably under-counts the number of tornadoes in a given state or county.  The other question is how accurate past accounts of damage were when being assessed on the Fujita scale.

Ultimately, the decision rests with the owner.  Just like with investments, past performance is no guarantee of future returns, and the decision will come down the owner’s tolerance for risk at that facility.  I have heard of people locating in bunkers, and others who take a riskier approach per facility by distributing processes.


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