5 Feb 2013
A tornado is a narrow, violently rotating column of air that extends from the base of a thunderstorm to the ground. Because wind is invisible, it is hard to see a tornado unless it forms a condensation funnel made up of water droplets, dust and debris. Tornadoes are the most violent of all atmospheric storms.
You might be surprised to learn that more tornadoes hit the United States than any other country in the world. Following up on that, Texas has more tornadoes than any other state. Following up on that, I live in Texas and we have a tornado shelter in the Cottonwood modern project I have been working on.
We didn’t originally design this tornado shelter into the project but after an area not to far from the location of this house was hit by several tornadoes last summer, I received a phone call from the client requesting that we add one to the project. Since the foundation for the house was already poured, the wood floor joists in place, and walls were getting framed into place, my response to his request was “how serious are you about making this a “real” tornado shelter?” Unless you buy pre-made units – like the DuPont™ StormRoom™ with Kevlar® you have to follow certain construction rules – which in our case would have meant ripping out part of the foundation so we could isolate the portion where the tornado room would be built.
The owner elected not to go that far but other than the foundation, he wanted a viable tornado room … let’s call it a “safe” room. It’s a pretty good idea considering that some rooms have a fair amount of floor to ceiling glass walls.
I took these pictures when I was on site in late December – most of what you see in these images has long since been covered up and won’t be as interesting to look at moving forward. This is a modern house but it isn’t so modern that the clients wanted raw plates of steel left exposed. It looks pretty good so I’ll have to remember this for the next “living the dream” loft project I take on. What we have here is a single layer of 14 gauge steel plate sheathing – “minimally attached.”
The room isn’t particularly large – it measures 8′ x 5′ – which is the right size for a closet and for a temporary safe room … just not the right size if you wanted to play the Milton Bradley game of “Twister”
This is the guts of the safe room – double plates with tie downs, elevated floor, lowered ceiling that is not tied to the ceiling framing above … everything that FEMA recommends. Speaking of FEMA, I have include a few of the pages below (click to enlarge) that FEMA developed for the construction of this tornado/safe room. Rather than exhaustively detailing these spaces out in our drawings, we provided the contractor with the appropriate pages and referenced the details.
I am hoping that most – if not all – of the time that the clients will use this room will just be under the “threat” of a tornado rather than an “actual” tornado. As such, we are working to make sure that there is cellular connectivity in this room (a small challenge since the room is shrouded in 14 gauge plate steel) but other than that, this room doesn’t present any challenges to build out. There will be air distributed to the room so it won’t get hot and there is plenty of light (easier to see your playing cards that way). There was conversation at one point about installing a bar in this room but I think the client was kidding … sad to say, but the bar didn’t make the final cut.
Other than not complying with the foundation requirements, the walls and ceilings for this room are rated to withstand a EF-5 tornado (which is the biggest one there is). If you didn’t know, tornadoes are rated on the Enhanced Fujita scale (EF Scale), which rates tornadoes on their intensity based primarily on the damage tornadoes inflict upon man made structures and vegetation. There are 6 levels of tornadoes in the EF Scale system of classification:
EF0 = 65 to 85 mph with a damage path width between 10 to 50 meters (light damage) 38.9% of tornadoes meet this classification
EF1 = 86 to 109 mph with a damage path width between 30 to 150 meters (moderate damage) 35.6% of tornadoes meet this classification
EF2= 110 to 137 mph with a damage path width between 110 to 250 meters (significant damage) 19.4% of tornadoes meet this classification
EF3= 138 to 167 mph with a damage path width between 200 to 500 meters (severe damage) 4.9% of tornadoes meet this classification
EF4= 168 to 199 mph with a damage path width between 400 to 900 meters (devastating damage) 1.1% of tornadoes meet this classification
EF5 = 200 to 234 mph with a damage path width between 1,100 meters and up (incredible damage). Less than 0.1% of tornadoes meet this classification
Some interesting facts about Tornadoes:
- Most Tornadoes occur between 3pm and 9 pm
- Tornadoes can happen anywhere in the world but most are in the United States – an estimated 1,200+ per year (approx 75% or the World’s total)
- The state of Texas gets hit the hardest with an average of 125 tornadoes every year. Oklahoma (57) is second, followed by Florida (55) in third
- Between 60 and 80 people a year die from tornadoes
- The longest path of destruction created by a single tornado was 219 miles. That same tornado was on the ground for approximately 3.5 hours, moved at a ground pace of 73 miles per hour, and was the deadliest tornado on record in the United States – killing 695 people. (The Tri-State Tornado of March 18, 1925)
- The World’s deadliest tornado occurred on April 26, 1989 in The People’s Republic of Bangladesh where a massive tornado took at least 1,300 lives.
- Matt Suter of Fordland, Missouri holds the record for the longest known distance traveled by anyone picked up by a tornado who lived to tell about it. On March 12, 2006 he was carried 1307 feet (398 m), according to National Weather Service measurements.
For more facts about tornadoes, I’d recommend reading through NOAA National Severe Storms Laboratory FAQ page