Just perusing through glocktalk.com, found that they've added a survival and preparedness forum. One of the forum stickies is this long list of tornado shelters.

http://glocktalk.com/forums/showthread.php?t=623076

interesting

I've always wondered of these things would survive the funnel of the tornado going across them.

Anyone?

From what I understand there's not a lot of turbulence at the extreme tip of a tornado...it's sort of like the eye of a hurricane. The last hurricane that came through here was a long time ago but when it did I remember reading about houses that were completely shredded but the basements were still intact with books still on bookshelves and very little disturbed.

Even if that's completely wrong these things look HEAVY and they're completely buried.

Hey ... I'm an anyone.

I understand that these types of units are intended to be buried so that only the hatch at the top is exposed. And it only to vertical forces. Put something mostly underground and you gain quite a bit on surviving a tornado. Laying in a ditch or climbing into a culvert are classic ways to survive a tornado. this looks to be an up-scale and modernized version of the old farmers standby, the root cellar.

Good protection because it is pretty hard to break dirt.

Leigh,

It's not likely the direct passage of the funnel over these shelters would pull them out of the ground. The lateral pressure of the tornado is what causes the debris field to be created. Since these shelters are buried the surface area exposed to the wind is relatively small. My only suggestion if someone was to install one of these would be to have a hydraulic jack of considerable strength and some 4X4 lumber stowed in the shelter. If the debris from the tornado is piled up on the door there is every possibility that you may not be able to open the door. The jack and lumber would allow egress.

My thoughts...

As I understand it: The air pressure in the funnel is a lot lower than on the outside. Not zero pressure but low enough to kill. So what happens if the tornando bullseye's the hatch?

The ground water level needs to be checked when looking at one of these. Levels high enough will push even a concrete tank out of the ground.

Is it just me, or do most of those shelters closely resemble septic tanks?

Sue

Leigh, There is a pressure differential, but it is not in and of itself lethal. The lethal part of a tornado is flying debris. This seems to be one of the myths of tornadoes like opening the windows on your house to allow the pressure to equalize quickly. When opening the windows on a house would allow high speed winds into the structure and help blow the house apart.

http://en.wikipedia.org/wiki/Tornado

Tornado myths are about 3/4s of the way down the page.

Hmmm... the article didn't mention anything about bathtubs...

Sue

FEMA's guide to shelters is pretty good and includes some information on the risks and reasons buildings fail, including pressure differentials:

http://www.fema.gov/library/viewRecord.do?id=1536

Build a Monolithic Dome home and you can mitigate alot of your concerns about tornadoes and othr scurrilous activities of nature. You will lose a few windows and myabe a door but the house isn't going anywhere.

Funny you should mention that.

IMHO a fairly efficient and cost effective way of constructing a shelter against various situations by paying a visit to your local pre-fabricated concrete distributer with an eye toward their larger septic tanks, cisterns and manholes.

A large septic tank can be 10' long, 8' wide and 6'6" high inside. Plant it anywhere from 3' under and half-way exposed with a standard manhole bumped up against one end and you have a workable shelter. If it is half above ground, maybe because of a high water table, you simply berm the exterior.

I'm leaving out a lot of details, like drainage and how to join the main pieces so they stay together and don't leak, but anyone good with their hands and familiar with these materials can do a workmanlike job.

It can be practical DIY job for advanced practitioners. You can rent a backhoe for a weekend at about $200 and dig the hole. If you set it up right gravel cam be poured right into the hole and compacted. Most pre-fabricated concrete manufacturers deliver with a truck that can drop the structures in their final position if they can get close enough to the hole. The key here is to talk it out in detail with the people your buying from and find out what they can, and cannot, do.

Here is another alternative.
http://waltonfeed.com/old/cellar3.html