At Tornado Alley Armor we have never had a customer have to deal with lighting and hanging power lines on their safe room after a tornado. This really isn’t something to be highly concerned about. The chance that you could have live wires lying across your storm shelter after a tornado is almost non-existent. It just doesn’t happen. But, for those of you that may worry here are a few things to help reassure you:
The following is an excerpt from the National Storm Shelter Association Standard for the Design, Construction, and Performance of Storm Shelters:
Concerns over safety in lightning storms for occupants of storm shelters have led to searches for applicable science or expert opinion. Little published information has been found that addresses directly the shelter safety issue. The advice of engineers and scientists with extensive research experience in lightning safety is reflected in this Standard. Some evidence has been provided by experts on the subject of metal structures indicating that metal enclosures shield the interior from the effects of outside sources of electricity. The public intuitively acknowledges this principle when driving automobiles during thunderstorms. The “metal box” represented by a conventional car or van yields a skin effect that becomes the conductor and protects the occupants.
BG Claude B. Donovan, project officer for development of the Army’s Bradley fighting vehicle, points out that “… tanks and armored vehicles get hit by lightening all the time, and in many cases they are uploaded with their basic loads of ammunition, pyrotechnics, and fuel. There isn’t even a conscious effort to make the ammo or packing materials conductors or insulators, so grounding must not be a big factor.”
Additional safety measures you can take if you are still concerned are grounding and adding high density rubber floor mats to stand on. You can also add electrician grade insulated gloves to the safe room in case live electrical lines would end up lying on the safe room.
Your safe rooms have apparently passed the impact tests. However, I’m concerned more about them being anchored to the floor so that if the house is total blown off its foundation, the safe room stays attached to the floor. How are they anchored? I’m looking at putting a safe room in my garage. Do you have to pour an additional slab of some kind, or is it simply anchored to the existing floor of the garage?
Jerry,
We anchor the safe room to your existing reinforced slab of adequate mass and geometry by using wedge anchors. FEMA recommends 10” maximum spacing, our spacing is 6-10-10-6-10-10-6…you get the idea. Each anchor “officially” provides around 3500 lbs of hold down resistance and even more shear resistance. However, we installed a safe room for a Mechanical Engineer from Hilti ( one of the world leaders in bolting and anchoring fasteners), and he told us they and other manufacturers use a safety factor of 13 when publishing their spec sheets. So in reality, each bolt literally provides about 50k lbs of hold down before it fails, and the number of bolts in your storm shelter is determined by the size you order.
Thanks for your question,
Leslie