MELISSA BLOCK, HOST:
From NPR News this is ALL THINGS CONSIDERED. I'm Melissa Block.
ROBERT SIEGEL, HOST:
And I'm Robert Siegel. This week, civil engineer Timothy Marshall was surveying tornado damage in Moore, Okla., for the third time.
BLOCK: He first went in after tornadoes blasted through in 1999, and again in 2003. And he joins me to talk about what he found. Mr. Marshall, welcome to the program.
TIMOTHY MARSHALL: Thank you for having me.
BLOCK: When you looked at the structures in Moore, did you see any difference in what either survived the tornado or didn't survive the tornado compared with your previous visits there?
MARSHALL: I did not see any improvement in the overall building stock in Moore. And that's sort of disheartening, especially after they've been struck with two prior violent tornadoes. What I did see as a plus, though, was that there were thousands of people who had tornado shelters. And that is a great improvement over the last 15 to 18 years. I mean, we spoke to many people who survived. Their houses were leveled. They would've been seriously injured or killed. And certainly they agree that these shelters were worth every penny that they paid for them.
BLOCK: You mentioned that you were concerned that it didn't appear that houses themselves were constructed any more safely with any more structural strengthening to withstand a storm than you had seen before. What would you be looking for that would indicate to you this housing stock was built better and it did better in this storm.
MARSHALL: Well, certainly there are the standard building code, which is a 90-mile-per-hour 3-second gust at 10 meters above the ground. That's a standard. And what we look for specifically were that around the perimeter of the house where the walls are attached to the foundation, building code calls for anchor bolts being spaced at least every six feet and twice at the corners. And we saw very few homes that had been bolted down.
A lot of times there were substitutes for what we call a shot pin, which is a pin that's shot through a wall plate or a cut nail which is driven by hand into the board, the wall that is around the perimeter. And then when we go above that and look at how the wall studs were attached we found many wall studs were just straight nailed in and they were easily pulled out. So we saw just rows of nails standing up where the walls became detached.
It was a horrible feeling to see these houses constructed so poorly.
BLOCK: I was wondering how hard it is to walk back why houses fail in storms like this, you know, what the fatal flaws are. When the damage is so extensive, how can you find the clues that tell you why a house was destroyed?
MARSHALL: Well, even a house that is no longer there provides ample evidence for us. For example, those houses that were anchored - and I use that term loosely - with a cut nail, as the cut nail is dragged across the slab it scars and leaves a mark on the slab. So we can tell which direction even the wall failed.
BLOCK: Did you look at the damage of the two elementary schools that were destroyed?
BLOCK: And what did you see?
MARSHALL: Well, these schools had been designed for the building code of 90 miles per hour. And we found a number of fatal flaws in the construction, especially with the concrete masonry unit walls otherwise known as CMU. There were many unreinforced walls and they did not have the steel rebar that goes into them or the grout that goes into them to protect them against anything more than a 90-mile-per-hour wind. And that's disheartening in a way because schools obviously are where children are congregated. And here we have just a standard type building with no real area of safety.
Now fortunately, they had interior hallways which did provide some protection but it wasn't a shelter, per se.
BLOCK: Um-hum. And in one of those cases I believe it was an interior wall of a hallway that collapsed and killed a number of children at Plaza Towers.
MARSHALL: That's correct. I mean, unreinforced concrete masonry kills. Children should not die in schools. To me that is - especially when you have a tornado coming - I don't care how strong the tornado is, there are ways that you can have a shelter to withstand that and you can save the children.
BLOCK: Timothy Marshall is a civil engineer based in Dallas. Mr. Marshall, thanks for being with us.
MARSHALL: Thank you very much. Transcript provided by NPR, Copyright NPR.