Why does nobody talk about the wind at the 200 foot mark?

I was on a job in Kansas City last week, setting steel for a new warehouse. I've been running a tower crane for about 8 years now, and I always trusted the wind meter on the ground. My load was a 12-ton beam, and everything felt fine from the cab. But when I got it up to the top, maybe 220 feet, the load started to swing and dance in a way the ground meter just didn't show. My spotter on the radio finally said, 'It's a whole different breeze up here, Jess.' That was the lightbulb. I was relying on a tool that wasn't telling me the full story for the part of the lift that mattered most. Now I'm thinking I need a second meter up high, or at least to watch the flags on nearby buildings way more. Has anyone else set up a better system for reading wind at height?

3 comments

3 Comments

jamiehayes26d ago

Hold up, is this really a common problem? I get that wind changes with height, but on a normal clear day, is the difference at 200 feet enough to turn a safe lift into a dangerous one? Most of those ground meters have a factor built in for height, right? I've seen guys fly flags on the crane jib itself as a cheap check. Seems like if it was a major issue, the safety rules would already require a high-up sensor. Maybe you just hit a weird gust that day.

jenny_white2126d ago

Forget weird gusts, the math is scary simple. Wind speed can increase by 20% or more every 100 feet you go up. So your 10 mph breeze on the ground is easily 15 mph or higher at the hook. That extra force on a big sail of a load is huge. Those ground meter corrections are just guesses for normal weather, not for real site conditions. A flag on the jib tells you direction, but not if you're already over the limit the second you start the lift.

julias4426d ago

Yeah, that "flag on the jib" check Jamie mentioned is exactly what we used to do. @jenny_white21 is totally right though, it shows direction but not force. We got caught once where the ground wind felt fine, but the load started spinning bad once it got up there. Now we use a cheap handheld meter and take a reading from the highest safe point we can reach before the lift, like from a manlift or the roof. It's not perfect but it gives a way better number than just guessing from the ground. What do you guys do to check the wind up high?