# Ice falling from buildings?January 7, 2009 7:20 PM   Subscribe

Ice falling from tall buildings filter. Help me lay to rest a question that has plagued my wife. We live in Chicago, with lots of tall buildings. Ice falls off of the buildings from time to time and about once a year, some poor bastard gets mushed. Where in terms of physics and I suppose statistics would be the safest place to walk down the sidewalk: as close to the building as possible? The middle of the sidewalk? The far edge? Does it depend on building height?
posted by Ponderance to Science & Nature (16 answers total) 8 users marked this as a favorite

I wondered this too, and asked an architect friend. Apparently, it's a known "puzzle," from which students do calculations to determine the answer to your very question.

These Chicago ice-crushings occur in the Loop, and usually the buildings from which they happen are more than a dozen stories high. Basically, there are so many variables - the slope of buildings, wind patterns, wind speed, wind direction, the rapidity of melting, (etc) - that there's really no survival strategy, except to always take taxis.
posted by Dee Xtrovert at 7:30 PM on January 7, 2009

Can't help with the physics calculations in question, but just wanted to mention that the height of the building doesn't necessarily matter for the deadliness of the ice fall. My mom in law was nearly killed last winter (it was Feb. or March) by an ice floe that slid from the roof of her shop, which was only about 15 feet high. The sheet of ice was about 6-8 inches thick and about 3 feet square. Slid off the roof from the vibration when she shut her back door and hit her clean on top of the head. She had a concussion and a split scalp for which she needed a lot of stitches, but miraculously, her skull didn't cave in. Doctors told her she should've been killed & couldn't figure out why she wasn't; considering that it was a couple hundred pounds of sharp and solid awfulness she was hit with.
posted by cuddles.mcsnuggy at 8:02 PM on January 7, 2009

The signs say to watch for falling ice, and in conditions where falling ice is possible or I see other ice on the ground, I take that strategy. I figure that if I look up I can see any major piece coming towards me as long as I look up pretty sharply. I have not yet been killed, although I also haven't had to dodge any falling ice.
posted by iknowizbirfmark at 9:42 PM on January 7, 2009

Thinking about it, it should depend on the building. If the building is totally vertical like say the World Trade Centers you should stand further away because the ice will fall near the edge and nothing will push it away. Whereas if the sides are not totally vertical like the Chrysler Building the ice will fall, hit an edge and bounce further away from the building, therefor you would be safer closer. So my here are your choices a) get a helmet b) take taxies c) walk around looking up d) don't worry about it. I recommend d.
posted by DJWeezy at 9:43 PM on January 7, 2009

The aerodynamics of the ice must matter: a conical icicle may fall like an arrow, while a clump might drift like a knuckleball.
posted by Rumple at 9:49 PM on January 7, 2009

You know, this sounds like a good idea for Mythbusters. Maybe they could give it a whack.
posted by Ghidorah at 10:30 PM on January 7, 2009 [5 favorites]

I've been hit by ice from a 2nd story... slanty part of a building while wearing a snowboarding helmet, and it knocked me Right. Down.
I didn't hear nor did I see it coming, so if it were just falling through the air from a decent height, you would need to walk looking straight up 100% of the time to have any chance of dodging. Or maybe you'd get smacked in the face for your trouble.

But. Falling ice is only a problem at certain times of year, it seems. Spring, mainly. And the odds are definitely on your side.

If I were playing an ice-dodging game I would stick close to the building. It's usually free of ice fragments and drips, so something must be helping. Maybe a big ice sheet would twist and hit the building and bounce away from it.
Maybe the wind has more to say about it than anything else, and wind between buildings is so unpredictable that all bets are off unless you're Spiderman, but then you're not walking anyway.
posted by Acari at 11:09 PM on January 7, 2009

Maybe this sounds dumb, but what about bringing an umbrella? Though probably not effective, it might make it slide away from your head.

I second MythBusters.
posted by big open mouth at 11:31 PM on January 7, 2009

Oh, also, I think for the most part ice won't fall straight down unless it's icicles in which case they'd go directly under the edge of the building. As for ice, if there's a really strong wind blowing then *maybe* it would hit the building, but for the most part I think ice comes off in sheets. In sliding they would probably gain momentum and end up landing beyond the edge of the overhang(if there is one). I'm pretty sure the bigger the sheet the farther it would fly, so closer to the building would be better.
posted by big open mouth at 11:35 PM on January 7, 2009

there's really no survival strategy, except to always take taxis

Chicago also has subway portions of the "L", and the Pedway.

I really don't think there's a simple rule possible for this. One of the most notorious ice kills was when a big floe slid off the curved roofline of the Neiman Marcus building. The physics for that must dictate a pretty close course along the wall. Other chunks may attach to cornices and also fall straight down. Still others may be subject to surface effects, or aerodynamic forces. When a glass window fell off the CNA building a number of years back, it found its way all the way to the opposite sidewalk (where it killed decapitated a woman walking with her grandson). Anything with enough surface area to catch the wind must have a wider potential landing zone.

I think I would also stick close to the building. There's probably more chance of the building itself breaking up the ice in some way, either against the wall or against some projection like a sign. On the other hand, there might be more stuff in that area so I'd be subjecting myself to a higher range of incidents.

Mainly I'd play the odds by being extra careful on those melty days.

I could also invest some time in advocacy for New York-style setback requirements, so most ice would land harmlessly on a lower roof, and the Loop wouldn't feel quite so imposingly canyonlike.
posted by dhartung at 11:36 PM on January 7, 2009

there's really no survival strategy, except to always take taxis.

But which is higher? The risk from falling ice, or the risk from a car accident?
posted by devnull at 2:56 AM on January 8, 2009 [2 favorites]

The signs say to watch for falling ice, and in conditions where falling ice is possible or I see other ice on the ground, I take that strategy. I figure that if I look up I can see any major piece coming towards me as long as I look up pretty sharply. I have not yet been killed, although I also haven't had to dodge any falling ice.

I have somewhat the same response as devnull. I'd bet this is more hazardous to the degree that it diminishes attention to horizontal threats.

In fact, I would hazard -- haw! -- that the best strategy for diminishing the risk of death during periods of ice signage is to (a) walk as much as you can, as opposed to riding taxis (cardio), and (b) use the signs to remind yourself to obey traffic/crossing signs.
posted by Clyde Mnestra at 4:27 AM on January 8, 2009

Just run really fast everywhere whenever you're inside the loop.
posted by allkindsoftime at 5:02 AM on January 8, 2009

Walking around downtown Toronto and Ottawa we see these signs too, they usually cause me to look up nervously, then go back to my business. Statistically, the handful (or less? in Toronto this stuff is rarely heard of) of people represent a very tiny portion of individual walking events. Try and maybe think in those terms, that the chance of you being hit with ice on any given walk is so small as to not be worth thinking about.
posted by dnesan at 8:11 AM on January 8, 2009

If it's really only one person a year or so, then given the number of pedestrians killed by cars (48 in 2006 in Chicago, source), you're probably better off watching the street that the skies.
posted by echo target at 8:50 AM on January 8, 2009

My wife is thankful and delighted by the responses, thank you all. She has opted for the hard-hat.
posted by Ponderance at 7:18 PM on January 9, 2009

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