Why all the crane accidents?

Inspired by this video of a crane accident, although there are many, many more videos and photos out there. The vast majority seem to be due to the crane lifting an excessive load at some excessiive reach that basically tips the crane over.

The math to figure out whether a given lift is safe or not is pretty simple, although it requires accurate data:

-the geometry of the crane’s outrigger/support footprint
-the position of the boom tip relative to that footprint (i.e. where the axis of the lift cable would intersect the ground)
-the weight of the object being lifted

Given that these cranes represent a rather large capital investment, and accidents involving them represent a rather large potential liability for loss of property and life, why do these accidents seem to happen so often?

I’m not asking for sharks with frickin’ laser beams attached to their heads here; it seems like it would be relatively simple to have a cable load sensor, a boom angle/extension sensor, and an on-board computer to do the math in real time and constantly monitor whether the crane is getting anywhere close to tipping. Are such systems rare/nonexistent?

How often is “so often?” There are thousands upon thousands of construction cranes operating all over the world every day. It doesn’t seem like I hear about crane accidents very often to me.

Sometimes they happen because of incorrect rigging of the load, and sometimes the cranes are not assembled correctly and have weaker-than-expected joints. This was the cause of a deadly crane collapse in New York a few years back – also turned out they were bribing the crane inspectors.

Sometimes unexpected wind can cause the effective load to drastically increase, especially if you’re lifting a large flat thing.

The weight of the load is not always known or knowable.

The stability of the ground on which the crane rests is not always known or knowable.

There may be obstructions that prevent the crane from being in the optimal, or even good position.

wind is also important for the crane and the load at various heights.

big blue

Accidents with big cranes that do big-dollar damage and take lives (like this one) do indeed make national news, but small ones - like the one in my OP - may not even be noticed by local news.

FWIW, “Fail Crane” is a long-standing internet meme.

Having been a crane operator for a few years I might be able to answer some of your questions.

For now we will speak of only motor cranes as that is what I operated and a completely different machine than a tower crane.

There are indeed gauges and displays showing load line weights, speed of ascent and descent of load, and boom angle. It is imperative that the operator know the limits of his particular machine.

Purely anectdotal, But most accidents I have seen are not mechanical as in a boom breaking or load line snap. Almost all are tipping as shown in your example. The cause of most of these has been footing. The ground gives way under the outriggers. Ground can be hard as rock on top but you or any computer can’t tell what is under the surface.

The other is exceeding reach and center of gravity. This can be attributed to operator error. You don’t need a computer to tell you. That comes with experience.

And yes I stood one on it’s outriggers ONCE!
On edit… what they said

As a former designer of elevated material handling equipment (boom and bridge cranes, telescopic forklifts, aerial manlifts, et cetea) I’ll expand on Craneop2’s excellent post. While it would be feasible to put electronic measurement devices on cranes that link to a control system (and I actually worked on the “envelope management system” for one large telescopic manlift which prevented exceeding the load envelope), it would also add a lot of cost to the design, and would also transfer liability from the operator (who is licensed and provided load charts for proper operation) to the manufacturer, who now by default assumes liability should the EMS fail to prevent the vehicle from tipping. As you can guess, this isn’t a feature that manufacturers are particularly enthused about implementing, and the margin on cranes and other material handling equipment isn’t large, nor do they sell enough volume to invest millions into design and test of such a system unless there is a market ready to pay for it.

The other thing to consider is that cranes and handling equipment are often modified in the field, or are used in ways that the original designers did not intend or analyze for, especially unlicensed cranes and forktrucks that don’t require periodic inspection. If you had a limit switch on a boom and it was preventing the operator from performing an operation that he believed the crane to be capable of, he’d probably just disable the thing. Of course, you can make a control system failsafe, such that if it doesn’t get feedback from the limit switch it goes into a safe mode that prevents operation, but the reality is that there isn’t much demand for this. A good experienced operator is actually a very sensitive controller, and provided he isn’t drunk, high, under extreme pressure to load a barge as quickly as possible, or operating equipment that has not been properly maintained and inspected, is probably more reliable than the type of control system that would be designed by a crane manufacturer, just as a good driver can operate a car more precisely with the traction control off.

True story: while working at one of the major telescopic material handling companies, we got a call from marketing asking what safety factors were used in designing the boom. Factors of safety, for those who don’t know, are factors that you apply to the loads (or take away from allowables) to account for the fact that your analysis may not capture the absolute worst loading case for structural failure or tipping, and are also often intended to give a margin against damage tolerance; basically, they are your safety cushion against a failure that pushes you just past your design envelope. For structural safety on these machines, it was typically something like FS[SUB]Yield[/SUB]=1.25 for non-critical parts and FS[SUB]Yield[/SUB]=1.5 for critical structures, with a FS[SUB]Static Tipping[/SUB]=1.1 and a 1.5 dynamic load factor. You get the idea; there is some margin built in to protect against manufacturing defects, minor design analysis errors, in-use damage, and your basic average idiocy.

Well, it turned out that marketing wanted to up the rating on our machines by removing all of the design factors of safety! That’s right; our 10,000 lb machine would now be rated for 15,000, but if you lifted 15,001, it would collapse. When we explained in plain terms why that was not a practical solution (uncertainty in analysis, the precision of measuring the load being lifted, et cetera), the marketing group argued that they would just put a more visible sticker in the operator’s cage warning against exceeding the load; maybe yellow with orange text. :smack:

Stranger

Scary story, Stranger. Did marketing win in the end? That was obviously litigation waiting to happen. It’s hard to imagine that anyone with a rudimentary education doesn’t understand the concept of over-engineering for safety.

I can’t help but wonder if this is not a consequence of modern musical chairs management. In the modern era, a manager is presumed to be capable of managing anything - content knowledge of the field being managed is not required. Typically, such managers swan into a position for only a year or two before swanning off somewhere else. Because of this, they are under pressure to get results fast, so all decisions become focussed on the short-term. There is no risk to them of long term failure, because if things go to crap they are long out of the place, but the company has to carry the can.

That’s terrifying. I’m strongly reminded of Richard Feynman’s analysis of the NASA management in appendix F of the Rogers Commission report, in the wake of the Challenger disaster.

Your post has sparked my curiosity, Stranger. You mention you’re a former designer of material handlers etc. If you’ll pardon my asking, how long since you were in that role?
I’m simply trying to determine whether you got out of the way before H&S started taking everything and wrapping it in bubblewrap (figuratively) to protect us from ourselves. I’m guessing not, since you mention envelope management systems, which I’ve only come across in newer telehandlers. Older ones might have a load monitoring system, but was usually no more than a few coloured leds and maybe a buzzer, linked to a pressure sensor on the rear axle to give an indication of how close the machine was to tipping. It’s only recently that the bloody things started interfering with the controls, refusing to let you raise the boom etc. once it passes a certain load.
I’ve never had the chance to operate a crane, although I did get a quick tour of the cab of one, a Leibherr 100 tonner, in which the operator was pointing out the very fancy high tech computerised load monitor, which could (apparently) tell the driver, in real time, how much weight was hanging on the end of the jib, as well as the maximum permissible weight for the current jib angle, extension and rotation, and even helpfully calculated the max vs current as a percentage. I seem to remember being told that it would not let the boom extend or lower further than the computer deemed acceptable, but would let the operator override it in ‘creep’ mode, whilst beeping furiously as a reminder that “This is on your head, I warned you!”
I was just wondering if you had any knowledge, or could speculate how such a system might work? My guess was that the computer monitors the hydraulic pressure in the outrigger jacks, and uses the variations to work out how close the crane is to it’s balance limits. Am I near the mark, or way off?
I did ask the operator, but he confessed to not having “…a scooby, I just drive 'em, I can’t build 'em.” He did do a bloody good job of driving it though, so I forgave him for not knowing the intricacies of how it worked!

Just a small bit about Big Blue above: it was on an engineered foundation, but was being used in much higher wind conditions than normal. The foundation was fine for overall load, but the eccentricity did it in.

Stranger, that’s horrible, but not terribly surprising.