AEng123,

If the "people below" were all of your family what Design Safety factor would you use????

Sometimes its possible to do all the right things and still get bad results

You need to look at standards used for cranes and lifting devices.
We had some spreader bars built, and the design factors were at least 8x.

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P.E. Metallurgy, Plymouth Tube

Thank you for your replies,

I use SF=3 for general purpose spreader bars (From ASME BTH category B lifter, service class 0)
For manbaskets I use SF=5 (From CSA Z150)
So I usually use SF=5 for people underneath a load because the same risk is involved for a manbasket. But I have noticed others use 3,6,8, it is all over the place, so I was curious what other people use and why.
Does anyone know what safety factor automotive lift designers use? I tried looking it up but was not able to find it.

A.M.

Cranes and lifting devices usually have a SF of 2 - 3 (per ASME B30.20).

What do you mean by "holding a load"?

And why is anyone working underneath it?

first rule of risk reduction is to eliminate the risk.
Failure of the static lifting equipment is only one potential cause of failure.

Consequence is very high (death), so acceptable risk of failure needs to be very low to achieve an overall risk level which may be acceptable if no other solution is feasible.

To put it another way, would you work under it??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Something that I used, and seem to be the industry norm for working under a suspended load was to double the rigging used to lift, BUT use "fixed" elements.

For example if four chain falls were suspending an exhaust duct, the load was "shared" with four cables with turnbuckles once it was in location

Mining stuff, typically 5 and for 'down the shaft' stuff... 10. Stipulated by the Mines Act.

Dik

I can't name the standard anymore... too long ago, but for me it was SF=5 against Ultimate Strength.
We had other requirements for SF, some were for ultimate and other were for yield strength.

Littleinch, in my case my designs weren't necessarily that anyone was actually working underneath it at the time of use. The point was that these are above work areas, aka overhead, and therefore had a minimum factor of safety regardless if anyone else but the crane operator was in the room.

--Scott
www.aerornd.com

Quote:

And why is anyone working underneath it?

JME but its more common to work under suspended loads than to ban the practice, many plants have all manner of hanging conveyors, material handling cranes, etc overhead constantly. Many modular cranes on assembly lines are actually themselves suspended many feet from ceiling rafters. At a previous employer several of us got a regular giggle out of stopping tour groups at a particular spot on a main aisle and pointing out the line of 10+ ton engines inching along directly overhead, folks often became uncomfortable and stepped aside quickly. So long as due diligence is given to safety factors, maintenance/safety procedures, and loads/lifts are non-critical there's little need to worry.

Thank you for your replies, I feel satisfied with minimum SF 5 now.

LittleInch: by holding a load I mean for example an automotive hoist or a pair of stands holding up a larger vehicle where people need to be underneath to perform maintenance.

Rather than relying on random opinions from the internet how about getting yourself a copy of the relevant standard?
https://www.asme.org/products/codes-standards/pase...

It is against OSHA regulations for people to work under suspended loads. For people to work under elevated loads, some form of cribbage, tower or other secured means of holding the elevated loads have to be used.

We had to have an annual proof test of a factor of 4 over the nominal working load. I pointed out that we were damaging the rig more in that one annual test than in all the rest of its use. Fell on deaf ears...

Cheers

Greg Locock


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Find out what they used on that pedestrian bridge down in Florida, and whatever it was, use a higher number.

I'm with LittleInch and Chicopee. No one should be under the load. Your lifting beam and rigging may have a sufficient FS but $#!+ Happens! Fortunately in this case no one was hurt.

In addition to a safety factor, consider adding fail-safe measures. Fail-safe measures aim to make situation safe even after a failure.

Thank you everyone for your replies.

MintJulep: that standard does not have design factors that I can see, only proof loads for testing (so at max, SF=2)

ANSI ALCTV for automotive lifts uses SF=3 to ultimate strength

Check out the Crosby catalog for rigging equipment. Data on safe loads and factor of safety are provided. Don't have anybody work under suspended loads.