1.4 Rated capacity and the weakest component

1 Four words that are not synonyms

The confusion between the first two is not academic. A crew that believes the tag shows breaking strength will feel they have a margin they do not have; a crew that believes the design factor entitles them to overload "a bit" has spent the margin that covers wear, shock, angle and the things nobody measured.

2 The weakest-component rule, in the standard's own words

The rule appears in three places, each aimed at a different part of the assembly.

• Chain slings and their attachments. 1910.184(e)(2)(i): hooks, rings, oblong links, pear shaped links, welded or mechanical coupling links or other attachments "shall have a rated capacity at least equal to that of the alloy steel chain with which they are used or the sling shall not be used in excess of the rated capacity of the weakest component." 1926.251(b)(2) states the same duty for construction.
• Web slings and their fittings. 1926.251(e)(4)(i) and 1910.184(i)(3)(i): fittings must be of a minimum breaking strength equal to that of the sling, and free of sharp edges that could damage the webbing.
• Metal mesh handles. 1910.184(g)(2): handles must have a rated capacity at least equal to the metal fabric, and show no deformation after proof testing.

And a prohibition that closes the obvious loophole: 1926.251(b)(3) and 1910.184(e)(2)(ii) forbid job or shop hooks and links, and makeshift fasteners formed from bolts or rods. If it was made in the shop this morning, it has no rated capacity, and an unrated component in the chain makes the whole assembly unrated.

3 Walking the chain

Stand at the hook and follow the load path down, naming the rated capacity of every item you touch. On a routine two-leg pick that list is longer than people expect.

1. 1
   The hoist or crane at the radius and configuration in use — the load chart, not the sticker on the boom.
2. 2
   The hook and its latch.
3. 3
   The master link or gathering ring — 1910.184(b) defines it as the forged or welded steel link used to support all the legs.
4. 4
   Each sling leg, at its rated capacity for the hitch and the angle in use, not its vertical rating.
5. 5
   Every shackle, coupling link and connector between the sling and the load.
6. 6
   Any below-the-hook device — spreader beam, lifting beam, plate clamp, magnet, vacuum lifter — plus its own weight.
7. 7
   The attachment on the load: lifting lugs, eyebolts, trunnions, or the structure the sling is wrapped around.

That last item is the one with no tag on it. A fabricated lifting lug is only as good as its design and its weld, and a padeye welded on site by someone who was not told the load is a component with no rating at all. Where the manufacturer provided lifting points, use those; where somebody made them, find out who checked them.

4 The proof tests the standard actually requires

Proof testing comes up in four separate places in 1926.251, with different multipliers, and mixing them up is common.

Two things worth noticing. The employer, not the manufacturer, is the one who has to hold the record in each case and make it available for examination. And a proof test is a check on workmanship, not a rating — a component that passes one is confirmed to be what it was designed to be, and is still used at the rated capacity on its marking.

5 A worked hook-up

A 9,000 lb skid, two legs of a bridle at a 60-degree sling angle, shackles at the lugs.

1. 1
   Total on the hook: 9,000 lb of load plus roughly 200 lb of slings and shackles = 9,200 lb.
2. 2
   Tension per leg at 60 degrees: (9,200 ÷ 2) × 1.155 = 5,313 lb. Part 3 shows where the 1.155 comes from.
3. 3
   Each sling must have a rated capacity of at least 5,313 lb in the hitch used, at that angle — read from its tag, not converted from a vertical figure.
4. 4
   Each shackle must be rated at least 5,313 lb, from the marking on the shackle body — 1926.251(f)(1).
5. 5
   The master link must carry the full 9,200 lb, because both legs pass through it.
6. 6
   The lugs on the skid must be rated for 5,313 lb each in the direction they are actually pulled — which, at a 60-degree sling angle, is not straight up.

The assembly's capacity is the lowest of those figures, and the item that fails the check is usually not the sling. It is a shackle grabbed off the rack because it fit, or a lug designed for a vertical pull that is being loaded at an angle.

6 When the marking is gone

There is no derating rule for an unmarked component and no procedure for estimating one. 1926.251(a)(2)(iii) prohibits using rigging equipment without the affixed, legible identification markings required by (a)(2)(i), and 1910.184(c)(14) says employers must not use slings without affixed and legible identification markings. That is the end of the conversation: an unmarked sling, shackle or hook is out of service until the manufacturer or an equivalent entity identifies and re-marks it.

This matters because unmarked gear is not usually broken gear — it looks fine, which is exactly why it stays in circulation. A tag rubs off, a stamped shackle wears smooth, a chain sling's identification tag is cut off because it snagged. The rule treats all of those the same way, and the practical answer is Part 4's: a place to put out-of-service gear that is not the same rack as the good gear.