Cargo Securement: the Working-Load-Limit Math

The g-forces the rule is built on

The title of this guide says "80 percent" because that is the phrase drivers use for the forward case. The regulation is more precise, and the precision matters. 49 CFR 393.102(a)(1) requires tiedown assemblies, including chains, wire rope, steel strapping, synthetic webbing, and cordage, and other attachment devices, to be designed, installed, and maintained so the maximum forces acting on them do not exceed the manufacturer's breaking strength rating under three conditions, applied separately: 0.8 g deceleration in the forward direction, 0.5 g acceleration in the rearward direction, and 0.5 g acceleration in a lateral direction.

That 0.8 g figure is a breaking-strength test, not a working-load-limit test. 393.102(a)(2) is the working-load-limit paragraph. The forces must not exceed the working load limit under 0.435 g deceleration forward, 0.5 g acceleration rearward, and 0.25 g acceleration lateral, again applied separately. If you only remember "80 percent forward," you have remembered the breaking-strength case and dropped the WLL case. If you only remember "half the weight," you have remembered 393.106 and dropped 393.102. Both sentences stay.

There is a third force in the same section. 393.102(b) says securement systems must provide a downward force equivalent to at least 20 percent of the weight of the article if the article is not fully contained within the structure of the vehicle. A load inside a van with walls doing the containing work is not the same case as a machine on a flatbed. The downward-force sentence is why a strap that merely drapes across a tall article, with almost no downward component, is not "on there" in any sense the rule cares about.

393.102(c) also allows equivalent means: cargo immobilized so it cannot shift or tip enough to hurt stability or maneuverability, cargo in a sided vehicle with walls of adequate strength so articles cannot shift or tip to that extent, or cargo secured under 393.104 through 393.136. "Equivalent" is not "it sat still while I walked around the trailer."

Aggregate WLL at least half the cargo weight

49 CFR 393.106(d) states the aggregate working load limit of tiedowns used to secure an article or group of articles against movement must be at least one-half times the weight of the article or group of articles. That is the "half the weight" shorthand. It is an aggregate. You add up the credit each tiedown is allowed to contribute. You do not ask whether one favorite strap is rated at half the machine by itself, and you do not add the breaking strength.

The same paragraph tells you what you may add. One-half the working load limit of each tiedown that goes from an anchor point on the vehicle to an anchor point on the article. One-half the working load limit of each tiedown that attaches to an anchor point, passes through, over, or around the article, and then attaches to an anchor point on the same side of the vehicle. The full working load limit of each tiedown that goes from an anchor point, through, over, or around the article, and then attaches to an anchor point on the other side of the vehicle.

Read those three clauses before you total a number. A chain bolted to the machine and to one pocket is not counted the same way as a strap that goes over the top and is winched to the opposite rail. Two straps that both hook on the same side do not become four times a tag just because you own four hooks. The regulation already did the "how much counts" step. Use it.

An example that is arithmetic, not a legal minimum beyond the text: a 10,000-pound article needs an aggregate WLL of at least 5,000 pounds under the half-weight sentence. If each strap that crosses to the other side has a 4,000-pound WLL tag, each such strap contributes 4,000 pounds to the aggregate under 393.106(d)(3). Two of them aggregate 8,000, which clears half of 10,000 on that sentence alone. A strap that only attaches on one side contributes half of its tag under 393.106(d)(2), so a 4,000-pound tag on that attachment contributes 2,000, not 4,000. The count in 393.110 can still require more tiedowns than the aggregate math. Clearing half the weight with one very strong strap does not erase the length rule. And this arithmetic does not replace the 0.8 g breaking-strength case or a commodity section.

How many tiedowns by length and weight

49 CFR 393.110 is in addition to 393.106. The minimum number depends on length and on whether the article is blocked against forward movement.

When the article is not blocked or positioned to prevent forward movement by a headerboard, bulkhead, other cargo positioned to prevent movement, or another appropriate blocking device, 393.110(b) requires at least: one tiedown for an article 5 feet or less in length and 1,100 pounds or less; two tiedowns if the article is 5 feet or less and more than 1,100 pounds; two tiedowns if the article is longer than 5 feet but less than or equal to 10 feet, whatever it weighs; and, if the article is longer than 10 feet, two tiedowns plus one additional tiedown for every 10 feet of article length, or fraction thereof, beyond the first 10 feet.

The blocking exception is 393.110(c), and it is not optional to mention. If the article is blocked, braced, or immobilized to prevent forward movement by a headerboard, bulkhead, other articles which are adequately secured, or another appropriate method, it must be secured by at least one tiedown for every 10 feet of article length, or fraction thereof. That is a different count. A 20-foot article blocked forward is not automatically the unblocked formula. Use the paragraph that matches the way the freight is actually sitting. A loose stack of pallets in front of the machine is not a headerboard.

393.110(d) says these number rules do not apply to certain special-purpose vehicles carrying articles that, because of design, size, shape, or weight, must be fastened by special methods, such as some machinery or fabricated structural items. The article still has to be securely and adequately fastened. "Special purpose" is not a waiver you declare because the winches are inconvenient.

Fraction thereof means a partial extra 10 feet still demands the extra tiedown in the paragraph that uses that phrase. Do not round a 10-foot-1-inch article down to a clean 10.

Direct versus indirect, and a low angle

Direct and indirect are the shop words for the attachments 393.106(d) already splits. A tiedown that ends on the cargo is credited at half its WLL under (d)(1). A tiedown that goes over the cargo and reaches the other side is credited at its full WLL under (d)(3). A tiedown that comes back to the same side is credited at half under (d)(2). That is the regulation's credit rule. It is not a brand chart.

Angle is a separate physical fact. A strap that leaves the rail and barely climbs before it lies flat across the deck is not producing the downward force a strap at a steep angle produces. 393.102(b) already requires a downward force equal to at least 20 percent of the article's weight when the article is not fully contained in the vehicle structure. A nearly flat strap is a poor way to get there. FMCSA's cargo-securement handbook illustrates how angle changes the effect of a tiedown. This page will not print a homemade percent table, and it will not convert degrees into a percent from memory. If you need the illustrated angle effect, use the current handbook. Do not tape a yard-made chart to the headache rack and call it the CFR.

The practical instruction is smaller than a table. Keep the strap steep enough that it is actually holding the freight down, protect it from the edge that would cut it, and then do the aggregate math with the credit 393.106 allows. A steep strap with an unreadable tag is still not a number. A flat strap with a beautiful tag is still a weak downward force.

Edge protection when the strap would cut

49 CFR 393.104(f)(4) requires edge protection whenever a tiedown would be subject to abrasion or cutting at the point where it touches an article of cargo. The edge protection must resist abrasion, cutting, and crushing. A cardboard corner on a sharp steel edge is not automatically that device. The rule is the performance, not the habit.

393.104(b) also prohibits damaged securement devices. Cracks or cuts that adversely affect performance, including reducing the working load limit, mean the device is not in proper working order. A cut strap does not keep the WLL printed on the tag that is still sewn to the undamaged end. Retire it. 393.104(f)(1) says tiedowns must not contain knots. A knot is not a repair.

393.104(f)(3) says each tiedown must be attached and secured so it cannot become loose, unfasten, open, or release in transit. A winch bar left in the winch is not the topic. A hook that is tipped open on the rail is the topic. Recheck after the first miles, because straps settle. The regulation does not give you a mile marker for that recheck. The load either stays tight or it does not.

Commodity rules that override the general count

393.106(a) says the rules in that section apply to the cargo types covered by the commodity-specific rules of 393.116 through 393.136, and that those commodity-specific rules take precedence over the general requirements when additional requirements are given for a listed commodity. The general count is the floor for articles that have no extra section. It is not a permission slip for a coil, a paper roll, logs, or heavy vehicles and equipment.

Coil steel hauling requirements is the coil page. How to secure flatbed loads is the broader flatbed page. Do not finish a coil with "it is under 10 feet, so two straps" and call 393.110 the last word. Open the commodity section. If that section adds tiedowns, blocking, or friction devices, those additions are the rule.

Nothing on this page is a recommendation of a webbing brand, a chain grade to buy, or a distributor. The tag on the device you already own, read against 393.106 and 393.108, is the rating. 393.108 contains default working-load-limit tables for certain unmarked tiedowns. This page does not reprint those tables, because a remembered chain size is an invented number the moment the table is not in front of you. If the tag cannot be read and you have not applied 393.108 to that exact device, you do not have a WLL to put in the aggregate. Add a tiedown you can identify, or do not haul the article.

A machine that "didn't move" while you pulled out of the dock has not been shown to meet breaking strength or working load limit. The calculation is boring on purpose. Boring is the alternative to explaining a shifted load at the scale.

Frequently Asked Questions