FMCSA Section 393.106 (d) explains that the aggregate (total) working load limit (WLL) of all tiedowns used to secure an article(s) against movement must be at least half the weight of the article(s) being secured. The aggregate WLL is the sum of:
- One-half the WLL of each tiedown that goes from an anchor point on the vehicle to an anchor point on the cargo. Industry refers to this as a “direct” tiedown and per 393.106 (d) you only get to use half the value of the rated WLL.
- One-half the WLL of each tiedown that is attached to an anchor point on the vehicle, passes through, over, or around the article of cargo, and is then attached to an anchor point on the same side of the vehicle. This is another example of a “direct” tiedown, and you only get to use half the value of the rated WLL.
- The WLL for each tiedown that goes from an anchor point on the vehicle, through, over, or around the article of cargo, and then attaches to another anchor point on the other side of the vehicle. Industry refers to this as an “indirect” tiedown and per 393.104 (d) you get to use the full value of the rated WLL.
FMCSA Section 393.108 (a) explains that the WLL of a tiedown is the lowest WLL of any of its components or the WLL of the anchor points.
You can have a 6600# WLL chain, but if you have a 4700# WLL binder your “tiedown” is now valued at 4700 lbs.
Always be aware of the value given to anchor points either on the trailer or the equipment you attach to. Your overall strength is only as good as its weakest link.
FMCSA Section 393.108 (b) explains that the WLL of a tiedown may be determined by the marking or by using the tables in this section. The values listed in the tables are to be used when the tiedown is not marked by the manufacturer.
A good example of this section is to look at synthetic web tiedowns. If the tiedown is not marked either with a stencil and/or a tag, the tables found in Section 393.108(b) will assign the WLL as follows: 2” wide webbing – 2000 lbs., 3” wide webbing – 3000 lbs., 4” wide webbing – 4000 lbs.
Always be aware of tiedowns with or without a WLL limit assigned by the manufacturer.
Did you know that putting a half twist in a strap will reduce wind flutter and extend the life of the strap? Just try not to let the twist reduce the width of the strap where it contacts the load, would hate to see a 4” wide strap be valued as a 2” strap because of a twist.
Indirect tiedowns and the effects of angles: As discussed with FMCSA Section 393.106 (d), indirect tiedowns pass from one side of the vehicle to the other. Thus, the tiedown is indirectly applying forces to the cargo to stay put on the vehicle. This is a very common and effective means of load securement. However, the angle from the horizontal (tiedown to vehicle) has an enormous influence on load securement.
If the angle is 90 degrees, the effective downward pressure is 100% of the tiedown tension.
If the angle is 60 degrees, the effective downward pressure is reduced to 87% of the tiedown tension.
If the angle is 45 degrees, the effective downward pressure is reduced to 71% of the tiedown tension.
If the angle is 30 degrees, the effective downward pressure is reduced to 50% of the tiedown tension.
It is the owner’s and user’s responsibility to determine the suitability of a product for any particular use. Check all applicable industry, trade associations, federal, state and local regulations. Read all operating instructions and warnings carefully. Ultimately it is the driver’s responsibility to make certain that the cargo being hauled is properly secured.
Be sure to make it a priority to inspect load securement products before each use. The Commercial Vehicle Safety Alliance (CVSA) works with a tiedown defect table for chain, wire rope, fiber rope, synthetic webbing, fitting or attachment, and anchor points.
If a 4” synthetic web tiedown contains cuts, burns, and/or holes through the webbing which total more than ¾” it will be considered Out-of-Service.
Cuts on same edge are not additive.
Cuts on opposite edges are additive.
Cuts and holes at different locations across the width are additive.