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Tiedown for Safety and Mission Accomplishment

Sir Isaac Newton’s First Law of Motion states that an object at rest tends to stay at rest and that an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. During a mission rehearsal exercise at the Joint Multinational Readiness Center in Hohenfels, Germany, I observed that Soldiers did not adequately secure vehicle loads to accommodate Newton’s First Law of Motion.

This article is not intended to replace existing technical manuals as a source of information for securing vehicles but to provide leaders and drivers with basic, science-based information and to direct them to examples of proper vehicle tiedowns using chain and ratchet load-binders. This article will look at securing one specific item of equipment, the All Terrain Lifter Army System (ATLAS), a variable-reach, rough-terrain, 10,000-pound lift-capacity forklift (VRRTFL), with a gross vehicle weight of 33,500 pounds.

Why Does It Matter?

In science, laws are events that do not vary; they remain constantly true. Such physical laws are important for us to know so that we do not damage equipment and, more importantly, so that we do not injure or kill Soldiers.

Army equipment is often heavy and bulky. While military vehicles may seem to travel slowly, if we convert speeds measured in miles per hour to speeds measured in feet per second, suddenly things seem to be moving more quickly than we might have first suspected. A vehicle moving 30 miles per hour is actually traveling 44 feet every second. Couple speed with Newton’s Laws, and we find that items on a moving vehicle that appear to be at rest and motionless are not motionless at all. These items move at the same speed as the vehicle moves. This factor is not so important when the driver and vehicle accelerate smoothly, but it becomes highly critical when the driver, vehicle, and load make a sudden stop. Newton more precisely stated that, when objects are in motion, they will continue to move in the same direction and at the same speed, unless some other force—friction, tiedown chains, or some similar force—acts upon them to retard or stop their movement.

So, if we have an ATLAS riding on an M172A1 low-bed trailer, we must have something very strong to hold it to the trailer in the event that the truck and trailer suddenly stop. If we do not have the forklift well secured, its 33,500 pounds of mass may continue to move forward at the speed it was traveling before the sudden stopping force acted upon the truck, the trailer, and the load. During such sudden stops, cargo loads will continue to move, and the force needed to restrain those cargo loads, depending on their speed, can be many times greater than their normal motionless weight. This force is expressed as g-force—the increasing force of gravity on an item as the item accelerates.

Visualize traveling within a convoy down a snow-covered tank trail in a 5-ton tractor towing a low-bed trailer with an ATLAS on it. The convoy speed is a modest 15 miles per hour (22 feet per second). Suddenly, you hit a patch of ice, which instantly causes you to lose control of your truck, and the truck hits a large tree, which very rapidly brings everything to an instant and grinding halt. What is happening behind the tractor on that trailer with the 33,500-pound ATLAS? A moment ago, you were moving along smoothly at a modest speed, and now you are going 0 feet per second. What speed is the forklift going? Did it stop with you? Did it continue to travel along at some speed between 22 and 0 feet per second? What is going to stop the forklift? Will it stop before it goes through the cab of your tractor? Do you have sufficiently strong chains in the proper quantities to hold the ATLAS stationary on the trailer? Do your chains have the needed excess safety capacity? The only thing that is going to stop that forklift mounted on a trailer is to have properly attached restraints of the appropriate size and strength. So, just how should you position the chain assemblies in order to tame this beast?

Chains and Load Binders

A careful examination of the current ATLAS technical manual (TM), TM 10–3930–673–10, incorrectly illustrates the chain used in the tiedown illustration as 0.38-inch chain (Scheme symbol 1-inch) having a 9,000-pound capacity working load limit (WLL). The manual’s sample problem uses a Scheme symbol 2-inch railroad-only chain having a WLL of 13,750 pounds. These chains, both the Scheme symbol 1-inch, 9,000-pound WLL and the Scheme symbol 2-inch, 13,750-pound WLL, are commercially available, but they are not readily identifiable as being available within the Defense Logistics Agency supply system for use with truck transportation. Both are railroad chains, and both are very expensive.

An ATLAS vehicle has 12 tiedown points, each rated at 13,300 pounds. The TM’s example uses a total of eight chains, four restraining forward motion and four restraining aft motion; all chains work to restrain lateral motion and exert force to preclude vertical motion. Many methods can be used to secure a vehicle correctly, but remember that these computations do not fully consider more aggressive driving conditions that are possible in tactical or combat environments. Because the manual’s authors computed the requirement using Army standards made obsolete with the implementation of 49 CFR (Code of Federal Regulations) 393.102 on 1 January 2004, their answer provides a quantity of chains that does not satisfy current restraint requirements.

To get the correct answer, use the U.S. Department of Transportation (DOT) column of the restraint table above. If you use grade 70 steel transport chains,Scheme symbol 1-inch with a WLL of 6,600 pounds, you must use a minimum of 17 chains—10 to restrain forward motion, 6 to restrain aft motion, and 1 to restrain the forklift’s boom and fork assembly. These quantities (less the boom-securing chain) were determined by using the TACOM Life Cycle Management Command formula with a modified rounding rule (illustrated at right). We will need several more chains than the TM reflects. Always round up any fractions to the next even whole number of chains, and maintain symmetry (balance) in your tiedowns. The load needs an equal number of chains on each side (left and right) of the load and the trailer.

When computing the chain requirements, you may use the relatively simple but multistep formula found in TM 10–3930–673–10. It yields good estimates that are conservatively safe. Using this formula, you can change your restraint factors, chain size, and strengths and compute the number of chains you will need for most conditions you may encounter. The formula also permits you to compute requirements based on the chains you have available for a particular load-carrying vehicle. The solution in the sidebar provides the calculation for using Scheme symbol 1-inch chain with a WLL of 6,600 pounds (see table below). It is important that you not attempt direct comparisons of the restraint factors between the various transport modes listed in the table at right because the safety factors and restraint design requirements differ between those modes.

Cautions

Chain standards vary widely within the Department of Defense and industry. To ensure that you have the correct chains on hand, you need to check the types and condition of your chains early, before it is time to move your vehicles and your cargo. If your unit receives a trailer through a lateral transfer, ensure that you have the correct size and quantity of basic issue “transport chains” and that the chains are serviceable. Otherwise, your unit may end up without the correct chains and will have to buy the correct chains with its limited mission funds. While waiting for those chains to arrive, you will not be able to perform your mission. These chains are absolutely essential to the readiness of the trailer and, in turn, your unit.

For transportation load-securing purposes, the industry standard is grade 70 welded, high-strength, carbon-steel chain. Grade 70 chain with links of Scheme symbol 3-inch and larger will, at some periodic link interval (usually one link in every 36 inches of chain), have an embossed (raised) mark of either a 7, 70, or 700, and the chain also will have a manufacturer’s identification symbol or mark. Grade 80 chain has marks of 8, 80, or 800, and grade 100 chain has a mark of 10, 100, or 1,000. Grades 80 and 100 chains are both high-strength, steel-alloy chains. Some chain customers (such as the U.S. Government) may dictate specific color coding and finishing for chains of certain sizes and grades.

As a rule, use only chains you can identify by national stock number (NSN) and that match your TM’s basic issue items or additional authorized item lists. If you cannot identify a chain’s NSN or determine by its grade that it meets Federal specifications, do not use it unless you compute the chain’s restraint factor based on grade 30 proof coil chain—a weak grade of chain.

If a chain shows signs of damage, do not use it! Turn it in to your supply room immediately, and order new chain. What constitutes a damaged chain? Any chain with bent, broken, chipped, cracked, crushed, elongated (stretched), gouged, or twisted links; links having excessively worn bearing surfaces (grooved—inside the individual links); or a chain with a knot in it is a damaged chain. If a chain has grab hooks or other devices on the end, and those items are damaged, the entire chain assembly is unserviceable.

Increasing Restraint

You can gain greater restraint in several ways. You may use more chains, stronger chains, or larger chains, or combine all three. You also can recalculate the number of chains needed by changing the number of g-forces that you believe you want to restrain and then applying the resultant number of chains. You also may apply chains at more efficient angles to gain better balance between the restraints provided in each direction and minimize the number of chains required. Never exceed the tiedown anchor capacities for either the cargo load or the tiedown anchors on the trailer or cargo bed. All chain angles should be between 30 and 45 degrees from the horizontal deck.

Securing the Chains

Each Scheme symbol 1 -inch restraining chain needs a load binder (NSN 3990–01–440–5975). This load binder is stronger than the Scheme symbol 1-inch chain. Always ensure that the strength of the load binder and its attached chains and grab hooks is equal to or greater than the strength of the rest of your securement system. Two of the forward and two of the aft restraining chains must crisscross. Those chains must go from tiedown anchors on the left side of the forklift to the right side of the trailer and from the right side of the forklift to the left side of the trailer. This provides adequate lateral restraint.

The remaining forward restraining chains go from the ATLAS’s tiedown anchors directly to a side anchor point on the trailer at a 30- to 45-degree angle. You want to form two 30- to 45-degree angles. The first should be between the longitudinal axis (the forward and aft line) of the vehicle and the tied-down vehicle’s anchor point. The second should be between the tied down vehicle’s tiedown anchor and the (imaginary) perpendicular (90-degree) angle to the side of the bed on the cargo-carrying vehicle’s side. (This is the lateral component.) These tiedowns provide restraint in the longitudinal, lateral, and vertical dimensions. (See drawing below.)

When combined, the two 45-degree angles reduce the effective restraint provided by any chain by half its rated WLL in any of the three directions. With Scheme symbol 1-inch chain, each 6,600-pound chain’s effective restraint becomes only 3,300 pounds. That is quite a decrease! As we change a chain’s angle, the effective restraint ability of the chain changes as well. (These angular changes have no effect on the actual WLL of the chain.) The technical manual for the ATLAS tells us to assume 45-degree angles.

Although these numbers sound large and impressive, this tiedown plan is only designed to restrain the secured vehicle in the event of “heavy or panic braking” by the load-carrying vehicle. It includes no substantial restraint buffer to guarantee the load will stay on the trailer under more violent conditions. (Granted, although there is a difference between the WLL of a chain or load binder, its proof test, and the minimum breaking strength of a chain, you are not permitted to use any factors except the WLL when planning and physically securing your load according to the criteria of the table below). However, by rounding up to the nearest even whole number of chains, we add more security to our load. The 17th chain serves only to secure the boom and forks from telescoping out under severe acceleration.

Selecting Equipment

Drivers, noncommissioned officers (NCOs), and officers must make responsible, informed risk assessments to mitigate the risks posed by moving heavy loads on wheeled vehicles. They must continuously consider road and weather conditions, convoy speeds, and drivers’ experience. Fewer Scheme symbol 1-inch, grade 70 transport chains may hold an ATLAS while panic breaking under otherwise ideal driving conditions to the satisfaction of the DOT or the Army’s Transportation Engineering Agency (TEA). However, fewer chains may not completely secure the load under more adverse field conditions or during even a minor accident.

Load binders apply tension to the chains. Tension is critical to maximizing the available strength of a chain. Loose chains do not secure a load; they permit the load to shift, which is something you definitely do not want to happen. Further, when a loose chain suddenly becomes taught under extreme acceleration, the tension may exceed the chains’ and the load binders’ WLLs and, quite possibly, even their minimum breaking limits. Drivers must ensure that each load binder closely matches the strength and size of its chain. Any load’s stability will only have the strength of the weakest link among the tiedown anchors, chains, and load binders.

Transport chains are not lightweight chains. Each link is made from linked steel or steel alloy rod; the named size is the measurement of the diameter of the metal rod that forms its links. Pick up a ruler and look at how thick these chain links are. Whether Scheme symbol 1-, Scheme symbol 2-, or Scheme symbol 4-inch, these are not discount store bicycle-locking chains. You can find more information on what the various tiedowns and their component elements should look like in the Military Traffic Management Command Transportation Engineering Agency (MTMCTEA) Pamphlet 55–20, Tiedown Handbook for Truck Movements. However, in doing so, exercise great caution when looking at chain strengths and sizes. A chain’s strength—its WLL—is a function of its size and grade rating (the type of metal and manufacturing process used in forming the metal chain). Consult the Welded Steel Chain Specifications published by the National Association of Chain Manufacturers and the Federal Specification RR–C–271D, Chains and Attachments, Welded and Weldless, for accurate information on the standard size and strengths of chain.

Ratchet-type load binders are preferable to levered load binders. Ratchet load binders are much safer devices for operators to use. If operators and supervisors must use levered load binders, they must ensure that all levered load binders have safety lacing wire to safety-seal all load binder levers. Drivers cannot simply wrap chain around the lever and hope the chain stays in place. Although some drivers do this in the field, it is not a correct technique for securing the levered load binder; you must use the lacing wire to secure the lever. Without using the safety lacing wire to secure the load binder, your chain could come unwrapped from around the lever and become loose while you drive down the road. You definitely do not want a load binder to come loose and release a portion of your load. Check the security of your loads on a regular basis—initially, before you leave your motor park; again, within the first 2 miles of leaving the motor park; and then check load security at every rest halt.

Improving Highway Transportation Standards

The Army’s manuals have been requiring fewer chains than the newest DOT standards require for commercial vehicles driving on U.S. highways. Army manuals should be corrected to align with DOT Federal Motor Carrier Safety Administration Rules and Regulations, 49 CFR, Parts 392 and 393. The Army, at the very least, should use the minimum standards of the DOT highway factors. Yet, is this the best practice for our operators and our equipment? Is it reasonable to assume that field and tactical driving conditions may easily exceed commercial trucking conditions? Probably!

The Army needs to consider doing three things to improve highway transportation load securement. First, use no less than the DOT restraint factor standards with the TACOM formula provided in the ATLAS TM. This computation provides greater restraint than the TEA figures do, which will provide drivers with greater protection and better protect valuable equipment from coming loose in the event of accidents, even relatively minor ones. Second, change the doctrine in Field Manual 55–30, Army Transport Units and Operations, which states that the shipping units provide the tiedown devices. Units no longer do this, so it should be removed from Army doctrine. Transportation units should carry chains on board their trailers in sufficient sizes and quantities to tie down properly any load that they are authorized to move. This will be cheaper than having every unit in the Army purchase chains for all of the vehicles that they might need to move. Third, standardize the size of motor transport chains. Chains much larger than Scheme symbol 2 inch are too difficult for many Soldiers to handle. The rail industry uses Scheme symbol 1- and Scheme symbol 2-inch chains; this would probably be smart for the Army to do. Grade 70 transport chain provides the best overall value. Although higher grades of the same sized chain are stronger, their costs rise more steeply than any corresponding increases in strength.

Unfortunately, within the Army, we continue to have accidents. If you want a greater level of security and safety, you need to consider increasing the size or the number, or both, of the chains and load binders you use to secure your loads against forward motion to levels beyond a mere 0.8 g!

Newton’s First Law of Motion is a law we must understand and live with everyday. Drivers, NCOs, and commissioned officers must fully understand the realities of moving heavy cargo on Army trucks and trailers. It is virtually impossible to secure the heaviest truck loads against every conceivable crash scenario. We need to secure our loads against reasonable driving conditions and risks using the WLLs of our transportation chains, but we definitely need to exceed the minimum standards listed by both DOT and TEA. Their figures are simply too low to adequately protect Soldiers and cargo in more rigorous conditions. This is primarily because DOT regulations have changed and because the calculations are based on heavy breaking in fair weather conditions. However, we all must drive safely and securely, whether in combat, the field, or on the highway.
ALOG

Colonel Neal H. Bralley, USA (Ret.), is an assistant professor of logistics and force management at the Army Command and General Staff College at Fort Leavenworth, Kansas. A graduate of the Army Command and General Staff College and the Naval War College, he served in numerous command and staff positions in Korea, Germany, Saudi Arabia, and the United States.