Quick Answer: What causes safety and productivity problems when manually handling very heavy loads?
Issues with managing heavy loads occur when a lifting action involves mass, balance or weight distribution, grip security, horizontal reach, or frequency exceeding what is referred to as human biomechanical capacity. That term considers that no matter how strong someone is, there may be items in a manufacturing setting that they simply cannot lift safely or repeatedly.
Workplace injuries (and the resulting production slowdowns or pauses) commonly occur when awkward body postures during lifting actions, excessive reaching, or lifting unstable objects put excessive force on the person’s musculoskeletal system (frequently their back). The scenario can arise with one especially difficult lifting task, but it more often develops as the cumulative damage from many repetitive lifts.
Traditional training for manufacturing personnel tends to emphasize proper lifting techniques (we’re all familiar with the advice, “Lift with your legs, not your back.”), but real-world requirements often push that advice to the back burner. Tight production schedules and fixed equipment footprints sometimes force personnel into improvised, unapproved lifting techniques and workarounds that may help them complete a task but cause immediate injuries or long-term, cumulative physical damage.
This guide goes beyond proper lifting techniques and employee training to explain the factors that push an item beyond the point where it can be safely handled.
Why Can’t Training Fix an Inherently Unsafe Lift?
The answer to this question centers on the word “inherently.” Some items simply have physical characteristics that even the most technically precise lifting technique cannot overcome. These items put the employee at a severe mechanical disadvantage, especially if retrieving or placing them requires holding them away from the body for any period.
You can understand this physical challenge even without lifting something particularly heavy. Just hold an item weighing a few pounds with your arm fully extended in front of you. Within minutes (or even seconds in some cases), the weight seems to increase and the strain to keep the item elevated can become unbearable.
The inescapable physics of lifting heavy items is why companies must implement engineering controls that modify or eliminate the physical hazards of specific tasks. Defined procedures, worker behavioral coaching, and new-employee training are all important and helpful, but they can fail to protect workers if they aren’t used in conjunction with changes to workspaces and tasks.
And simple up-and-down movements are the easiest lifting tasks assigned to workers. Lifting from awkward postures (like reaching inside an enclosed space), twisting at the waist while lifting, and bending over during a lift can be even more damaging to the body, including by increasing spinal disc compression.
Then, there is physical fatigue. If you have ever helped someone move a heavy object, like a couch, that you must hold for an extended period, you are probably familiar with the fact that muscles have limits. You may have found yourself rapidly approaching the point where you were simply going to have to release your grip because your wrist and forearm muscles were no longer able to contract.
That dynamic can play out over the course of a worker’s shift. A lift they could make relatively easily when they arrived at work might be nearly impossible eight hours later. At that point, each execution of the task puts both the person and the product at risk.
What Factors Determine When a Load Surpasses Human Biomechanical Capacity?
It is important to understand that official guidance on manual lifting actions is based on relatively low-weight, low-risk lifts executed close to the body. Heavy objects and lifts conducted outside of the so-called power zone (or golden zone) change the calculus immediately.
Maximum safe lifting thresholds drop dramatically when a lift takes place below where a person’s hands are at rest at their side or above their shoulders. Experts in workplace ergonomics assess where a lift begins, where it ends, and how long the employee must sustain the lift — not just the weight of the object.
If a task exceeds human lifting capacity (or is likely to at any point in a worker’s shift) based on its weight, but the item is compact and will remain stable during a lifting action, a device like a hydraulic scissor cart might be sufficient. However, if the item’s weight exceeds set limits and it requires mid-lift maneuvering, an industrial manipulator, which can essentially create a zero-gravity environment from the employee’s perspective, might be necessary to ensure worker safety and avoid product damage.
How Does the Center of Gravity Affect the Lifting of Heavy Objects?
When an item has unevenly distributed mass, lifting it can shift its rotational torque to the worker’s back, forcing the stabilizing muscles to contract vigorously to counteract the unexpected twisting forces. Liquids in containers, sacks of loose material, and components with off-center balance points are good examples. Lifting them creates unpredictable dynamic shifts during the movement.
Unsurprisingly, standard lifting instructions are of limited use when a part’s visual center doesn’t align with its physical center of gravity. Using hoists or slings to move these types of objects can be helpful to a degree, but those approaches may allow an item to swing unpredictably. Industrial manipulators, on the other hand, can counterbalance off-center masses to ensure safe, smooth, and predictable movements.
The Hidden Hazard of Awkward Holds
A worker’s ability to lift an item isn’t solely about the upward force they can exert on it. If they can’t get a good grip on the piece, the safety of the lift is compromised.
Additionally, poor handholds on awkward or slick items require workers to apply excessive force with the muscles of their hands, wrists, and forearms. As a result, manually handling items without adequate grip points quickly leads to muscle fatigue that increases the risk of physical injury and property damage from dropped or mishandled items.
Equipment like slip-resistant gloves, simple suction handles, and manual carrying clamps can help, but only to a point. A safer alternative is the use of lift-assist systems with vacuum suction cups, pneumatic clamps, and other specialized end effectors that can apply the necessary grip force consistently, repeatedly, without ever tiring.
How Do Reaching and Travel Distance Affect Lifting Tasks?
As noted above, an object held away from the body has the effect of a lever arm, exerting significant force on a worker’s spine. As a result, repeatedly reaching into bins or shipping containers can take more of a toll on worker health than it might seem to at a glance. Combine that movement with torso rotation, and you have one of the highest-risk activities in manufacturing environments.
Various types of lifts and container positioners can help reduce the need for these movements, but often they don’t provide complete protection from back strain. What is needed in many scenarios are the articulated arms of an industrial manipulator.
When these systems are properly implemented, an operator can use them to reach into the deepest recesses of a container to retrieve an item with no leaning, reaching, or excessive physical stress. The worker’s role is simply to guide the end effector to the object, letting the device do the literal heavy lifting.
Understanding Muscle Chemistry and Fatigue
As we get worn out by a repeated physical task, we often think we just need to “muster the strength” for the next lift. However, that strength isn’t a state of mind but rather a function of how muscles work. Over time, activity depletes muscle glycogen and produces metabolic waste. These aren’t conditions you can simply overcome with willpower.
In fact, when a work tempo is too high, even relatively light items can become difficult to manage due to the worker’s muscles simply not being able to generate enough force until they have had time to recover. Scheduled pauses and rotating workers to stations with different physical demands can help keep them productive longer, but fatigue still comes into play eventually.
Industrial manipulators don’t have to contend with muscle fatigue, nor do the workers operating them. Implementing lift-assist solutions enables increased cycle velocity while simultaneously lowering fatigue and injury risk for workers.
Why Team Lifts and Other Workarounds Are Problematic
Coordinated two-person lifts might seem like a good solution for managing heavy objects, but they rarely distribute the weight evenly. As a result, one worker is forced into higher physical exertion, accelerating their fatigue. Height differences, mismatched cadence, and poor line of sight between partners introduce other challenges. Additionally, requiring two people to collaborate on certain lifts means the second person isn’t being productive elsewhere.
Informal workarounds — such as dragging parts on cardboard, pushing heavy crates along the floor, or balancing stock on rolling carts — might also seem like good solutions, but they rarely are. All these risks and ineffective or dangerous practices can be eliminated with pneumatic lift-assist equipment that makes difficult lifts essentially effortless.
The Heavy-Lift Decision Framework: Provide Training, Deploy Basic Aids, or Integrate Custom Lift-Assist Solutions
Challenging lifts can be addressed in three primary ways. Companies can provide task-specific training, equip team members with simple lifting aids, or integrate custom lift-assist devices. However, it is essential to consider each task separately from the perspective of the six criteria covered above:
- Mass
- Balance or weight distribution
- Grip security
- Horizontal reach
- Frequency
- Necessity of team lifts
With those factors in mind, actions fall into one of three categories:
- Tasks passing all safety criteria are suitable for manual execution, supported by good body mechanics and training on safe lifting techniques.
- Tasks with basic challenges, such as moderate weight or minor grip issues, can be managed through training plus simple mechanical aids like specialized gloves or manual hoists.
- Tasks that fail across multiple criteria call for customized industrial manipulators.
Final Thoughts
Improving operational ergonomics not only improves worker safety but also can increase productivity. Whether the solution for a particular task is training, basic equipment, or the implementation of industrial manipulators, companies that take the appropriate action benefit from fewer lost worker hours and increased output.
To learn more about how we work closely with manufacturers to provide the heavy-lifting solutions they need, contact Dalmec today.
