In the workplace, we can view manual materials handling (MMH) as any process in which the human operator is asked or required to lift, lower, push, pull, carry or perform any other similar task in which an object is moved through space solely under the power of the human operator. Additionally, some assisted activities such as pushing a cart or using a mechanical assist still may be viewed as a manual materials handling task.
Many in the work force view materials handling tasks as only those tasks that involve weights that are perceived as heavy. In truth, MMH involves any handling of a product, whether it is a pencil or a 70-pound piece of electronics equipment. MMH is not relegated solely to heavy manufacturing environments; it includes jobs in a plant where a person has to lift a 1-pound component and jobs in an office where a person must lift a 55-pound computer monitor.
Is MMH a Health and Safety Risk?
Manual materials handling is a known risk in industry period. There should be no argument. More than enough data is readily available to prove this point. When looking at injury and illness statistics, musculoskeletal disorders related to MMH seem to fall into several categories:
Accident Worker loses balance or control of the load and gets injured, often in the form of a muscle strain;
Overexertion Worker attempts to lift a heavy load or conditions of a lift have high physical demands (e.g., task requires awkward handling or extreme postures);
Fatigue induced High frequency handling of a load that is within a worker's capability begins to "wear down" the body and yields an injury (the cumulative trauma model).
Realizing that these different situations exist, a review of current injury data gives us insight into the impact of MMH-related incidents. In 2003, there were approximately 340,000 overexertion injuries, with 185,000 being specifically associated with lifting (Bureau of Labor Statistics). According to Liberty Mutual, the cost of overexertion injuries reached almost $13.2 billion in 2002. This cost has increased 16.4 percent from 1998 to 2002. Of course, all overexertion injuries may not be directly related to MMH, but given the nature of this injury, it is a safe assumption that a significant percentage are a result of the high forces required in MMH tasks. Therefore, it should be safe to say that MMH is a known risk.
Reducing the Risk of MMH
The first step in addressing MMH in a facility is to admit that there is a problem manual materials handling is a risk that requires a resolution. The second step is to look at MMH from a slightly different perspective, as simply a part of the business that needs to be designed for safety, efficiency and productivity. Instead of running straight to the NIOSH lifting equation or the Liberty Mutual tables, a common risk-based approach in ergonomics, adopt the goal to eliminate MMH whenever possible simply because it is a risk.
Does the load need to be moved at all?
The first question that should be addressed when evaluating a MMH process is whether the load needs to be moved at all. Sometimes the most important question to ask is, "Why are we doing this?" If there is no specific value to moving a load, then don't do it. If unnecessary tasks can be eliminated, risk can be reduced and efficiency can be gained.
Is there unnecessary duplication in the movement of materials?
This second question can have the exact same impact on the process. Unnecessary handling of loads, re-handling of loads and duplication of processes are clear signs of a wasteful system. Achieving a direct line of flow for a load will reduce the number of times it is handled, resulting in reductions in damage to loads from frequent handling, reduction in risk to employees and, once again, improved efficiency in the process.
Therefore, if a process is simply evaluated to ensure there is a well-planned, efficient movement of loads, ergonomics benefits will already be realized.
Ergonomics Risk Assessment of MMH
It is at this point in the process that a risk assessment of the task will help to determine the level of need (i.e. cost) for the solution. There are three main methods of risk assessment that are readily available for health and safety professionals to use: NIOSH Lifting Equation (NLE), Liberty Mutual Tables (LMT) and the University of Michigan Energy Expenditure Prediction (EEEP) model. (Resources for obtaining these tools, including some instructions, are: Application Manual for the NIOSH Lifting Equation www.cdc.gov/niosh/94-110.html; Liberty Mutual Tables for MMH libertymmhtables.libertymutual.com/CM_LMTablesWeb/taskSelection.do?action=initTaskSelection; University of South Florida Online MMH Analysis Tools www.hsc.usf.edu/tbernard/ergotools.) Before using any of these tools, it is highly recommended that the analyst receive some training and be aware of the tools' strengths and weaknesses, and the type of information they can provide.
The goal of the risk assessment is to understand how dangerous the MMH task may be. Each of the MMH risk assessment tools has been found to perform better in different circumstances, which can provide a guide to choosing the best tool for a task. If the MMH task is lifting, the choice between risk assessment tools can be based on the frequency of lifting. The NLE can be used for any frequency, but it works best for low frequency (<=3 lifts per minute) tasks. For moderate frequency tasks (3 to 5 lifts/minute), the LMT provides the best information. For high frequency tasks, the EEEP is the best method to determine the potential for fatigue. To make this choice even simpler, especially because the EEEP model can be challenging when used correctly, if the frequency of lifting is >6 lifts/minute, the job is probably risky and an engineering control is warranted. If the MMH task is pushing, pulling or carrying, then the best tool will be the LMT.
Depending on the outcome of the risk assessment, the type of control can be determined and justified. Basically, the higher the risk, the greater the need for an engineering control. If the risk is severe enough (e.g., NIOSH lifting index >3; LMT population capable <10 percent), then a mechanical assist may be necessary. If the risk assessment produces results that are moderate, then the decision becomes a little more challenging.
Controlling the Risk
Once the level of risk is determined for the MMH task, the next step is to determine the best method of controlling the risk. The first two questions in the flowchart revolved primarily around engineering concerns and the efficiency of the system. The question of controlling the risk is a choice between engineering, work practice and administrative controls, which revolves around health and safety concerns and the economic feasibility of the solution.
Choosing between these solution options can be fairly easy if one simple question is answered "Do you have any money?" If the answer is NO, then engineering controls have to go. If you have a little money, then all the options are possible with some creativity, and if you have a lot of money, anything is possible. Of course, just because money is available does not mean that the most expensive solution should be chosen.
A good approach to use to help determine the best solution for the task is to perform "What if?" scenarios. By predicting the potential impact of a solution, the risk assessment tools can be used to determine the effect on risk. The key is to predict the type of changes that can be expected from the different solutions (e.g., lifting training vs. lift table). The solution that produces the greatest reduction in risk could be a winner.
A Guide to MMH Solutions
When trying to find a solution to reduce or eliminate the risk of manually handling a load, there are two viewpoints that can be used: 1) Look at the assist and see if it can perform the task; or 2) Look at the task and see what types of equipment will fit. Finding a MMH solution can be broken down into two simple questions:
1. What are you handling? (e.g., boxes, bags, sheets, etc.)
2. What are you doing with the load? (e.g., lifting, carrying, pushing, etc.)
Virtually every MMH solution can be determined by answering these two questions. Depending on the nature of the task, a different type of solution may be more appropriate than another. By understanding the strengths and weaknesses of the different controls that are available, finding a solution can be as easy as looking up the option in a table. Now, all that is needed is the table actually, it is just around the corner.
Cal/OSHA is currently working in partnership with NIOSH and the Material Handling Industry of America (MHIA) to develop an ergonomics guideline for manual material handling. This guideline will focus primarily on the solutions available for various MMH tasks and provide a guide to choosing and finding the best solutions. So, this article ends with something of a cliffhanger. The process is set to ensure efficiency of MMH tasks, determine risk of current tasks and establish the need for a control measure. The final choice of the control measure awaits a decision. The last piece of this puzzle will be available very soon from the above organizations free for all of us to use. Stay tuned to their Web sites (Ergonomics Guideline for MMH Cal/OSHA (page under construction) www.caloshareu.com/login1.html; NIOSH www.cdc.gov/niosh/topics/ergonomics; MHIA www.mhia.org) and look for future updates on the release of this guideline in Occupational Hazards' electronic newsletter Ergonomics News.
David M. Brodie, MS, CPE, is the director of Ergonomics Services for the Ergonomics Center of North Carolina. He is a contributing editor to the Ergonomics News e-newsletter. He can be reached at [email protected]