Physical overexertion is the leading cause of the most serious nonfatal injuries and illnesses involving days away from work, according to the Workplace Safety Index (Liberty Mutual, 2008). Because warehouses and distribution center (DC) operations have an abundance of ergonomic challenges, and because peak order fulfillment periods tend to exacerbate these issues, warehouse workers are among the top three highest-risk occupations for sprains, strains and low back disorders. These findings make a compelling business case for companies to systematically address the root causes of ergonomic issues in the workplace.
Most Common Injury Instigators
- Product storage heights that are too low or too high.
- Retrieving products from the floor, elevated shelving, inside truck trailers, or from underneath storage racks increases a worker's risk of overexertion due to torso bending/twisting and awkward upper extremity positions.
- Poorly-designed packing and sorting workstations. Work benches and workstations often require extended reaches to access packaging material or products along conveyors. These workstations often lack adjustability and require prolonged sitting or standing in awkward postures that increase ergonomic risk factors, such as back bending and extended reaches.
- Poor flow management of goods through the warehouse. Lean principles are applied throughout most organizations but they are not always seamlessly integrated with ergonomics. Examples of this include using partial, double, or triple slotting storage techniques to maximize shelving space so that the greatest amount of product can fit in the smallest amount of warehouse space. This type of slotting can increase ergonomic risk factors such as bending and elevated reaches. In addition, workers may bend at the torso to reach under low racking, or they may be required to forcefully pull out containers from under product stacks to access the appropriate item needed for order fulfillment.
- Excessive walking while navigating narrow and congested aisles. Modern warehouses are larger than ever before and the majority of workers' time is spent in travel. Narrow width and congested aisles can add to this labor intensive activity, requiring order pickers to stop farther from the designated pick slot and carry items longer distances to pallets or carts. This can lead to employees overloading themselves by carrying multiple parcels around obstacles to limit the number of trips.
Fit Work to Worker
As a practicing ergonomist who has spent a lot of time in this tough environment, the common trends I have seen driving the increase in ergonomic concerns are those listed above. However, these trends do not have to gain popularity. Adhering to one ergonomic principle can not only reduce injuries and illness in the workplace but can lower workers' compensation costs and improve worker morale and productivity.
The primary principle of ergonomics is to fit the job to the physical and cognitive capabilities of the worker. Proper ergonomic applications in warehouse and DC environments can translate into a safer and more efficient workplace. Some of the factors influencing companies to consider ergonomic improvements include the following:
- The relentless push to do more with less;
- Offering a higher number of stock keeping units (SKUs) that may include vastly different product sizes and storage requirements;
- More consolidated DC networks (e.g., fewer buildings) using larger footprint (e.g., 1 million square feet) all-in-one facilities that include single line orders, multiple line orders, unit loads, bulky non-conveyable orders, and individualized value-added services like gift wrapping;
- Shifts in peak processing periods driven by an increase in e-commerce order fulfillment and through post-holiday redemption of gift cards;
- An increasing number of older workers, those aged 55 years and older, in the workforce with a significant increase of female employees between the ages of 65 and 74.
Simple changes can be implemented to assist even the most cost-conscious and conventional organizations that have minimal plans for expansion.
Three Top Tips
1. Improve Storage and Product Access
An ergonomic principle frequently shared with warehouse employees is the adage, "If you cannot shake hands with your work, it is unfriendly." The best method to keep warehouse work user-friendly is to position SKU access to high frequency items inside the "handshake zone" (heights from 37" to 47", within 16" from your body). Here are some of the current best practices for keeping warehouse work friendly and efficient:
- Use single slotting for the most frequently handled items and optimize access within the comfort zone (24" to 62" work heights) and ideally in the handshake zone.
- Ensure that employees have access to at least three sides of a pallet, if feasible. Emphasize this point with fork lift drivers who move pallets in and out of slots. Pallets that are too close in proximity may not give employees enough clearance to easily reach the items at the rear. Therefore, extended reach postures, or stepping onto or around pallets, to retrieve product is necessary. This method increases the likelihood of potential slip/trip and fall injuries.
- Train employees to use pyramid de-palletizing techniques rather than layer picking to minimize extended reaching.
- Use drawer-style racks or pallet dollies to slide the bottom rows of pallets out to bring work closer to the employee.
- Raise work heights through methods such as raised bottom shelving, adding sacrificial pallets under loads, or raising the forks on powered industrial trucks to improve load access.
- Use gravity-fed flow racks to reduce the space consumed for slower moving products.
- Use load leveling carts and rolling canvas totes with spring bottoms to keep loads at handshake height.
- Consider high lift (>30") pallet jacks to be used as portable lift tables.
- Use low-profile pallet turntables for high volume pick areas; scissor lifts are most useful and typically cost-justified for the highest-moving products.
- Consider lighter weight plastic pallets and use a pallet dispenser to limit manual handling.
2. Provide Ergonomic Warehouse Workstations
- Today's packing or order processing workstation or workbench is frequently intertwined with the overall warehouse system, and the equipment, materials, and supplies storage need to coincide with the flow of the work.
- Provide adjustable height stations to accommodate different sizes of operators. Be sure to provide preferred reference marks for employees to easily and consistently position tables.
- Store knock down flat product supplies vertically, like library books, instead of flat, like folded laundry.
- Mount peripherals such as keyboards, HMI screens, taping, or packing material on adjustable arms to unclutter the worksurface.
- Use box edge flaps to improve access and reduce awkward upper extremity positions.
- Use tilt stands to improve loading access.
- Provide anti-fatigue matting and foot rails for standing operations to reduce static loading.
- Use LED lighting to improve the visual environment.
- Use conveyor-mounted deflect bars to move product close to the side edges to reduce reaching.
3. Optimize warehouse layout and order picking equipment
- Integrate ergonomics with warehouse management systems (WMS) so that optimal slotting can be done based on container characteristics such as weight, size, and throughput.
Additional recommendations include the following:
- Review the warehouse and DC slot-management system to optimize the flow of goods through the warehouse and to ensure that pallets are placed in full slots according to case weight and movement speed of the product.
- Increase the width of aisles where fast-moving product is located. This will allow pallet jacks to get closer and will reduce the distance the loads must be carried.
- Stagger the start times for employees at the beginning of the day so that fewer workers access the same slots at the same time. Small start time differentials can provide adequate spacing for sufficient disbursal during order picking.
- Use a preventive maintenance program for existing pallet jacks and carts. This requires periodically checking the working components of all pallet jacks and carts so they are kept in good condition and within the push and pull requirements.
- Consider vertical carousel lifts or systems that use the "goods-to-person" principle to eliminate walking times.
- Provide intelligent assist devices; these computer controlled devices enable employees to lift, move, and position loads more quickly and intuitively.
- Build in ergonomic criteria, such as rotating and vibration reducing seats and high visibility masts, into the purchase or lease specifications for powered industrial trucks.
The Future Warehouse and DC
Technology and different warehouse layout options are making it easier for companies to design their space to overcome ergonomic challenges. WMS improvements, such as pick-to-light, pick-to-voice, or even pick-to-feel systems, can minimize walking distances, reduce errors, and reduce multiple handling.
Also consider alternative warehouse floor plan designs, depending on the product and delivery methods. Innovative layouts, such as the Flying V, Fishbone, or Chevron, reduce dual-command travel by almost 10%, when compared to a traditional warehouse with a middle cross aisle, and by up to 15.5% when compared to a traditional warehouse without a middle aisle (Gue and Meller, 2008).
These are just a few potential ergonomic improvements for warehouse/distribution centers. When you take an objective, quantitative look at this environment, you will see that there are opportunities, and that you can indeed make a difference.
Josh Kerst, CPE, CIE, is an ergonomist and vice president with Humantech, Inc., an ergonomics consulting firm in Ann Arbor, Michigan.