A conveyor in action

Designing Safety into Conveyors

May 19, 2021
Prevention through Design (PtD) can lead to safer and more productive conveyors, as well as other factory floor equipment.

All new conveyors inevitably succumb to the punishing bulk handling environment and begin to slowly degrade. They will eventually require more time and labor for maintenance, and the time between outages will continually shrink as the costs of operations will climb. The ongoing degradation is also accompanied by higher risks of injuries or fatalities as workers are more often called on to clean and maintain the conveyors and to fabricate short-term fixes to long-term problems.

According to the U.S. Occupational Safety and Health Administration (OSHA), for example, the highest prevalence of accidents involving conveyors are near where cleaning and maintenance activities most frequently take place—namely, the take-up pulley, tail pulley and head pulley.

Total replacements are cost-prohibitive, so to remain compliant and meet ever-increasing production demands, companies must make unavoidable upgrades and repairs.

Improving efficiency and reducing risks associated with conveyors can be done by using a hierarchy of control methods for alleviating hazards. The consensus among safety professionals is that the most effective way to mitigate risks is to design hazards out of the component or system. This usually requires a greater initial capital investment during development than short-term fixes will cost, but it delivers more cost-effective and durable equipment.

Hierarchy of Controls

Engineers should be forward-thinking, designing products that exceed compliance standards and enhance the customer’s ability to make upgrades cost-effectively and easily by taking a modular approach to design. Designing hazards out of conveyors entails alleviating hazards to improve safety.

But the methods used to protect workers can vary. In many cases, more than one control method might be needed and they might be lower-ranked controls. However, lower-ranked approaches are best considered as support measures rather than solutions in and of themselves.

As the above graphic illustrates, there are several controls available.

Personal protection equipment (PPE) provided and mandated by company management for people working around dangerous equipment can include respirators, safety goggles, blast shields, hard hats, hearing protectors, gloves, face shields and footwear. They provide a barrier between wearers and hazards.

Unfortunately, they can also be improperly worn and uncomfortable to use through an entire shift. It’s also difficult to know if they are being properly used, and they can offer a false sense of security. And most importantly, they don’t address the source of the problem.

Administrative controls (changing how people work) create policies that signal a commitment to safety, but written guidelines can be easily shelved and forgotten. Administrative controls can be taken a step further by establishing “active” procedures that minimize the risks. For example, supervisors can schedule shifts that limit exposure and require more training for personnel, but these positive steps still do not remove the exposure or the causes of hazards.

Warning signs are generally required by law, so using them is more of a compliance issue rather than a new way to reduce accidents in the workplace. Signs should be posted in plain sight, be clear and simple, and be washed when dirty or replaced when faded. Like most lower-tier controls, however, signs are easily ignored and do not remove the hazard.

Engineering controls that allow remote monitoring and control of equipment and guards, such as gates and inspection doors that obstruct access, greatly reduce exposure to risks. But again, they do not remove the hazard.

The substitute method replaces equipment or processes that create hazards with equipment or changes in material or processes that eliminate the hazard. For example, manual clearing of a clogged hopper could be replaced by installing remotely triggered air cannons.

Prevention through design (PtD) using hazard identification and risk-assessment methods early in the design process lets engineers create the safest, most-efficient conveyor or other equipment for the space, budget and application. In the example of the clogged hooper for example, PtD reduces the risks by calling for taller and tightly sealed loading chutes that control dust and spills, or heavy-duty primary and secondary cleaners to minimize carryback.

Analyzing PtD

The U.S. Centers for Disease Control (CDC), the organization that spearheaded the PtD initiative, points out that although underlying causes vary, studies of workplace accidents implicate design in 37% of job-related fatalities.

Cost is most often the main hurdle in using PtD retroactively, which is why it’s best to implement PtD in the planning and initial construction stages of product development rather than retrofitting equipment later. The cost of PtD initiatives after initial construction can be three to five times as much as when the improvement is incorporated in the design stage.

The biggest source of expensive retroactive improvements is cutting corners initially by seeking lowest-bid contracts. And the added engineering cost of PtD during the design phase is often less than an additional 10% of engineering, but has enormous benefits in added safety and increased productivity.

The low-bid approach is usually an implied rule baked into a company’s culture. It encourages bidders to design conveyors based on getting the maximum load on the conveyor belt and just barely meeting regulations using the lowest price materials, components and manufacturing processes available.

But when companies take the lowest-purchase-price approach, the benefits are often short-lived, and costs increase over time, eventually resulting in losses. In contrast, when purchases are made based on lowest long-term costs (life-cycle cost), benefits usually continue to accrue and costs are lower, resulting in a net savings over time.

Design Hierarchy

Rather than meeting minimum compliance standards, conveyors should exceed all code, safety and regulatory requirements using global best practices. By designing the conveyor to minimize risks and be  protected against the workplace environment (dirt, dust and debris), the workplace becomes safer and the equipment easier to maintain.

Life cycle costing should play into all equipment and component design decisions. Engineers should also anticipate that upgrades will eventually need to be made as technology, innovations and regulations push companies to add components to the conveyors and machines they are designing today. This can be done by designing the basic configuration of the conveyor to be modular—making it easy to add improved components or sections, as well as to remove obsolete ones, without increasing the structural steel requirements or significantly increasing the overall price.

The “Evolved Basic Conveyor”

Using the Hierarchy of Controls along with the Design Hierarchy, engineers can construct an “Evolved Basic Conveyor” that meets the needs of modern production and safety demands. An Evolved Basic Conveyor is a standard bulk material handling conveyor designed to allow easy retrofitting of new components that improve operation and safety, solving or preventing common maintenance problems.

Installing or providing for maintenance-minded components in the loading zone can greatly improve safety and reduce downtime. These components include slide-in/slide-out idlers, impact cradles and support cradles. On larger conveyors, maintenance aids such as overhead monorails or jib cranes assist in moving and replacing components.

Engineers should also ensure the conveyor has adequate access to utilities, typically electricity and/or compressed air, to facilitate maintenance and performance. Next-generation conveyor designs may even have specially engineered idlers capped with an independent power generator that would that use the conveyor’s movement to generate power for a wide array of autonomous equipment.

On conveyors, dust, spills and belt tracking are top concerns for many safety professionals. Field tests have shown that enlarged skirtboards and engineered settling zones promote dust settling and reduce fugitive material (i.e., material that escapes the conveyor and ends up in the surrounding area). Curved loading and discharge chutes control cargo transfer for centered placement and less turbulence. As the load is centered on the belt, guides ensure even travel through the take up for consistent belt tracking.

Any transfer point is prone to buildup and clogging if conditions such as humidity, material wetness, volume or surface grade is right. Flow aids such as vibrators or air cannons on chutes can keep material moving, extend conveyor life and reduce the safety hazards associated with manually clearing clogs.

Engineering safer conveyors is a long-term strategy. But by encouraging the use of the Hierarchy of Controls at the planning stage, along with the Design Hierarchy at the design stage, the resulting conveyor or other machine will likely meet the demands of modern production and safety regulations. The end results will be a longer operational life, fewer stops and lower operational costs.

Todd Swinderman is CEO emeritus of Martin Engineering.

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