Monday 24th Jan, 2022

The science and art of designing safer conveyors

Engineers from Martin Engineering explain how combining a mixture of hierarchies can lead to safer, more efficient conveyors.

New conveyor systems will inevitably succumb to the punishing bulk handling environment and begin the slow process of degradation. 

The system will eventually require more time and labour for maintenance, shorter spans of time will pass between outages, downtime periods will become longer, and the cost of operation will continue to grow. 

The chance of injury or fatality increases as well, as workers are further exposed to the equipment to perform cleaning, maintenance and to fabricate short-term fixes to long-term problems.

When examining the safety of a system, improving efficiency and reducing risk can be achieved through a hierarchy of control methods for alleviating hazards. One of the most effective ways to mitigate risks is to design the hazard out of the component or system. This usually requires a greater initial capital investment than short-term fixes, but can yield more cost-effective and durable results.

The science: hierarchy of control methods

Designs should be forward-thinking, exceeding compliance standards and enhancing operators’ ability to incorporate future upgrades cost-effectively and easily by taking a modular approach. 

In many cases, it will be necessary to use more than one control method, by incorporating lower ranked controls. However, these lower-ranking approaches are best considered as support measures, rather than solutions in and of themselves. 

PPE includes respirators, safety goggles, blast shields, hard hats, hearing protectors, gloves, face shields and footwear, providing a barrier between the wearer and the hazard. They can be worn improperly, may be uncomfortable to use through an entire shift, can be difficult to monitor and offer a false sense of security. But the bottom line is that they do not address the source of the problem.

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Administrative controls (changes to the way people work) create policy that articulates a commitment to safety, but written guidelines can be easily shelved and forgotten. Establishing ‘active’ procedures can take these controls a step further. 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 and causes of hazards.

Warning signage is generally required by law, so this is less of a method than a compliance issue.

Installing systems such as engineering controls that allow remote monitoring and control of equipment – or guards such as gates and inspection doors that obstruct access – greatly reduce exposure, but do not remove the hazard. 

Using the substitute method replaces something that produces a hazard. For example, manual clearing of a clogged hopper could be replaced by installing remotely triggered air cannons.

Examples of eliminate by design are longer, taller and tightly sealed loading chutes to control dust and spillage or heavy-duty primary and secondary cleaners to minimise carry back. Engineers can use hazard identification and risk-assessment methods early in the design process to create the safest, most efficient system for the space, budget and application. 

Low-bid process and life cycle cost

Although the policy is generally not explicitly stated by companies, the Low-Bid Process is usually an implied rule that is baked into a company’s culture. It encourages bidders to follow a belt conveyor design methodology that is based on getting the maximum load on the conveyor belt and the minimum compliance with regulations using the lowest price materials, components and manufacturing processes available.

But when companies buy on price, 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 cost (life-cycle cost), benefits usually continue to accrue and costs are lower, resulting in a net savings over time.

The art: design hierarchy

Life cycle costing should play into all component decisions. Buying on Life Cycle Cost and anticipating the future use of problem-solving components in the basic configuration of the conveyor provides improved safety and access, without increasing the structural steel requirements or significantly increasing the overall price. It also raises the possibility for easier system upgrades in the future.

Using the hierarchy of controls along with the design hierarchy, engineers will be able to construct an ‘evolved basic conveyor’ that meets the needs of modern production and safety demands. Built competitively with a few modifications in critical areas, 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 maintenance solutions in the loading zone can greatly improve safety and reduce man-hours and 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 the movement and replacement of components. Designers should ensure adequate access to utilities – typically electricity or compressed air – to facilitate maintenance and performance.

Dust, spillage 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. Curved loading and discharge chutes control the cargo transfer for centred placement and reduced turbulence. As the load is centred on the belt, guides ensure even travel through the take up to promote consistent belt tracking.

Any transfer point is prone to build-up and clogging under the right conditions. Flow aids such as vibrators or air cannons on chutes can sustain material movement, improve equipment life and reduced the safety hazards associated with manually clearing clogs.

Although design absorbs less than 10 percent of the total budget of a project, additional upfront engineering and applying a life cycle-cost methodology to the selection and purchase of conveyor components proves beneficial.

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