Todd Swinderman, Martin Engineering, discusses the methods that can be used in the planning, design and installation stages of a conveyor system to alleviate workplace hazards and extend the life of the conveyor itself.
All 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 between outages, longer periods of downtime and an ever-increasing cost of operation. This period is also accompanied by an increased chance of injury or fatality as workers are progressively exposed to the equipment to perform cleaning, maintenance and to fabricate short-term fixes to long-term problems. A total system replacement is cost prohibitive, but to remain compliant and/or meet ever-increasing production demands, upgrades and repairs are unavoidable.
To reduce hazards in the workplace, operators employ a variety of methods, from requiring the use of personal protective equipment (PPE) to installing the latest and safest equipment designs. When examining the safety of a system, improving efficiency and reducing risk can be achieved by utilising 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 the hazard out of the component or system. This usually requires a greater initial capital investment than short-term fixes, but yields more cost-effective and durable results.
The science: Hierarchy of control methods
Examining the US Occupational Safety and Health Administration (OSHA) accident database reveals the dangers of working around conveyors.1 Studies have revealed that accidents are most likely to occur near locations where cleaning and maintenance activities most frequently take place – the takeup pulley, tail pulley and head pulley.
Experienced engineers often recommend that operators retain an outside firm to examine system requirements and design new equipment around historical issues and specific needs of the application, with an overall objective of safety. Before the drafting phase, designers should establish the goals of reducing injuries and exposure to hazards (dust, spillage, etc.) to increase conveyor uptime and productivity, and seek more effective approaches to ongoing operating and maintenance challenges. Designs should be forward-thinking, exceeding compliance standards and enhancing operators’ abilities to incorporate future upgrades cost-effectively and easily by taking a modular approach.
Designing hazards out of the system means alleviating causes with the intent to bolster safety on a conveyor system, but the methods of protecting workers can vary greatly. 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. The downsides are that 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.
Administrative controls (changes to the way people work) create policies that articulate a commitment to safety, but written guidelines can be easily shelved and forgotten. These controls can be taken a step further by establishing ‘active’ procedures to minimise 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 and causes of hazards.
Warning signage is generally required by law, so this is less of a method than a compliance issue. It should be posted in plain sight, clearly understood and washed when dirty or replaced when faded. Like most lower-tier methods, signs do not remove the hazard and are easily ignored.
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 again, do not remove the hazard. Some operators go as far as installing interlocking guards connected to switches to discourage removal or proximity sensors to detect workers who break the safety plane of the conveyor.
Using the substitute method replaces something that produces a hazard with a piece of equipment or change in material that eliminates the hazard. For example, the process of manually clearing of a clogged hopper could be replaced by installing remotely triggered air cannons. However, operators may find that this method is not a practical solution for all belt conveyor systems. In most cases, it is difficult to achieve the same volume of throughput when replacing a belt conveyor with another type of system, such as an enclosed pipe conveyor.
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 carryback. By using hazard identification and risk-assessment methods early in the design process, engineers can create the safest, most efficient system for the space, budget and application. These designs alleviate several workplace hazards, while minimising cleanup and maintenance, reducing unscheduled downtime and extending the life of the belt and the system itself.
Economic analysis of prevention through design (PtD)
Another way of saying ‘eliminate by design’ is PtD (prevention through design), the term used by The National Institute of Occupational Safety and Health (NIOSH). As a department of the US Centers for Disease Control (CDC), the organisation spearheaded the PtD initiative.3 In its report, the institute points out that, while the underlying causes vary, studies of workplace accidents implicate ‘system design’ in 37% of job-related fatalities.
Although injuries are the focus of the NIOSH report, the prevention aspect of design also greatly impacts production. In most cases, workplace hazards produce consequences such as downtime, product loss and reduced efficiency from spillage, dust and early equipment failure. The cost of operation is dramatically influenced by the efficiency of the system, but is unique to each application. Cost is most often the main inhibitor to PtD, which is why it is best to implement safer designs in the planning and initial construction stages, rather than retrofitting the system later. The added engineering cost of PtD is often less than an additional 10% of engineering but has enormous benefits in improved safety and increased productivity.
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. Retroactive improvements can cost far more, and are sometimes impossible due to designed-in restrictions or space limitations. This cost of retroactive improvements is reduced by implementing modular designs with plenty of space to work and expand. The biggest cause of expensive retroactive improvements is cutting corners initially by seeking lowest-bid contracts.
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.
Maximising the volume of cargo and minimising the price of the system usually means choosing the narrowest feasible belt operating at the highest speed possible. This leaves little margin for error and in many cases results in chute plugging, excessive spillage and reduced equipment life.
According to conveyor expert and P.E., Todd Swinderman, “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 saving over time.”4
The art: Design hierarchy
To safely maximise production, designers and engineers are urged to approach the project with a specific set of priorities. Rather than meeting minimum compliance standards, the conveyor system should exceed all code, safety and regulatory requirements using global best practices. By designing the system to minimise risk and the escape and accumulation of fugitive material, the workplace is made safer and the equipment is easier to maintain.
Life cycle costing should play into all component decisions. Be aware of specifications on project components that state ‘specific manufacturer name/or equal.’ Vaguely written ‘or equal’ specifications are there for competitive reasons and allow contractors to purchase on price without adequate consideration for construction or performance. Rather, buying on ‘life cycle cost’ or ‘engineer-approved or equal’ 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. The ability to accommodate future increases in capacity can be included in the original design, expanding options and reducing future modification costs.
1. Conveyor Accident Database, OSHA, US Dept. of Labor. Washington, DC. (2018), https://www.osha.gov/pls/imis/AccidentSearch.search?acc_keyword=%22Conveyor%20Belt%22&keyword_list=on
2. ‘Foundations for Conveyor Safety’, Ch. 31, pp. 404 – 440, Martin Engineering, Worzalla Publishing Company, Stevens Point, Wisconsin, (2016), https://www.martin-eng.com/content/product/690/safety-book
3. HOWARD, J, M.D., ‘Prevention through Design: Plan for the National Initiative’, National Institute of Occupational Safety and Health (NIOSH), U.S. Centers for Disease Control (CDC), Department Of Health And Human Services. Washington, DC. (2010). https://www.cdc.gov/niosh/docs/2011-121/pdfs/2011-121.pdf
4. SWINDERMAN, R. T., ‘The Economics of Workplace Safety: Putting a price on material handling mishaps’, Coal Age, Vol. 123, No. 3, pp. 28 – 31, April, (2018). https://www.coalage.com/features/the-economics-of-workplace-safety/
Read the article online at: https://www.worldcement.com/special-reports/22072020/playing-it-safe/