Search the web, and you’ll find plenty of content related to belt conveyor safety. Complete the same search for drag conveyors, however, and you’ll discover the dearth of information on this subject. Few resources are publicly available about drag conveyor safety. While there are many areas of overlap between these two conveyor types in respect to safety—practices like lock-out, tag-out always apply—differences between the systems mean drag conveyors come with a unique set of safety considerations and practices. Additional content on drag conveyor safety is therefore warranted.
The Design Phase
The best time to consider drag conveyor safety is before you purchase conveyors or contract a third-party entity to buy them on your behalf. By taking safety into account during the design phase of a project, you can identify conveyors that are safer than others and avoid risks you might otherwise take on. For example, we designed our SMART Conveyors™ with an enclosed box, which protects customers from contacting the chains, sprockets, and paddles. Many other drag conveyors are not enclosed, a design that comes with inherent risks. Employees can fall into the troughs, sever fingers in pinch points, or have objects fall on them over the sides of the conveyors.
|Safe Design Features on SMART Conveyors™|
Thought regarding conveyor safety must precede even the design phase if you purchase conveyors through an EPC contractor. Because you are not personally selecting the equipment, you must explicitly state your safety requirements in your specifications. It’s an unfortunate reality that the EPC model incentivizes engineering contractors to buy the cheapest equipment they can find that will satisfy the bid requirements, so if you have not explicitly stated you want conveyors that are “dust tight” and which are powered by shaft-mounted gearmotors, you should not expect your EPC to select equipment with these features. What’s more, if you’ve identified a manufacturer you trust to supply a safe conveyor, you should require products from that company in your specifications. When it comes to EPCs, you can’t expect anything more than you requested. Thus, if the company you trust charges more for its equipment than its competitors, your EPC is unlikely to purchase from the company if left to their discretion.
If you’re not confident enough in any one manufacturer to provide you with an inherently safe drag conveyor, consider requiring your EPC to procure systems that meet the following criteria:
- Compliance with NFPA codes for fire and explosion safety (NFPA 652 and 664)
- Evidence for the necessary box strength to withstand explosion overpressures (if an explosion risk exists, per NFPA 664)
- Plug detection
- Zero-speed detection
- Fully enclosed box (for sized materials)
- “Dust-tight” operation
- Conduit mounts (ensures technicians don’t weld onto the conveyors)
- Controls with emergency stops and alerts
- Electrical interlocks for overflow prevention
- Sealed inspection windows and doors
- Shaft-mounted, direct-drive gearmotors
- Quick-release deluge nozzles (if applicable, for easier and faster maintenance)
SMART Conveyors™ from Biomass Engineering & Equipment are fully enclosed, so the sprockets and chains are safely contained within the conveyor box. SMART Conveyors™ are inherently safer than most drag systems.
The design phase is also the right time to identify reliable conveyors and supplementary systems that limit downtime. The best way to protect employees around a drag conveyor is to reduce their time working on or around it, especially during unscheduled downtime. Mistakes are more likely to occur in a downtime situation than during routine maintenance due to the pressure on technicians to get the system up and running as quickly as possible. If a technician is ever going to take a shortcut, it’s most likely to happen during unscheduled downtime.
To prevent unscheduled downtime, project managers and other personnel who select or specify conveyors should consider their conveyors’ present and future capacity requirements. If there’s a reasonable expectation that volume will increase, managers should specify conveyors that can handle the future load. If they don’t and they attempt to use the original conveyor in an application for which it is undersized, the conveyor will wear rapidly and experience premature failures (i.e., unscheduled downtime).
Managers should also consider a conveyor’s historical maintenance demand, something they can accomplish by contacting companies that use or have used the conveyor. What the managers learn will allow them to project future maintenance costs and better quantify maintenance-related dangers. They can further reduce maintenance and unscheduled downtime by creating preventive maintenance schedules, writing procedures for proper use of the equipment, and installing any necessary screening systems.
Conveyor Safety Basics
Once you have a drag conveyor system, it doesn’t matter whether it’s inherently safer than other conveyors or not—you must take the precautions necessary to protect anyone working on or around the machines. The guide below contains many standards that apply to drag conveyors. Note that the list does not include every precaution you should take. You alone are responsible for your safety and for others at your plant. We recommend you work with an EHS specialist to create a substantive guide specific to your operation.
- DO NOT operate equipment with missing or defective safety devices.
- ENSURE overflow devices (electrical interlocks) are in place and operational.
- ENSURE the conveyor is equipped with operational zero-speed sensors.
- ENSURE the chutes leading to and from conveyors are fitted with appropriately placed, operational plug detectors.
- DO NOT stand or sit below unsecured chains.
- READ the machine’s manual before installing, operating, or maintaining it.
- DO NOT remove items that are stuck in a conveyor without first de-energizing and locking out the conveyor.
- DO NOT walk on conveyor covers.
- DO NOT climb the conveyors.
- BEWARE pinch points at the inlet, outlet, and other open sections.
- DO NOT stand over, sit on, or lean against explosion relief devices.
- Apply guards where necessary to protect personnel working around the conveyors (not applicable for SMART Conveyors™)
Left: Guards protect workers from the conveyor’s return chain, sprockets, and drive. Right: A conveyor (obscurred) operates without guards. Workers are exposed to the chain and multiple pinch points.
- ALWAYS use lock-out, tag-out procedures before working on a conveyor.
- CHECK with the manufacturer before performing modifications to the conveyor.
- NEVER weld anything to the conveyor box. The UHMW plastics, common in many drag conveyors, are flammable. SMART Conveyors™ use UHMW as wear liners. Burn injuries may occur if the liners catch fire.
- CHECK FOR and RELEASE tension in the chains before working on them.
- REPLACE panels that have been removed.
- ALWAYS CLOSE and LATCH access doors and inspection windows.
- DO NOT stick body parts into a conveyor without it first being de-energized and locked out.
- SECURE chains on inclined conveyors that could move while unpowered before working in the conveyor.
- CLEAN deluge nozzles at an interval to preserve their ability to function.
- INSTALL tails above ground level and/or provide enough room around the tail so maintenance technicians can easily access, maintain, and clean the machine.
Are you concerned with the safety of your conveyor systems? Contact us to discuss your material-handling application today.
PICTURED AT TOP An open drag-chain conveyor is inherently riskier than an enclosed conveyor. The conveyor pictured above lacks guards around the sprockets and has pinch points exposed between the paddles, the bed, and the driveshaft.