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Screw Conveyors: Hazardous Machinery Requires Specific Procedures

- December 7, 2018 by Glen O'Rourke, ALCM (View all posts by Glen)

Screw conveyors are used to convey bulk materials in granular form from one point in a process to another. They consist of a continuous helical blade about to a rotating shaft, (also referred to as an auger), enclosed within a trough or tube, powered by a motor and gearing system. They may be horizontal, inclined, or vertical. Screw conveyors are most commonly found in the agriculture, food processing, pharmaceutical, building materials (such as cement), metals processing, coal, lumber (for sawdust), and other industries.

The forces needed and produced by screw conveyors depend on a number of factors. These include the rotating speed of the auger; the density of the material being conveyed; and the friction produced by the material. Depending on the application, the forces produced can be tremendous. If a person working with or around a screw conveyor came in to contact with the rotational portion of the conveyor while it was in operation, that person could be subject to crushing injuries, with the most severe cases resulting in amputations and even death.

When Things Go Wrong
In the summer of 2017, at a foundry in Southern California, a screw conveyor system was in use as part of a dust collection/reclamation system. During simultaneous maintenance and cleaning operations, the electrical power to the screw conveyor was turned off. An employee was performing cleaning inside of the hopper that fed the conveyor and was in a position where his legs were in contact with the auger. After the maintenance operations were complete, another employee (who could not see the employee doing the cleaning) activated the machine by turning on the power. Once activated, the rotating auger grabbed ahold of the employee’s legs and pulled them in to the screw conveyor causing massive crushing injuries to both legs and pinning them inside. Emergency medical personnel were summoned, and it was determined that the employee could not be extracted without using extraordinary measures. A surgical team had to be brought in and both of the employees legs were amputated on site.

Another example occurred in the fall of 2013, at a winery in Northern California. A screw conveyor system was in use to move grapes from a collection hopper in to de-stemming and pressing machinery. An employee was performing cleaning operations inside this hopper when the power to the screw conveyor system was switched on inadvertently. The rotating auger grabbed ahold of the employee and pulled him in to the machinery causing crushing injuries to multiple body parts, resulting in a fatality.

What You Can Do to Prevent Injuries
In order to prevent injuries, certain control measures should be undertaken. These control measures include:

  • The screw conveyor system should be designed so (to the extent possible) the trough is completely enclosed such that people working in proximity cannot come in contact with the auger while it is rotating. Interlock switches can be used to ensure that the system shuts down automatically when any covering/access hatches are removed.
  • Systematic lockout/tagout procedures for the screw conveyor system should be developed and implemented. The procedures should be written and all employees effected (maintenance, cleaning, operators, others in proximity) should be trained in the procedures. Each employee performing maintenance, cleaning, or similar procedures, while exposed to the auger or other moving parts, should use his/her own lock to lock out the power. Thus the number of locks used equals the number of people performing cleaning/maintenance procedures.

Screw conveyors allow quick and efficient moving of bulk materials to perform a high volume of processing.  Such machinery can reduce exposure to severe injuries during maintenance, cleaning, and similar operations.  When proper hazard control procedures are established and practiced, injuries can be prevented.



KWS Manufacturing, Ltd.; Screw Conveyors Engineering Guide; 2015; Burelson, Texas

Yu, Yongqin; Theoretical Modeling & Experimental Investigation of the Performance of Screw Conveyors; 1997; University of Wollongong; New South Wales, Australia

Pasadenastarnews.com; August 28, 2017

KSBW.com; October 4, 2013