Conveyor System Safety

Last updated on May 31st, 2023 at 03:43 pm

Conveyor systems are everywhere, from the baggage handling systems in airports to people movers in airports and malls to package handling, mining, and general industrial applications.

Conveyor designs range from very small dual-belt conveyors used to move printed circuit boards through electronic board-stuffing machines to pneumatic conveyors moving pelletized plastic from storage silos to injection moulding machines to massive troughed-belt mining conveyors moving hundreds of tons of ore a minute.

In this article, I will cover the basic requirements for some of the common types of conveyors, and I’ll be referencing the most common conveyor standards and regulations in use today. I will exclude all applications that involve moving people as I want to focus on the specifics of material handling conveyors. I will also avoid underground mining conveyors because they have specific safety requirements related to the materials and environment in which they operate.

TL;DR

Conveyor systems are widely used in various industries for material handling purposes. They can be categorized into bulk material conveyors and package or unit handling conveyors, with numerous sub-types under each category.

Ensuring conveyor system safety is crucial to prevent accidents and injuries. Hazards associated with conveyors include entanglement, abrasion, crushing, and severing. Workers’ hands and fingers can get caught in a nip or shear point, especially during cleaning and maintenance tasks. Moving belts can cause abrasion injuries, and belt tensioning devices can create crushing hazards. Screw conveyors have entanglement and drawing-in hazards and shear points that pose finger and hand-severing hazards. Effective controls for conveyor safety include installing guards for moving parts, using warning signs or lights, ensuring openings are guarded when not in use, and providing emergency stop controls and interlocking devices. Crossovers, aisles, and passageways should have adequate clearance and guards. Conveyor controls should support lockout/tagout procedures. Emergency egress and accessibility of emergency stop buttons or pull cords are important considerations. These safety measures can help mitigate risks and protect workers in conveyor system operations.

Primary Sources

The primary standards sources related to conveyors used in this article include:

[1] Safety Standard for Conveyors and Related Equipment, ASME B20.1. 2018.

[2] Continuous handling equipment and systems — Safety and EMC requirements for mechanical handling of bulk materials except fixed belt conveyors, EN 618. European Committee for Standardization (CEN). 2002+A1:2010.

[3] Continuous handling equipment and systems — Safety and EMC requirements for equipment for mechanical handling of unit loads, EN 619. European Committee for Standardization (CEN). 2002 + A1:2010.

[4] Continuous material handling equipment and systems — Safety and EMC requirements for fixed belt conveyors for bulk materials, EN 620. European Committee for Standardization (CEN). 2002 + A1:2010

If you want to dig deeper, I’ve included a much more comprehensive bibliography at the end of this article.

Defining a Conveyor System

At its most basic, a conveyor system consists of a continuously moving surface that moves material from one location to another. Conveyors can be divided into two basic types: bulk material and package or unit handling. Bulk materials range from powders to crushed ores and other similar materials. Unit handling conveyors move material in bags, boxes, pallets, or similar methods to contain or group other materials into larger units for handling.

Within the two basic types of conveyors, there are many sub-types, including:

• Belt
• Trough
• Walled
• Belt Feeder
• Bucket
• Chain
• En Masse
• Flighted
• Horizontal reciprocating
• Vertical reciprocating
• Pneumatic (these have some special requirements)
• O-ring
• Powered and free roller
• and many more.

Some examples of different types of conveyors are shown in the photos below.

Conveyor system components

The diagram above comes from A User’s Guide to Conveyor Belt Safety, published by the CSST (now called the CNESST) and the IRRST in Montréal, Québec, Canada. This excellent guide was free for download in English from Ontario’s Workplace Safety & Prevention Services (WSPS). However, it was removed from their website in January 2021. The guide is available as a download at the bottom of this article. It is still available in French from IRRST. WorkSafe Alberta also adopted the guide, and I’ve also provided that document as a download at the bottom of this article.

Definitions

Let’s start by comparing the definitions of conveys used in the EU versus those used in the USA. I’ll start with the EN 620 [4] definition.

3.2

belt conveyor

conveyor including its structural components, using a moving belt with a continuous rubber or polymeric surface for the conveying medium. The belt is usually driven by a pulley at one end, passing over a free-running pulley at the other end. The upper portion of the belt may be supported by free-running idlers or suitable flat surfaces. The conveyor may be arranged for horizontal or inclined travel, the angle of slope depending on the character of the goods conveyed and the type of belt.

EN 620:2010 [2]

Here’s the US definition:

conveyor: a horizontal, inclined, or vertical device for moving or transporting bulk material, packages, or objects in a path predetermined by the design of the device and having points of loading and discharge, fixed or selective. Included are skip hoists and vertical reciprocating and inclined reciprocating conveyors. Typical exceptions are those devices known as industrial trucks, tractors, trailers, tiering machines (except pallet load tierers), cranes, hoists, power shovels, power scoops, bucket drag lines, trenchers, platform elevators designed to carry passengers or an operator, manlifts, moving walks, moving stairways (escalators), highway or railway vehicles, cableways, tramways, dumbwaiters, pneumatic conveyors, robots, or integral machine transfer devices.

ASME B20.1, 2012 [3]

The US standard has taken pains to include specific types of machines that share characteristics with conveyors and may be confused with them, while the EU standard has a more straightforward definition. The core of the two definitions is essentially the same, a moving surface used to move materials from here to there.

Hazards

There are a few common hazards present in every conveyor system:

• Entanglement (in-running nip between the belt and all pulleys and rollers, wire stitches at the belt join, the conveyed material, etc.)
• Entanglement in the drive system
• Abrasion from the moving belt
• Crushing in belt-tensioning devices and other parts of the mechanism
• Severing in screw conveyors

Many other hazards must be considered, but let’s look at these first.

Entanglement

Conveyor-related injuries typically involve a worker’s hands or fingers becoming caught in nip points or shear points on conveyors and may occur in these situations:

• Cleaning and maintaining a conveyor, especially when it is still operating.
• Reaching into an in-going nip point to remove debris or to free jammed material.
• Allowing a cleaning cloth or an employee’s clothing to get caught in the conveyor and pull the worker’s fingers or hands into the conveyor.
• Clothing or other objects like ID badge lanyards can be snagged by damaged steel wire stitching attaching the belt material’s ends.

Other conveyor-related hazards include improperly guarded sprockets and chain drives. Overhead conveyors warrant special attention because most of the conveyor’s drive train is exposed. Materials carried by overhead conveyors and broken components can fall from the conveyor system. Employees have also been injured while stepping or walking on or near conveyors [6].

Entanglement injuries frequently occur when conveyors are manually cleaned. Workers using flat blades or other tools to scrape material from belts on the return side are often drawn into in-running nip points when the tools they are using, their clothing or their hands become entangled in the moving parts of the conveyor.

Belt and chain drives used to power the head pulley are common maintenance locations with significant entanglement risks.

Abrasion

Moving flat belts can cause abrasion injuries to workers whose hands, arms, or other body parts come into prolonged contact with the belt. The belt’s surface finish and the belt material’s characteristics, combined with the motion of the belt, create the abrasion hazard. Additionally, small particles of the material carried by or embedded in the surface of the belt, including dirt and grit that may be carried onto belts used for unit loads such as cardboard boxes, can increase the abrasiveness of the belt.

Abrasion hazards are created by the moving surfaces of the head and tail pulleys and the idler rollers along the length of the conveyor. Damage to the pulleys’ surface can increase the abrasiveness of these surfaces, while some conveyor systems use knurled surfaces to increase friction between the head pulley and the belt.

Crushing

Belt tensioning devices, particularly counterweights used to maintain belt tension, automatically create crushing hazards under the counterweight and other tensioning mechanisms. Pneumatic cylinders and mechanical springs can create crushing hazards in the mechanisms and add trapped energy hazards that can cause catastrophic injuries if the belt should break during maintenance.

Other types of conveyors, like bucket conveyors, for example, bring their types of crushing hazards.

Severing

Screw conveyors commonly used for moving swarf away from the working areas on CNC lathes and used to move all kinds of particulate materials have inherent shear points where the screw passes fixed parts of the conveyor tube. These shear points create a severing hazard and significant entanglement and drawing-in hazards. Screw conveyors can easily shear parts of tools and other objects that may be put into the conveyor feed openings.

Controls

Guarding conveyor systems effectively can be challenging since access to some of the moving parts of the conveyor is required for normal use; however, head and tail pulleys and drive and tensioning systems can be effectively guarded with some thought and planning. Some general controls you might use include the following [6]:

• Install guards for all sprockets, chains, rollers, belts, and other moving parts. Guarding by location — locating moving parts away from employees to prevent accidental contact with the hazard point — is one option for guarding conveyors. It is particularly difficult, however, to use this method when guarding the in-going nip points on certain conveyors, such as roller conveyors, because the exposed rollers are crucial to the function of the conveyor.
• Use prominent warning signs or lights to alert workers to the conveyor operation when it is not feasible to install guarding devices because they interfere with the conveyor’s operation.
• Ensure that all conveyor openings, such as wall and floor openings, chutes and hoppers, have guards when the conveyor is not in use.
• Ensure that start buttons have guards to prevent accidental operation.
• Ensure that conveyor controls or power sources can accept a lockout/tagout device to allow safe maintenance practices. For crossovers, aisles, and passageways, you need to do the following:
• Ensure that all accesses and aisles that cross over, under, or adjacent to the conveyor have adequate clearance, handrails, or other guards.
• Place crossovers in areas where employees are most likely to use them.
• Ensure that all underpasses have protected ceilings.
• Post appropriate hazard warning signs at all crossovers, aisles, and passageways.
• Considering emergency egress when determining the placement of crossovers, aisles, and passageways. For emergency stops or shut-offs, you will need these engineering controls:
• Equip conveyors with interlocking devices that shut them down during an electrical or mechanical overload, such as product jams or other stoppages. When conveyors are arranged in a series, all conveyor segments should automatically stop whenever any stops.
• Equip conveyors with emergency stop controls that require manual resetting before resuming conveyor operation.
• Install marked, unobstructed emergency stop buttons or pull cords within easy reach of workers.
• Provide continuously accessible conveyor belts with emergency stop cables that extend the entire length of the conveyor belt to allow access to the cable from any point along the belt.

Guides

Learn more from these guides. You can download the original guides below.

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References

The conveyor standards listed below are invaluable references when safeguarding conveyors.

[1] Safety Standard for Conveyors and Related Equipment, ASME B20.1. American Society of Mechanical Engineers (ASME). 2018.

[2] Continuous handling equipment and systems — Safety and EMC requirements for mechanical handling of bulk materials except fixed belt conveyors, EN 618. European Committee for Standardization (CEN). 2002+A1:2010.

[3] Continuous handling equipment and systems – Safety and EMC requirements for equipment for mechanical handling of unit loads, EN 619. European Committee for Standardization (CEN). 2002+A1:2010.

[4] Continuous material handling equipment and systems — Safety and EMC requirements for fixed belt conveyors for bulk materials, EN 620. European Committee for Standardization (CEN). 2002+A1:2010.

[4] Advanced Design of Recycling Machines, Conveyor belt moving WEEE for sorting. 2019.

[5] L. Giraud, S. Massé, J. Dubé, L. Schreiber, A. Turcot, A User’s Guide to Conveyor Belt Safety, RG-490, 2nd ed. Montreal: CSST – Commission de la santé et de la sécurité du travail du Québec, 2003.

[6] Occupational Safety and Health Administration. “Safeguarding Equipment and Protecting Workers from Amputations Small Business Safety and Health Management Series”, osha.gov, 2001. [Online]. Available: https://www.osha.gov/Publications/OSHA3170/osha3170.html. [Accessed: 2021-04-16].

[7] R. Swinderman, A. Marti and D. Marshall, Foundations for Conveyor Safety, 1st ed. Stevens Point, WI: Martin Engineering Company, 2016. [Available: https://www.martin-eng.com/content/product_subcategory/667/conveyor-belt-safety] Accessed: 2019-05-01.

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Convoyeurs dans QUÉBEC. Réglement sur la santé et la sécurité du travail, c. S-2.1, r. 13, Québec, Éditeur officiel du Québec, 2012, section XXIII, art. 265-271.

CONVEYOR EQUIPMENT MANUFACTURERS ASSOCIATION, and AMERICAN NATIONAL STANDARDS INSTITUTE. Belt conveyors: unit handling conveyors, Naples, Flor., CEMA, 2002, ii, 24 p. (ANSI/CEMA 402-2003).

CONVEYOR EQUIPMENT MANUFACTURERS ASSOCIATION, et AMERICAN NATIONAL STANDARDS INSTITUTE. Belt driven live roller conveyors: unit handling conveyors, Naples, FL, CEMA, 1997, ii, 16 p. (ANSI/CEMA 403-2003).

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Material Handling Industry, Conveyor and Sortation Systems Committee. “Application Guidelines for Vertical Reciprocating Conveyors.” Available: https://www.pflow.com/wp-content/uploads/2016/10/vrc-application-guidelines.pdf. Accessed: 2019-04-27.

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