Licensed Professional Engineers
FORENSIC CLUES # 38- "Belt Conveyors" by John L. Ryan
A newsletter dedicated to keeping attorneys informed of the technical side of product liability cases.
Issue 38: Vol. 1 July/August 2010
"Belt Conveyors "
By John L. Ryan
Conveyors provide a means to transport materials continuously from one location to another. Conveyors enable production lines and complex multi-stage manufacturing processes.
Because conveyors must transport the combined weight of everything riding on the conveyor, conveyors are usually powered by high powered motors. These motors rotate a cylinder which rotates the tensioned conveyor belt. The components involved in the power transmission process have serious entanglement hazards.
During 2002-2005, there were 117 reported fatalities involving conveyor accidents, and thousands of injuries. Accidents occur most frequently when people become entangled in the in-running nip points that are found on conveyors. A nip point exists where a rotating component passes near a stationary object, or another rotating component. These hazards are very dangerous because they can pull a person into the machinery very quickly, before the person has time to react. Loose clothing can initiate a conveyor accident, if the clothing becomes caught in the nip point and begins to pull the person into the machinery.
Nip points occur where a sprocket meets a chain that transmits power from the motor to the cylinder that rotates the conveyor belt. Exposure to this nip point can result in serious injuries to a worker’s extremities.
Nip point of chain and sprocket
The motor drives the conveyor belt by rotating one of the cylinders that keeps tension in the belt. This cylinder is called the drive pulley, head pulley, or head drum. The other, undriven cylinder is referred to as a tail pulley. A nip point occurs where the rotating cylinder meets the incoming side of the conveyor belt. These nip points are very serious hazards as entanglement in these components can result in fatal injuries – a worker’s entire body can become pulled into the conveyor nip point.
Nip point of conveyor drum
Prevention of these types of accidents involve simple guarding solutions. Fixed guards can cover chain and sprockets easily. Fixed guards can also often be used on head and tail drums. Fixed guards are the most effective solution to keeping people from being exposed to the nip points on conveyors.
Fixed, interlocked guards safeguard the nip point effectively.
Some manufacturing processes may not allow safeguarding by fixed guards. In this case, access to the entire area must be restricted to prevent exposure to the hazard. Fixed guards will have to be removed for maintenance on the conveyor. Properly interlocked guards will shut power down to the conveyor when the guard is removed.
Lock-out/Tag-out is a procedure used to prevent maintenance workers from being exposed to machinery hazards, as well as to prevent accidental activation of machinery while being maintained. This involves shutting power down to machinery, and using padlocks to prevent the power from being turned on again inadvertently. OSHA has specific requirements for lock-out/tag-out procedures.
Exposed shafts are another hazard that can result in serious injury. An exposed shaft that is rotating can get clothing wrapped around it, after which the rotating shaft will continue to rotate, pulling the entangled person along with it. Exposed shafts can be minimized in the design and construction phase, and any remaining hazard can be protected with a fixed guard that prevents entanglement with the shaft.
Emergency stops are important safety features in the event of someone becoming entangled or otherwise injured in a conveyor. Stopping the conveyor quickly could save a worker’s life or minimize his injuries. For long conveyors where the control panel may be inaccessible or out of sight, an emergency stop pull cord gives workers the ability to initiate an emergency stop remotely.
OSHA standards require guarding of machine hazards. OSHA 1910.212, Machine Guarding Standard, requires employers to ensure machine hazards are safeguarded. This reads “One or more methods of machine guarding shall be provided to protect the operator and other employees in the machine area from hazards such as those created by point of operation, ingoing nip points, rotating parts, flying chips and sparks.”
OSHA 1926.555, Construction Standard for Conveyors, requires emergency stop controls at the operator’s station or at the conveyor motor, and audible warning signals before conveyor is started. This standard also calls for guarding of conveyors when they pass over work areas, and locking out and tagging power to a conveyor during repair and maintenance. Screw conveyors require guarding to prevent contact with turning flights. OSHA 1910.147 details the lock-out/tag-out requirements.
ASME B15.1, Safety Standard for Mechanical Power Transmission Apparatus, states that “All motion hazards associated with the operation of mechanical power transmission apparatus shall be eliminated by design of the equipment or protection by a guard, device, safe distance, or safe location.” Typical to other industry-produced standards, some standards produced by the conveyor industry have no mention of safety devices or safeguarding of hazardous components.
OSHA 1910.6 cites ANSI B20.1-1957, Safety Code for Conveyors, Cableways, and Related Equipment, making it a requirement for employers to meet these minimum specifications. Section 602 of this standard calls for arrangement of power transmission devices to minimize the hazard of entanglement in the device. The standard calls for nip and shear points to be guarded, and specifies that typical locations include “where belts wrap around pulleys”. New versions of ANSI B20.1, while not federally mandated, give additional requirements for conveyor safeguarding.
Conveyors make modern manufacturing possible. Nip point and entanglement hazards of conveyors can be safeguarded with minimal cost and effort. Accidents involving power transmission hazards of conveyors are preventable through proper design and safeguarding.
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