ASP Exam – Control of Hazardous Energy
Machinery and equipment in the workplace create many complex hazards which the safety professional must be prepared to protect workers from. Workers may become caught in a machine or tool, may be struck by a tool, moving piece of equipment, or the material being worked on, and may experience cumulative trauma injuries as a result of using tools. Many pieces of equipment include power sources which may be hazardous to an employee, including electrical power, combustible fuels, hydraulics and pneumatics which operate at high pressures, etc. Machines move in five distinct ways:
Rotation, such as a spindle, chuck, flywheel, or drill bit. Rotating equipment tends to grab clothing or hair, which can quickly pull a worker towards or into a machine.
Reciprocating or Transverse Motion, a back and forth motion, is dangerous when a worker enters the line of fire, resulting in being struck by the equipment or material being worked on. It is also possible to become pinched or sheared between moving and immobile parts of the machinery or adjacent structures or equipment.
Cutting Actions, such as those produced by saws, mills, planing machines, lathes, and grinders are designed to remove material from a piece of stock. They can also remove portions of a worker or bystander that gets in the way of those activities.
Punching, Shearing, and Bending motions are often produced by two or more machine components that come together, with one sometimes being stationary. The point of operation and surrounding areas create a hazard to any human or unintended materials that enter it.
In-Running Nip Points are created by components of equipment that run toward or each other or run toward a fixed point on the equipment. Belts, chains, gears, and pulleys all create in-running nip points.
Types of Machine Safeguards
Guards are the most widely preferred method for machine safeguards. Guards must be a permanent part of a machine or piece of equipment, they must prevent access to any dangerous parts of a machines operation, and they must be constructed in a manner which prevents them from breaking or becoming worn even under heavy use. Any area where a machine action occurs that closes to 3/8” or less should be considered for guarding, as 3/8” is the approximate thickness of a finger. Guards may have opening in them to insert materials into a machine, allow access for inspection or servicing, and to monitor the action of a machine. Guards around power transmission devices should totally enclose the components.
Devices are controls that inhibit normal operation of a machine if a person is within or near a hazardous area of a machine or piece of equipment. Additionally, devices may refer to interlocks that render the device inoperable is access panels around any hazardous area are opened. Emergency shut-off controls may also be within reach of hazardous areas.
Distance places the point of operation or other hazards of a machine out of reach to prevent accidental contact. The minimum distance required from the floor or walking surface to power transmission components is typically 7 to 8 feet if distance will be used to protect workers.
Location means placing the machine where people are excluded or only accessed for servicing.
Point of Operation Guards
Point of operation guards protect users from the location that the machine does its work, whether that be punching, pressing, forming, bending, etc. Several types of guards exist, but all are meant to exclude workers from a hazardous area or render a machine inoperable if that area is entered. The types of guards most commonly used are:
- Enclosure guards, which are fixed to the machine in a manner that cannot be removed without tools and completely excludes humans from the point of operation. The guard should not create additional hazards such as pinch points.
- Interlocked guards, which use an electrical interlock device to break a circuit when a door or access panel is opened.
- Adjustable guards, which can be adjusted for different operations.
- Ring guards, which allows materials to pass underneath it but protects the remaining area around a cutter.
- Hood guards, which float vertically and allow materials to pass underneath, but protect the top of a blade, such as on a table saw.
- Grinding wheel guards, which help contain portions of a wheel that shatters and keep operators from coming in contact with a wheel.
Point of Operation Devices
When it is not feasible to supply a point of operation guard, devices may be used to protect workers from the point of operation. Devices which can do so include:
- Automatic or semi-automatic feed and ejection of materials
- Gates or movable barrier devices
- Presence-sensing devices, including mats, photoelectric sensors, radio frequency fields, and mechanical sensing devices
- Pull-out devices
- Restraint devices
- Sweep devices
- Two-hand controls
- Hand-feed tools
- Awareness barriers and signals
- Emergency stop controls
Additional Machine Safeguards
Additional machine safeguards may be present to provide worker protection and can include:
- Anti-repeat devices that only allow a machine to cycle one time
- Brakes that keep elevated portions of machinery in place until a machine is cycled
- Foot controls with guarding over the control to prevent materials from inadvertently falling and cycling the machine
- Jog controls that move the machine slowly for servicing
- Mode selection, including mode selection that is controlled by a key
- Run controls that have guarding to prevent inadvertent cycling of a machine
- Blocks or stops to prevent machine components from falling
- Anti-kickback devices
- Inch Controls or Low-Energy Operation that allow an operator to reduce hazards by moving a machine slowly during set up or maintenance
In addition to the engineering controls described above, it is important to ensure that each machine operator is trained and understands the functions and controls of equipment they will be operating, the hazards the equipment can create, and what controls are presently on the machine and how to ensure that controls and guards are functioning properly. Equipment should be properly inspected and maintained, and operators should be dressed appropriately, use all prescribed PPE, and ensure they do not have any loose clothing, jewelry, or long hair if the machine operates in a manner where loose objects would be unsafe around them.
Lockout / Tagout
Lockout / tagout (or energy control) procedures safeguard workers from the unexpected release of hazardous energy while they are performing maintenance and servicing machines. When locking out a machine, all sources of energy must be properly considered and accounted for, including electrical, pneumatic, hydraulic, and mechanical sources. Workers who will be performing lockout / tagout must receive training to become authorized in the proper use of LOTO procedures. All employees working in an area where energy control procedures are used need to be instructed in the purpose of the procedures and the prohibitions against attempting to restart equipment that is currently locked or tagged out.