Requirements for Safeguards
Machine safeguards must meet these minimum general requirements:
- Prevent contact: The safeguard must prevent hands, arms or any other part of a worker’s body from contacting dangerous moving parts.
- Be secure: Workers should not be able to easily remove or tamper with the safeguard. Guards and safety devices should be made of durable materials that will withstand normal use. They must be firmly secured to the machine where possible or secured elsewhere if attachment to the machine is not possible.
- Protect from falling objects: The safeguard should ensure that no objects can fall into moving parts.
- Create no new hazards: A safeguard defeats its own purpose if it creates a hazard such as a shear point, a jagged edge or an unfinished surface. Edges of safeguards should be rolled or bolted so that they eliminate sharp edges.
- Create no interference: Any safeguard that impedes a worker from performing a job quickly and comfortably might be bypassed or disregarded. Proper safeguarding can enhance efficiency because it relieves a worker’s injury apprehensions.
- Allow safe lubrication: If possible, the machine should be able to be lubricated without removing the safeguard. Locating oil reservoirs outside the guard, with a line leading to the lubrication point, will reduce the need for the operator or maintenance worker to enter the hazardous area.
Types of Safeguarding
The type of operation, the size or shape of stock, the method of handling, the physical layout of the work area, the type of material and production requirements or limitations help determine the best method for safeguarding.
Safeguards are classified as either guards or devices
Guards are barriers which prevent access to dangerous areas. There are four general types of guards:
- Fixed guards are permanent parts of a machine. These guards are preferable because they’re simple and permanent.
- Interlocked guards automatically shut off or disengage power through a tripping mechanism when it is opened or removed. The machine cannot cycle or start until the guard is replaced.
- Adjustable guards are useful because they accommodate various sizes of stock.
- Self-adjusting guards allow the opening of these barriers to be determined by the movement of the stock. As the operator moves the stock into the danger area, the guard is pushed away, providing an opening that only is large enough for the stock.
Safety devices perform several functions. They may stop a machine if any part of a body is inadvertently placed in the danger area. They may restrain or withdraw an operator’s hands from the danger area. They may require both hands on a control, therefore keeping both hands out of the danger area. They may also provide a synchronized barrier with the machines operating cycle to prevent entry into the danger area.
- Presence-sensing devices are divided into two groups. Photoelectrical devices use light sources and controls that can interrupt the machine’s operating cycle. Radiofrequency or capacitance devices use a radio beam that is part of the machine control circuit. When the capacitance field is broken, the machine will stop or not activate.
- Electromechanical sensing devices have a probe or contact bar that descends to a predetermined distance when the operator initiates the machine cycle. If there is an obstruction preventing it from descending to its full, predetermined distance, the control circuit does not start the machine cycle.
- Pullback devices use cables attached to the operator’s hands, wrists and/or arms. They are used primarily on machines with stroking-action hazards. When the slide/ram is up (between cycles), the operator has access to the points of operation. When the slide/ram begins to descend, a mechanical link automatically assures that the operator’s hands move away from the point of operation.
- Restraint (hold-back) devices allow the operator’s hands to travel only in a predetermined safe area and prevent the operator from reaching into a danger area. Cables or straps are attached to the operator’s hands and a fixed point. No extending or retracting actions are involved.
- Safety trip controls, such as pressure-sensitive body bars, safety tripods and safety tripwire cables, quickly deactivate a machine in an emergency.
- Two-hand controls require both hands and constant pressure on the controls for the machine to operate.
- Two-hand trip requires in sync application of both the operator’s control buttons to activate the machine cycle after which the hands are free. To be effective, both the controls and trips must be located so that the operator cannot use two hands or one hand and another part of their body to trip the machine.
- Gates are movable barriers that protect the operator at the point of operation before the machine cycle starts. To be effective, gates must be interlocked so that the machine will not begin a cycle unless the gate guard is in place.
Though not actual guards or devices, location and distance can keep employees safe by placing a machine in an infrequently traveled area or where it’s dangerous moving parts are not accessible. A thorough hazard analysis of each machine and situation is essential before using this safeguarding technique
Guards designed and installed by the machine producer are desirable because they conform to the design and function of the machine, and they can be designed to strengthen the machine or to serve some additional functional purpose.
User-built guards are sometimes necessary and have some advantages. Often, with older machines, they are the only practical solution. They also might be the only choice for mechanical power transmission apparatuses in older plants, where machinery may not be powered by individual motor dries. User-built guards can be designed and built to fit unique and changing situations and can be installed on individual dies and feeding mechanisms. They also permit options for point-of-operation safeguards. When workers design and install machine guards, they develop a better knowledge of those guards and how they work.
However, there are some disadvantages. User-built guards might not conform well to the configuration and function of the machine and might be poorly designed or built.
Metal, plastic, wood or any other material that is substantial enough to withstand impact and prolonged use are all used as construction materials for machine guards. In many circumstances, metal is the best material for guards. It might also be feasible to use plastic where higher machine visibility is required. Guards made of wood are generally not recommended because of their flammability and lack of durability and strength.
29 CFR 1910.219 Mechanical power-transmission apparatus, states that wood guards can be options in woodworking and chemicals industries, and in industries where vapors or gases or other conditions could deteriorate metal guards. Wood guards also may be used in construction work and in outdoor locations where extreme cold make metal guards undesirable. In all other industries, wood guards are not allowed, per 29 CFR 1910.219 (o)(2).
The list of possible machinery-related injuries created by moving machine parts is long - amputations, lacerations, crushing injuries, and abrasions, Machine safeguards are essential for protecting worker from these preventable injuries. Please click the link to review Grainger’s product line of machine guards.
29 CFR 1910 Subpart O
OSHA Machine Guarding E-Tool