Protecting against the hazards created by mechanical motion is not only a priority for manufacturers; it’s also required by law. OSHA regulations state that at least one method of machine guarding must be supplied to protect workers in the machine area from hazards at the point of operation. Employers must also provide guards to protect operators and other employees from rotating parts, ingoing nip points, and flying debris.
Machine safeguards are typically grouped as either devices or guards, and each category has a variety of types. This guide will help you answer the question, what are the types of machine guards.
Guards vs. Devices
While all measures described here refer to machine safeguards, they are divided between guards and devices. A guard provides a physical barrier that will prevent contact with the dangerous part of the machine. Physical guards are often fixed to the machine, but they can also be interlocking, adjustable, or self-adjustable.
Safeguarding devices are used to limit or prevent access to the dangerous area using a variety of technologies. Some examples of devices include those that sense the presence of a hand, arm, or body part and stop the machine’s operation, trip controls, or devices requiring two hands to be on the controls to perform functions.
Different Types of Guards
Guards that create a physical barrier between the worker and the danger zone must be made to withstand the vibrations of the machine, impact from workers or parts, and be properly fitted to the machine. In most cases, guards should require special tools to be removed. Physical guards are categorized into these general types:
Fixed, Adjustable, & Self-Adjusting Guards
A fixed guard is a simple device attached to the machine designed to cover hazardous mechanical motions and prevent entry from hands or fingers. A well-designed fixed guard will also prevent the operator from reaching over or under the guard into the point of operation.
Some fixed guards are adjustable to provide a limited access opening that allows workers to insert or remove material. For example, a guard on a band saw or milling cutter can be raised or lowered depending on the thickness of the material. Another example is a crown guard, which adjusts automatically as the material or tool moves, such as those found on circular saws and some types of drills.
An interlock guard is designed to prevent workers from making a hazardous maneuver or adjusts the machine to a safe state if a dangerous maneuver is performed. A common way for these guards to work is to prevent a machine from operating unless the guard is in position or prevent a guard from being removed until moving parts have come to a stop.
While interlock guards usually involve some type of physical barrier system, modern interlock guards often rely on a combination of technologies to be safer and more effective. For example, sensors, actuators, and lasers are frequently used to detect when an object enters an area at an inappropriate time and either prevents a machine from being started or shuts down an operating machine.
Machine Safeguarding Devices
Safeguarding devices are designed to perform different functions to keep workers safe. They can be used independently, as part of the operating cycle, or in conjunction with barrier guards. Here are several examples of devices and how they work.
- Sensing Devices. This type is used to determine when a person or object is in a hazardous area. Sensors can use light, radiofrequency, or a physical probe to observe the area. If the sensors detect an object, they can stop the machine from running or prevent it from being started.
- Pullback & Restraint Devices. These are typically designed to keep an operator’s fingers, hands, or arms away from the point of operation. A pullback device will bring hands to safety before the machine starts, and a restraint prevents them from extending into moving machine parts completely.
- Safety Trip Controls. A safety trip can use a variety of sensors, including pressure-sensitive body bars, tripwires, or safety tripods. Their function is to immediately deactivate a machine in an emergency.
- Two-Hand Devices. The purpose of these devices is to keep the operator’s hands in a fixed position while the machine is operating. Two-hand controls require the operator to exert constant pressure on the controls at all times. A two-hand trip requires the operator to press a button with each hand to start the machine, and then the operator’s hands are free.
Choosing the Right Guard
The safest guards are those designed by the manufacturer of the machine, as they have been built to conform to the machine’s function to avoid preventable injuries. These guards can also be engineered to strengthen the machine or to provide additional functions. In some cases, the unique conditions of a work area or a simple lack of suitable guards from a machine can require a custom safeguarding solution.
While some companies may choose to build these solutions in-house, this can lead to dangerous shortcomings and fail to protect workers from all potential hazards. To ensure the highest levels of safety are achieved in every workplace, custom machine guards should always be engineered and installed by a machine safety consultant.