The Definition of Mechanical Hazard

Definition of Mechanical Hazard

A mechanical hazard is any condition in which the movement of machinery, tools, equipment or materials could injure a person. Mechanical hazards can cut, crush, shear, puncture, entangle, draw in, strike or throw objects at a worker. They are found anywhere machines are used, from manufacturing, food processing and agriculture to construction, warehousing and maintenance work.

Mechanical hazards cause many of the most serious workplace injuries, including amputations, fractures, crush injuries and deaths. They often involve stored or moving energy, so they are closely linked to caught-in or caught-between and struck-by hazards.

Standards such as ISO 12100 for machinery safety and OSHA's machine guarding rules in 29 CFR 1910 Subpart O are designed to control mechanical hazards through design, guarding and safe work practices.

Types of Mechanical Hazards

Hazardous motions

• Rotating: shafts, couplings, spindles, flywheels and rollers that can catch hair, clothing or gloves.
• Reciprocating: back-and-forth or up-and-down motion, such as press rams and saw blades.
• Transverse: straight-line movement, such as conveyor belts and moving tables.

Hazardous actions

• Cutting and shearing: blades, knives, shears and saws.
• Punching and stamping: presses that drive tools into material.
• Bending and forming: press brakes and rolling machines.

Hazard points

• In-running nip points: where two parts rotate toward each other or a belt meets a pulley, drawing in anything that touches them.
• Pinch and crush points: where moving parts close together or against a fixed part. See danger zone.
• Ejection: flying chips, broken tools or workpieces thrown from machines. See kickback.
• Stored energy: springs, hydraulics, pneumatics and gravity that can move parts unexpectedly. See kinetic energy.

Controlling Mechanical Hazards

• Design: remove pinch points, enclose moving parts and reduce speeds or forces at the design stage.
• Guarding: use fixed, interlocked and adjustable guards and presence-sensing devices. See machine guarding.
• Energy isolation: use lockout/tagout before maintenance, cleaning or clearing jams.
• Safe work practices: no loose clothing, jewelry or long hair near moving parts, and use tools rather than hands to feed or clear material.
• Training and supervision: make sure operators know where hazards are and how controls work.
• Inspection: check guards and devices regularly and report damage immediately.

Example of Mechanical Hazard

At a sawmill, a worker reached toward a conveyor's tail pulley to remove a wood offcut while the conveyor was running. His glove was caught in the in-running nip point between the belt and pulley, and his hand was pulled in, causing serious injuries.

The investigation found that the tail pulley guard had been removed months earlier during a repair and never replaced. The mill installed a new fixed guard, added guard checks to daily pre-start inspections and retrained workers that clearing debris near moving parts requires the conveyor to be stopped and locked out.

Frequently Asked Questions: Mechanical Hazard

What are examples of mechanical hazards?

Examples include rotating shafts, conveyor nip points, saw blades, press rams, gears, chains and sprockets, and parts that can be thrown from machines.

What is the difference between a mechanical hazard and an electrical hazard?

A mechanical hazard involves physical movement that can strike, cut or crush. An electrical hazard involves contact with electric current or arc flash.

What is an in-running nip point?

It is a point where two parts move together, such as a belt and pulley or two rollers, and can pull in fingers, hands or clothing.