Machines, automation and robots

Machines are the heart of most plants, and they cause many of the worst injuries: amputations, crushing, entanglement and being struck by ejected parts. HSE-215 covers machine guarding in depth, HSE-210 covers lockout, and ROB-440 covers industrial robot cells. This lesson takes the plant-wide view: how machinery hazards show up in daily work, how a plant decides which safeguards to use, how automation changes the picture, and what everyone on the floor needs to know.

Where machines hurt people

Machine hazards concentrate at a few places. The point of operation is where the machine does its work on the material: cutting, pressing, punching, bending, shearing, forming. Power transmission parts carry energy to the point of operation: shafts, couplings, belts, pulleys, chains, sprockets and gears. Other moving parts include feed mechanisms, conveyors, rotating drums and reciprocating arms. Nip points form wherever two parts move together, or one part moves past a fixed object. Each can grab clothing, hair or a hand and pull it in faster than anyone can react.

In the United States, amputations are among the most serious machine injuries, and OSHA has run a national emphasis program on amputations in manufacturing for many years. Machine guarding (1910.212) was the tenth most cited OSHA standard in fiscal year 2025, and lockout/tagout (1910.147) the fourth. Specific standards cover mechanical power presses (1910.217), woodworking machinery (1910.213) and mechanical power-transmission apparatus (1910.219), and the ANSI B11 series gives detailed guidance.

Choosing safeguards

Safeguarding follows the hierarchy of controls. The best option is to design the hazard out, for example by enclosing the point of operation or using automatic feeding so nobody needs to reach in. Next come fixed guards, which are simple and reliable. Where people need regular access, interlocked guards or presence-sensing devices such as light curtains and safety mats stop the machine when someone enters. Two-hand controls keep both hands away during the hazardous motion but protect only the operator. Training, signs and PPE support these but cannot replace them.

Safety distance for presence-sensing devices

A light curtain stops a machine when a hand or body breaks the beams, but the machine takes time to stop. If the curtain is too close, a hand can reach the hazard before motion ends. Standards set a minimum safety distance based on the approach speed of a hand or body and the total stopping time. The simplified form used in CSA Z432, ISO 13855 and ANSI B11.19 multiplies an approach speed by the stopping time and adds an allowance that depends on how far a hand can penetrate the curtain before it is detected.

# Minimum safety distance for a vertical light curtain (simplified, illustrative).
# K = hand approach speed, T = total stopping time, C = penetration allowance.
K = 2000          # mm/s for close approach (a larger K applies at longer distances)
for T_ms in (80, 150, 250):
    T = T_ms / 1000
    for res_mm in (14, 30):                     # detection capability of the curtain
        C = max(0, 8 * (res_mm - 14))           # allowance in mm
        S = K * T + C
        print(f"stop time {T_ms:>3} ms, resolution {res_mm} mm -> S = {S:5.0f} mm ({S / 25.4:4.1f} in)")

stop time  80 ms, resolution 14 mm -> S =   160 mm ( 6.3 in)
stop time  80 ms, resolution 30 mm -> S =   288 mm (11.3 in)
stop time 150 ms, resolution 14 mm -> S =   300 mm (11.8 in)
stop time 150 ms, resolution 30 mm -> S =   428 mm (16.9 in)
stop time 250 ms, resolution 14 mm -> S =   500 mm (19.7 in)
stop time 250 ms, resolution 30 mm -> S =   628 mm (24.7 in)

The calculation shows why stopping time matters. A press that takes 250 ms to stop needs the curtain more than half a meter away. If the brake wears and stopping time grows, the same curtain is no longer safe, which is why stopping performance must be checked regularly with a stop-time measuring device.

Lockout and its alternatives

Guards protect people during normal production. When people need to service, maintain, clean or clear jams on a machine, they often have to get past the guards, and then hazardous energy must be controlled. HSE-210 covers lockout in detail. In brief: identify every energy source, shut the machine down, isolate each source, apply personal locks and tags, release stored energy, and verify zero energy by trying to start the machine before anyone reaches in.

OSHA's lockout standard has a narrow exception for minor servicing done during normal production operations: tasks that are routine, repetitive and integral to the use of the equipment may be done under alternative measures that provide effective protection, such as interlocked guards or trapped-key systems. ANSI/ASSP Z244.1 describes how to justify alternative methods by risk assessment. Anything beyond minor servicing requires full lockout.

Automation and robots

Automation removes people from many hazardous tasks: robots do welding, palletizing and painting, and automated guided vehicles move material. It also creates new hazards. Robots move quickly and can change direction unexpectedly, they can store energy, and they may restart automatically when a sensor clears. Most robot injuries happen not during normal operation but during programming, teaching, troubleshooting and maintenance, when people are inside the cell. Collaborative robots designed to work beside people use force and speed limits, but they still need a risk assessment of the whole application, including the tool and the part.

ANSI/RIA R15.06, based on ISO 10218, sets requirements for industrial robots and robot systems in the United States, including perimeter safeguarding, reduced speed for teaching, enabling devices and safe restart. ROB-430 and ROB-440 cover these in depth.

Machinery safety for everyone on the floor

Whatever your role, a few machine safety rules apply in every plant. Never reach into a machine you have not isolated, even for a second. Never bypass or defeat a guard or interlock. Report guards that are damaged, missing or hard to use, because a guard that interferes with work will eventually be removed. Keep loose clothing, jewelry, long hair and gloves away from rotating parts; gloves in particular can be caught by drills, lathes and rollers. Know where every emergency stop is, but remember that an emergency stop is not a lockout device.

Conveyors: the everyday killer

Conveyors deserve special mention because they are everywhere in plants and are involved in a large share of serious machinery injuries. The danger points are the in-running nips where a belt meets a pulley, especially the tail and head pulleys, take-ups, and transfer points between conveyors. Material builds up at these points, and workers reach in to clean or clear it while the belt is running. Clothing, gloves or a hand can be drawn in within a fraction of a second, and the force is enough to cause amputation or death. Pull-cord emergency stops along a conveyor help in an emergency but do not prevent the injury.

Effective controls include nip guards and enclosures at every pulley, guards designed so that cleaning can be done from outside or with the conveyor locked out, belt scrapers and skirting to reduce spillage, and spillage-clearing procedures that require lockout. Many plants have found that conveyor injuries fall sharply when guards are designed with maintenance and cleaning in mind, because people stop needing to remove them.

Buying and modifying machines safely

Most machinery hazards are cheapest to fix before the machine arrives. Purchase specifications should require compliance with OSHA standards and the relevant ANSI B11 standard, a documented risk assessment from the supplier, and guarding that allows cleaning and maintenance without removal. Used and imported machines often need upgrading, and any modification that affects guarding should be reviewed by a qualified person before the machine is used again.