The Definition of Two-Hand Control

Definition of Two-Hand Control

Two-hand control is a safeguarding device that requires the operator to use both hands on two separate controls at the same time to start a machine cycle and, for true two-hand control, to hold them during the hazardous part of the motion.

The idea is simple. If both hands are on the buttons, neither hand can be in the point of operation. That makes two-hand control a common safeguard on mechanical power presses, press brakes, riveting and staking machines, small assembly presses and some packaging equipment.

It matters because hand injuries on presses are often amputations. But two-hand control only works when it is designed, mounted and maintained correctly, and it only protects the person at the controls. Machine operators, setup technicians, maintenance staff and safety managers all need to understand its limits.

How Two-Hand Control Works

Two-Hand Control vs. Two-Hand Trip

• Two-hand control: the operator must keep both hands on the controls during the hazardous portion of the stroke. Releasing either button stops the motion. It is used on part revolution clutch presses that can stop mid-stroke.
• Two-hand trip: an actuating means that requires both hands at the same time to trip a full revolution clutch. Once tripped, the press completes its cycle and the operator can let go. Protection comes from distance, so the hands cannot reach the die before the slide closes.

Key Design Features

• Concurrent actuation: both controls must be operated at the same time. Pressing one and then the other should not start the cycle.
• Anti-repeat: a new cycle requires the operator to release both buttons and press them again. Holding the buttons down should not produce a second stroke.
• Protection against unintentional operation: each button sits in a ring guard or recess so it cannot be bumped or pressed by a forearm.
• Separation: buttons are spaced and mounted so one hand plus an elbow, knee or other body part cannot operate both.
• One set per operator: when more than one person works the machine, each operator gets their own controls, and all must be actuated to run the cycle.

Limitations

• Protects only the operator: helpers, material handlers and passersby are not protected, so guards or a light curtain may still be needed.
• Vulnerable to tie-down: taping down one button or bridging both with a board defeats the device. This is a common form of bypassing safety devices.
• Depends on mounting distance: controls placed too close let a fast hand reach the die before motion stops.

Regulations and Standards

OSHA 29 CFR 1910.217

29 CFR 1910.217 defines both two-hand control and two-hand trip for mechanical power presses. Each hand control must be protected against unintentional operation and arranged by design, construction and/or separation so that concurrent use of both hands is required. Anti-repeat is required, and where multiple operators are used, each operator must have their own set of controls.

The rule sets safety distances. For two-hand control on part revolution presses, Ds = 63 inches per second multiplied by Ts, the stopping time of the press. For two-hand trip on full revolution presses, Dm = 63 inches per second multiplied by Tm, the maximum time it takes the press to reach bottom dead center after it is tripped. Presses using two-hand control also need a brake monitor and control reliability. See mechanical power press safety for the wider requirements.

ISO 13851

ISO 13851 classifies two-hand control devices into types I, II, IIIA, IIIB and IIIC. All types require concurrent actuation of both controls. Type II and higher also require both controls to be released before a new cycle. Type III devices add synchronous actuation, meaning both controls must be pressed within 0.5 seconds of each other. The A, B and C variants of Type III differ in the reliability of the control system behind them.

ANSI B11.19

ANSI B11.19 covers the design, construction, installation and use of safeguarding devices, including two-hand control and two-hand trip. It includes safety distance calculations that account for machine stopping time and control response times. Check the current edition for exact formulas.

Good Practices for Two-Hand Control

• Calculate safety distance: measure actual stopping time and mount the controls at or beyond the required distance from the hazard.
• Use ring guards: recess or shroud each button so it cannot be pressed by accident or with a forearm.
• Space the buttons: mount them far enough apart that one hand and an elbow cannot operate both.
• Fix the mounting: bolt control stations in place. Portable stations should only be movable by authorized people and must still meet the safety distance.
• Guard the rest of the machine: add barriers or presence-sensing devices for helpers and anyone else near the hazard zone.
• Test every shift: confirm concurrent actuation, anti-repeat and release-to-stop work before production starts.
• Treat tie-downs as serious: investigate every bypass and fix the reason behind it, such as awkward button placement.

Example of Two-Hand Control

A small appliance parts manufacturer ran a part revolution press with a two-hand control station. A helper stood beside the press to remove finished parts. One afternoon, the helper reached toward the die to clear a jammed part just as the operator pressed both buttons. The helper pulled back in time, and the near miss was reported.

The investigation found the two-hand control protected only the operator. The company added a fixed guard on the helper's side of the die and a light curtain at the rear opening. It also moved the control station back after a stop-time test showed it sat too close. Two-hand control stayed in place for the operator, now as one layer among several.

Frequently Asked Questions: Two-Hand Control

What is the difference between two-hand control and two-hand trip?

Two-hand control requires the operator to hold both buttons during the hazardous part of the stroke, and releasing them stops the motion. Two-hand trip only starts a full revolution cycle, after which the operator can let go. Two-hand trip relies entirely on mounting distance for protection.

What is anti-repeat on a two-hand control?

Anti-repeat means the machine will complete only one cycle per actuation. The operator must release both controls and press them again to start the next cycle. This prevents an unexpected second stroke.

How far apart should two-hand control buttons be?

The buttons must be far enough apart, and guarded, so that one hand plus an elbow or other body part cannot operate both. Separately, the station must sit at a distance from the hazard based on the machine's stopping time.

Does two-hand control protect other workers?

No. It only keeps the operator's hands on the controls. Helpers, material handlers and anyone else near the machine need other protection, such as guards or presence-sensing devices.