Press Safety: Light Curtains and Two-Hand Controls

Why is press safety treated separately?

Presses are usually at the heart of the plants producing sheet metal parts in Bursa’s automotive supplier industry; in industrial zones such as Bursa OSB and Nilüfer OSB in Nilüfer, many suppliers forming sheet metal work with press lines. Press safety is therefore one of the central topics in OHS work in the region.

What press accidents have in common is that the movement is fast, the force is enormous and the danger zone, i.e. between the dies, is very close to where the hands work. Feeding parts by hand, removing a stuck part and setting the die are the riskiest moments. The result is often not a first aid case but the loss of fingers or a hand.

Annex I, item 2.8 of the Regulation on Health and Safety Requirements for the Use of Work Equipment requires that, where there is a risk of mechanical contact with moving parts that could lead to accidents, equipment be fitted with guards that prevent access to the danger zone or stop the moving parts before the zone is reached. This second phrase is the logic of light curtains and two-hand controls: stopping the ram before the hand reaches the die. For a general explanation of guard types, see our article on machine guards.

Choosing protection by type of press

The right protection depends on whether the press can interrupt its movement:

Eccentric press safety: the most common mistake

Most older eccentric presses have a key- or pin-type full-revolution clutch. When the pedal is pressed, the clutch engages and the ram does not stop until it has completed its cycle. When a light curtain is fitted to such a press, it cannot stop the ram even if it detects the hand; worse, it gives the operator the false impression of being protected. The same problem applies to two-hand controls: even if a hand is pulled away from the button, the ram keeps coming down.

Realistic options for eccentric press safety are:

• Closed die: The die opening is designed to be too narrow for a finger to enter, and feeding is done from outside the die.
• Fixed guard: The die area is enclosed, leaving only the opening the part will pass through.
• Interlocked guard with guard locking: The guard cannot be opened until the ram reaches a safe position.
• Conversion: The press is converted to a monitored brake and clutch system. This is an extensive modification and requires the machine to be reassessed.
• Feeding aids from outside the die: Tongs, vacuum grippers or slide feeds reduce the need for the hand to enter the die; but on their own they do not count as protection and are used together with a guard.

An improvement plan for old presses without CE marking is a separate topic; see our article on bringing old machines without CE marking into compliance. When buying a new press, our article on the Machinery Safety Regulation and CE also guides you on the documents to check.

Light curtain distance calculation

When the light curtain detects a hand, it gives a stop command; but the ram keeps moving for a while. So the curtain must be mounted far enough away that the ram stops before the hand reaches the die. The basic formula in the 2024 edition of the safety distance standard EN ISO 13855 is:

S = (K × T) + DDS + Z

• S: Minimum distance from the curtain to the danger zone (mm); it cannot be less than 100 mm.
• K: Approach speed of the body; 2,000 mm/s for upper limbs, 1,600 mm/s for walking.
• T: Overall stopping time of the system (s): the curtain’s response time, the safety control circuit and the press’s own stopping time.
• DDS: Additional reach distance depending on the protective device; for a light curtain it depends on the curtain’s resolution.
• Z: Application-dependent additional allowance, such as measurement uncertainty and brake wear.

Determine the DDS and Z values according to the edition of the standard used in the documentation of your curtain and press. The main lesson of the formula is simple, though: in the light curtain distance calculation, the decisive variable is the stopping time.

Example: On a hydraulic press, suppose the total stopping time of the curtain, control circuit and press has been measured at 0.15 seconds. The K × T term alone is 2,000 × 0.15 = 300 mm; DDS and Z are added on top. If the stopping time increases to 0.25 seconds through valve or brake wear, the same term becomes 2,000 × 0.25 = 500 mm. The required distance has increased by 200 mm; since the curtain has not moved, this difference becomes a gap through which the hand can reach the die before the ram stops. This is why the stopping time should be measured periodically with a stopping time measuring device and the result recorded.

Points to watch during installation:

• Make sure the die cannot be reached under, over or around the side of the curtain; gaps are closed with fixed guards.
• If there is space for the operator to stand between the curtain and the die, the press must not restart without the curtain being reset.
• Muting and blanking functions, which disable certain beams of the curtain, are used only on the basis of a risk assessment and with the distance recalculated.

Two-hand control requirements

A two-hand control keeps the hands away from the danger zone by requiring the operator to keep both hands on the buttons. The basic requirements for it to provide protection (EN ISO 13851):

1. The press does not operate unless the two buttons are pressed simultaneously; the standard defines a limit of 0.5 seconds for this simultaneity.
2. When one of the buttons is released, the hazardous movement stops.
3. For a new cycle, both buttons must be released and pressed again.
4. The buttons are positioned and shielded so that they cannot be pressed at the same time with one hand, with a hand and an elbow, or with an object.
5. The control station is mounted at a safety distance at which the ram stops before a hand leaving the button reaches the die; this distance is also calculated from the stopping time using the same logic.

Know the limits of two-hand controls too:

• They protect only the person using them. A second person working behind or beside the press is not protected; when several people work together, a separate control for each operator and a requirement to press together are needed.
• They are open to bridging. Holding one of the buttons down permanently with tape, a wedge or an extra cable arrangement is a known cause of press accidents. A layout that makes bridging difficult and a function test at the start of each shift are therefore important.

Safe working during die changes

Die changing and setting are different from normal production: guards are open and people are between the dies. So the work should be carried out under a written instruction:

1. Isolate and lock out the energy: Electrical, hydraulic and pneumatic energy is locked and tagged; zero energy is verified by testing.
2. Secure the ram mechanically: A die safety block is placed between the ram and the bed; hydraulic pressure or the brake alone is not considered a safeguard.
3. Set in low-speed mode: Die closing adjustment is done in a key-selected setting (inching) mode and at low speed.
4. Move the die correctly: The die is moved with a crane or die cart of suitable capacity that has been periodically inspected; slings and hooks are checked before use.
5. Test before putting into service: Guards are fitted, the light curtain is tested with the test rod and the two-hand control with a function test, and the first stroke is made under control.

Preparing the die change instruction and monitoring its application on site is part of our OHS specialist service. To score the risks on a press line, see the press example in our article on the Fine-Kinney method.

Periodic inspection and start-of-shift checks

Under Annex III of the Work Equipment Regulation, presses are subject to periodic inspection once a year unless a shorter period is specified in the relevant standard; the criteria of TS EN ISO 16092-1 for mechanical presses and TS EN ISO 16092-3 for hydraulic presses are used. The inspection is carried out by authorised persons registered on EKİPNET (the Ministry’s register of authorised inspectors). For the inspection schedule, see our periodic inspection page and our article on periodic inspection intervals for work equipment.

The annual inspection does not replace the short check at the start of each shift:

Forming of metals by pressing is in the Annex 1 list of the vocational training regulation; a press operator must hold a vocational training certificate appropriate to the job. For the list, see our article on occupations requiring vocational training. Our approach to press-intensive businesses in the region is set out on our automotive supplier industry and Nilüfer OSGB pages.

Frequently Asked Questions

Is fitting a light curtain to an old eccentric press enough?

Not if the press has a full-revolution clutch. On these presses, the ram completes its cycle once the clutch engages; even if the curtain detects the hand, it cannot stop the movement. A closed die, a fixed or interlocked guard, or conversion to a monitored brake and clutch is needed.

Which value matters most in the light curtain distance calculation?

The overall stopping time. Taking the approach speed for upper limbs as 2,000 mm/s, every 0.1-second increase in stopping time increases the required distance by 200 mm. This is why the stopping time should be measured and recorded periodically.

Can a second person work at the press when there is a two-hand control?

A two-hand control protects only the operator using it. If a second person is to work at the press, they must also be given a separate control, and the press must operate only when all controls are pressed together; otherwise the second person is unprotected.

How often is a press periodically inspected?

Under Annex III of the Work Equipment Regulation, mechanical and hydraulic presses are inspected once a year unless the standard specifies a shorter period. The inspection is carried out by authorised persons registered on EKİPNET; start-of-shift function tests are the operator’s job.