Interlocks, Light Curtains, and Presence-Sensing Devices

• Workers entering a hazard area after a safety device is bypassed or defeated
• A sensing field being blocked, misaligned, muted, or positioned incorrectly
• Machine motion continuing because stopping distance is inadequate
• Workers assuming a safeguarding device isolates hazardous energy
• Reset controls placed where the danger area cannot be observed
• Safeguarding faults ignored to maintain production

Interlocks, light curtains, laser scanners, safety mats, and other presence-sensing devices can prevent or stop hazardous machine motion when a worker opens a gate or enters a protected field.

These devices must be installed and used as part of the machine's designed safeguarding system. Their location, sensing area, response time, stopping performance, and reset method determine whether they provide effective protection.

Workers should never bypass, tape, block, misalign, jumper, or defeat an interlock or sensing device. A machine that will not run because a safety device is active may be identifying a real hazard or equipment problem.

The protected field should remain clear and should cover the intended access route. Pallets, carts, tools, product, reflective surfaces, dirt, damage, or equipment changes can interfere with detection or create an unprotected path.

A light curtain or gate interlock may stop normal machine movement, but it should not automatically be treated as complete hazardous-energy isolation. Servicing, maintenance, entry, cleaning, or jam clearing may require the site's energy-control procedure.

Reset and restart controls should be used only after the entire danger area is checked. Workers should not reset from a position where someone could remain hidden inside the protected space.

Safeguarding devices should be inspected and function-tested according to the facility's procedure. Fault messages, slow stopping, unexplained trips, intermittent operation, or damaged components should be reported.

When production changes alter the machine layout, tooling, stopping distance, access point, or product flow, qualified personnel should review whether the safeguarding system still protects the new configuration.

• Never bypass or defeat an interlock or sensing device.
• Keep sensing fields and protected access paths clear.
• Report damage, faults, misalignment, or unexplained trips.
• Verify the danger area is clear before reset and restart.
• Do not confuse a safety stop with hazardous-energy isolation.
• Function-test safeguards according to site procedures.
• Review safeguarding after process or layout changes.

• What hazard and access route does this device protect?
• Could material, equipment, dirt, or damage block the sensing field?
• Can the machine stop before a person reaches the hazard?
• Can the reset operator see the entire protected area?
• Which tasks still require hazardous-energy control?