ANSI B11.19 light curtain distance for safer machinery

ANSI B11.19 sets performance criteria for safeguarding, including the minimum distance between a light curtain and hazardous machine motion. It gives risk assessors a repeatable way to ensure an operator cannot reach the danger zone before the machine stops.

The core relationship is S = K × T + C, where S is safety distance, T is total stopping time, K is assumed approach speed and C covers bodily intrusion. The result must be checked against the installed system rather than copied from a generic worksheet.

For Australian workplaces, this matters wherever automated or imported equipment is used. A Melbourne component workshop, a Sydney food-processing line, a Brisbane construction plant and a Perth mining maintenance bay may mix different guarding and control gear while needing the same defensible calculation.

Scope and risk assessment

ANSI B11.19 addresses safeguarding performance rather than prescribing one type of guard. Light curtains, fixed guards, interlocks, presence sensing and control measures can form part of a risk control strategy.

For an Australian site, document the task, exposed hazards, access routes, possible body-part intrusion and foreseeable misuse. Check the result against the WHS Regulations, applicable state or territory requirements, Safe Work Australia model codes and relevant Australian Standards such as AS/NZS 4024. ANSI B11.19 is not automatically Australian law, but it is a useful engineering benchmark.

Minimum distance calculation

The calculation is S = K × T + C. Use SI units: K is normally 2000 mm/s for the assumed human approach speed, T is measured in seconds, C is in millimetres and S is the resulting separation.

For the conventional fine-resolution light-curtain case, ANSI B11.19 uses an intrusion allowance of 14 mm; other resolutions or devices can require different values. Confirm the sensing resolution and applicable conditions in the purchased edition and the manufacturer's safety manual.

For example, measured total stopping time of 0.30 s gives S = 2000 × 0.30 + 14 = 614 mm. That is the baseline. The installed distance must be at least this result, measured from the sensing field to the hazard, and increased if the risk assessment identifies a credible reach, trapping or bypass route.

Establishing total stopping time

Total stopping time is often the weak point. It includes light-curtain response, safety relay or PLC processing, machine-control response and the mechanical, hydraulic or servo stopping time after a person breaks the beam.

Measure representative operation and use the worst credible result: full speed, maximum load, least favourable brake condition and applicable stopping path. Do not rely only on the drive catalogue value, and assess alternative control branches separately.

Keep test records, configured response times, machine speed, brake condition and final measured distance with the risk assessment. Changes to guarding, logic, speed, load or maintenance can invalidate the result, so review it after material plant or task changes.

Choosing the safeguarding arrangement

A light curtain works best where the hazard can be stopped directly and the sensing field covers every credible access route. Resolution must suit the hazard, and angled or recessed installations need scrutiny because beams can be bypassed.

Compare the main options before accepting the shortest distance:

Safeguarding option	Distance treatment	Design focus
Fine-resolution light curtain	Use S = K × T + C with the applicable intrusion term	Fast, direct machine stop and protected field
Coarse-resolution light curtain	Confirm resolution-based or device-specific C	Higher intrusion allowance and validated reach protection
Pressure-sensitive mat	Apply the prescribed intrusion and geometry method, not a 14 mm allowance	Floor coverage, creep-over and machine stopping
Fixed guard	Do not substitute S = K × T + C; verify openings and access prevention	Separation from the hazard throughout maintenance

The comparison is not permission to swap devices. A light curtain may suit an automated line, while a fixed guard can be stronger and simpler on an isolated pump. Selection belongs in the risk assessment, and the installation must withstand vibration, contamination and daily use.

Applying the calculation in Australia

Australian plants often combine an Australian OEM, imported machinery and older control retrofits. In a Melbourne engineering workshop, a new servo axis may stop quickly while an adjacent pneumatic ram remains slow. Assess each hazard independently rather than assigning one stopping time to the whole line.

Metric dimensions suit local drawings, but imported documents may use inches. Convert consistently and show units beside every time and distance. An engineer may call a guard “safe to use”, but that claim needs proof through the calculation, function testing and recorded acceptance.

On a Sydney production line or Brisbane construction machine, access can change during cleaning, maintenance and fault reset. Consider reaching over conveyors, crawling into frames and unexpected energisation. The separation must remain effective in realistic work, not only during commissioning.

Checks that prevent errors

Common errors include using drive stopping time instead of total system stopping time, mixing millimetres with inches, omitting C and measuring from the wrong reference point. Another is treating the minimum as the target, leaving no allowance for uncertainty or an unassessed access route.

Confirm that the distance applies to the hazardous point identified in the risk assessment. Where a hazard extends along a conveyor, an axis of motion or several crushing points, one straight-line number may not describe the installation. Protective field and stopping performance must match the geometry.

Use a second person to check inputs, arithmetic and physical measurements. A quality assurance check can prompt questions about coverage, bypass and maintenance, while the manufacturer's manual confirms device-specific assumptions. Record who approved the arrangement.

Get the standard for your safeguarding work

Engineers, safety professionals and compliance teams can obtain the ANSI B11.19 document as an immediate PDF download through the technical standards catalogue. The store supports multiple currencies and major payment methods. Choose the edition approved for your organisation and consider updates during periodic review.

Use the formula to set the minimum, test to establish stopping time, verify the separation and retain the evidence. Get the standard, document the assumptions and make the safeguarding arrangement safe to use in every normal operating mode.