Palletizing cell safety requirements: what each standard asks for and which documents to demand

A person walking covers 1,600 millimeters in one second. With that figure, which ISO 13855 uses as approach speed according to Leuze’s summary of the 2024 edition, you decide how far away a light curtain goes. Palletizing cell safety requirements are built from calculations like that one and from signed documents, and each one falls to someone different. This text is informational and does not replace legal advice or your plant’s risk assessment.

What are the palletizing cell safety requirements?

The NOM (Norma Oficial Mexicana, a mandatory federal standard) is binding and the STPS, Mexico’s federal labor ministry, enforces it (section 10). ISO standards on their own are not law in Mexico, although your corporate office or your contract can require them; confirm this with your legal team. Keep an eye on PROY-NOM-004-STPS-2020 (DOF, February 8, 2021), the draft revision, which already mentions ISO 13849 as a way to estimate the required level. The Ministry of Economy still lists it as a draft and the 1999 standard as in force (checked November 3, 2026).

If you run a food plant, one clarification: according to ISO, Part 2 excludes hygiene requirements, food processing and conditions such as freezing outside the manufacturer’s specification. Those risks get reviewed separately.

What NOM-004 puts on the employer

This comes from the DOF text and the STPS guide (December 2022):

• Potential risk study (5.2). An inventory of hazardous conditions, with type of harm, severity and probability.
• Specific program (5.3 and chapter 7). Make it known and enforce it. Item 7.1 g requires that feeding and removing product not be a risk factor: in your cell, the infeed of empty pallets and the outfeed of full ones.
• Training (5.4). The Target Academy course, one week in its own lab with groups of 6 and included with the machine, can feed into it; the obligation stays with the employer.
• Maintenance (7.2). Frequency and procedure, guards back in place, energy lockout with tag and padlock, and a dated record kept for at least 12 months. We go through this in FANUC robot preventive maintenance.
• Guards and devices (chapter 8). Among other conditions: an emergency stop that is easy to activate, and a failure of power or of the device itself must not create a risk or let the cycle start.

Hiring a verification unit (unidad de verificación, a private body approved to check NOM compliance) is optional (9.1), and its report lasts five years, unless guards or devices are modified (9.4). The study and the program belong to the employer, with the inputs your supplier gives you.

Where do the safeguards and the light curtain go?

FANUC starts from a fence with an interlocked door that stops the robot when it opens (M-410iB/140H manual, B-83164EN/04, March 2017). Bypassing that door’s signal is ruled out: the controller manual calls it very dangerous (B-83195EN/08, February 2016). Troax, a safeguard manufacturer, summarizes ISO 13857:2019 this way: a structure under 1,400 mm calls for additional measures, and the gap between floor and safeguard does not exceed 180 mm (May 2020).

For the light curtain, the formula is S = (K × T) + C. S is the distance to the danger zone; K, the approach speed; T, the total stopping time; C, a margin that depends on resolution. Datalogic gives K of 1,600 mm/s and C of 850 mm for curtains of 40 to 70 mm resolution (undated catalog, indicative summary; the current edition of ISO 13855 is 2024). With T of 0.5 seconds, S comes to 1,650 mm; with T of 1 second, 2,450 mm. That is a Target Robotics calculation with those assumptions, and each tenth of a second of stopping time adds 160 mm of floor.

That time gets measured. FANUC publishes stopping times and distances as reference values, and asks you to measure your own because they vary with the robot, the load and the program (M-20iB manual, September 2018). The type of stop counts too. In the R-30iB standard stop pattern, the emergency stop cuts power (category 0), and opening the door in automatic produces a controlled stop (category 1), which takes longer; motor power-off can be delayed up to 2 seconds, and FANUC asks that those seconds go into the risk assessment (B-83164EN/04, 2017). Ask which stop pattern your controller has before accepting the light curtain’s position.

Two situations deserve their own line in the assessment. With the mode switch in teach mode, the door is disabled and the programmer answers for keeping everyone else out; the manual calls for removing the key before opening. And if your integrator uses Dual Check Safety, software that limits motion to defined zones and cuts motor power if the robot crosses them, ask for the configuration in print. FANUC Europe presents it as a way to save floor space (checked November 3, 2026); every zone has to appear in the assessment. If your own people are going to set it up, Target Academy teaches a DCS course.

How does the pallet pass without stopping the cell?

The pallet has to go in and out without taking production down. Muting exists for that: detectors in sequence that expect an object of a certain size and shape, and briefly suspend the part of the curtain it passes through (DigiKey, May 13, 2021). Banner, a light curtain manufacturer, shows it in depalletizing: the pallet crosses and the cell keeps running (checked November 3, 2026).

There is a mechanical reason as well. FANUC warns that frequent power-off stops can cause problems in the robot, and gives as a bad example an area sensor or a safety mat that trips as a matter of routine (B-83164EN/04, 2017).

With the integrator and under controlled conditions, test it the way someone in a hurry would use it: a person right up against the pallet, or pulling a pallet jack. DigiKey warns of another risk, the person who crosses, stops the machine and restarts it from inside, and suggests putting the reset outside the protected zone. Muting gets validated with the pallet and with a person, because the curtain only knows what its detectors tell it.

What is PL and who decides which one your cell needs?

PL stands for performance level: a band of probability of dangerous failure per hour, from a, the least demanding, to e (SICK, July 20, 2022). ISO 13849-1:2023 gives the design method and makes clear that it does not set which functions or which required PL to use in each application. That required level comes out of the risk assessment, with three questions: how severe the injury would be, how often someone is exposed and whether it can be avoided. The PL the function achieves must be equal or higher.

The 2025 edition of ISO 10218 reinforces that logic. According to SICK (September 8, 2025), the previous edition asked for PL d across the board and the new one asks for a PL per function, based on the risk assessment. A3 (March 20, 2025) adds that Part 2 talks about the application, with workpiece, program and equipment included. The PL of each function is justified with your cell’s risk assessment, and you can ask for that sheet.

The achieved level can be calculated with SISTEMA, free software from IFA/DGUV; version 3 matches the 2023 edition (updated October 31, 2025).

What “in accordance with” and “certified” mean

An outside body issues certificates, and ISO makes clear that it neither certifies nor issues them. When someone tells you “certified,” ask for the document with holder, scope and number. The UL 508A program has its own limit: the certification covers the panel, without the loads or the equipment it controls (UL, spring 2025).

At Target Robotics we say two things with these words: “Safety functions designed in accordance with ISO 13849-1” and “Control panels built under the UL 508A program.” The first describes how the functions are designed; the second, the program under which the panel is built. Neither is a certificate for the complete cell and neither replaces the study NOM-004 requires of the employer.

Which documents and equipment to ask the integrator for

If you are going to compare proposals, add these lines to the sheet in how to compare palletizer quotes. If the cell comes from a manual handling problem, NOM-036, Mexico’s federal standard on manual handling, goes in the same file, and the robotic palletizer gets quoted with that data.

What if you change product, gripper or stacking pattern?

According to A3, the application includes the workpiece, the program and the equipment that supports it. A new gripper, a heavier case or a pattern that raises the pallet height can shift hazards, stopping times and distances.

NOM-004 requires preserving safety conditions when equipment is modified or rebuilt (7.2.2 b), and a verification unit’s report loses validity if guards or devices change (9.4). The 2020 draft would go further: repeat the analysis when the machine changes location, undergoes an alteration or adds an element (section 5.2 of the draft).

Today, ask for the date of your last risk assessment and compare it with the date of your last change of gripper, stacking pattern or program.