Force and injury — How hard is too hard? ISO/TR 21260 will help

Last updated on August 23rd, 2022 at 05:37 pm

For anyone involved in risk assessment and control, there are always questions regarding how much force it takes to injure a person. As a reminder, force is a vector quantity that has magnitude and direction and, if unopposed, will cause an object to change its velocity and direction.

As soon as we decided that products that hurt people were not OK, engineers wanted to know the limits on forces applied to people. These questions applied to airmen flying military fighters and submariners fighting below the surface in the US military. Divers that were used for tactical actions, salvage, repair and recovery missions needed to know how deep they could dive and for how long.

In the 1950s, the US military studied the forces that could be applied to the human body. Because volunteers were hard to come by, cadavers were used to test the forces necessary to puncture the skin, lacerate tissues, and amputate or crush various body parts. These tests were also done with pig cadavers. It was shown that cadavers don’t behave the way live people do and that the forces and speeds needed to create a particular injury were highly variable.

Since those days, scientists and engineers have continued to study these questions. A key application that is bringing this work to the forefront is collaborative robotics. The industrial applications are many, from using the speed and discrimination of robots to aid humans in assembly tasks to the strength and precision that robots can add to a work task.

Collaborative Robots – early years

In the early 2000s, researchers were working on ways to limit speeds, forces and joint torques to try to protect workers. I made a little video mashup to give you an idea of where things were then.

One important area for future development outside of the industry is in healthcare. There are many applications where robots can offer humans help, including surgery and patient care. Patient care workers often suffer back injuries from assisting patients in getting in and out of bed or to the toilet. There are manual hoists that can be used for these purposes, but to use them, a patient care worker is needed every time. Patient care work is often very intimate since patients may need significant help to bathe or toilet properly.

A collaborative healthcare robot could be used in these cases instead of a human worker, bringing extra speed and strength and eliminating the chance of injury or abuse by or to the patient and the care worker. Here are a few examples of the types of assistance I’m thinking about as I write.

Healthcare is a growing area for these types of personal assistance robots.

Today’s applications

Since then, the potential for all kinds of physical forms of collaborative robots has developed. Here’s another short video mashup of where things are today.

More information needed

All of this work is great, but coming back to injury prevention is key. The Boston Dynamics Spot Mini is great at avoiding hitting people and objects, but many applications require robot-to-person contact. ISO/TC 199 started a project in 2012 to develop a new standard to help guide machine designers with respect to the level of force that people can tolerate.

Led by Professor Yoji Yamada from Nareda University in Japan, ISO/TC 199/WG12, Human-machine interactions, is starting a new development phase for ISO/TR 21260, now titled Safety of machinery — Mechanical safety data for physical contacts between moving machinery or moving parts of machinery and persons, formerly titled “Safety of machinery — Mechanical safety data for physical contacts between moving machinery or moving parts of machinery and persons.” ISO/TC 199 converted ISO 21260 to a Technical Report and changed the title at the end of April 2020 due to challenges with achieving consensus on the document’s content. Conversion to a TR will help to get the document published so that readers can start to work with the concepts included in the document.

ISO/TC 199/WG12 in Denmark, 2019
ISO/TC 199/WG12 in Denmark, 2019

ISO/TR 21260 is entering a new development stage following the end of its development as an International Standard. The Technical report is planned to be published by the end of April 2023.

ISO/TC 199/WG12 in Tokyo, Japan, December 2019
Professor Yamada 4th from left

ISO/TR 21260 Scope

The scope of a Technical Report tells you what the document covers and may provide specific exclusions.

1 Scope

This document specifies force and energy related limits for physical contacts between the machine or parts of the machine and people that are caused by movement of the machine or parts of the machine as part of its intended use or foreseeable misuse.

This document covers all types of machines that are designed to function where people can be present and the machine can make physical contact with those people.

This document deals with contact between machines or parts of a machine and people during their normal interaction as part of their function and contact not necessary for the functioning of the machine. It encompasses interactions that are intentional or unintentional.

This document is limited to defining threshold values to avoid harm caused by physical contact.

This document does not cover effects from contact due to

  • burning
  • electrical shock
  • cutting or any risk due to contact with a dangerous tool used or supported by the machine
  • additional effects due to the contact causing a fall

How will this Technical Report help designers?

The standard focuses on assisting designers in applying the first level of the Hierarchy of Controls; Inherently Safe Design. The standard deals specifically with the machine’s forces and not thermal or electrical effects, all of which require more study.

The Technical Report is expected to be published by April 2023. You can follow the RSS feed for the document by visiting You’ll see the icon for the RSS feed next to the “General Information” heading. You can follow the RSS feed using any feed reader, like Feedly or your web browser.

ISO/TS 15066 – Collaborative Robots

ISO 21260 is one of two documents that are destined to hold important places as we develop closer physical relationships with our robotic creations. The second document was developed by ISO/TC 299, Robotics, and is currently an ISO Technical Specification (TS). ISO/TS documents are used by Technical Committees to publish information that is believed to be important to the sector served by a TC, but which has not yet developed to the stage where it can be standardized. ISO/TS 15066:2016, Robots and robotic devices — Collaborative robots (RSS feed), applies to industrial robot systems as described in ISO 10218-1 (RSS feed) and ISO 10218-2 (RSS feed). It does not apply to non-industrial robots, although the safety principles presented can be useful to other areas of robotics. The document specifies safety requirements for collaborative industrial robot systems and the work environment and supplements the requirements and guidance on collaborative industrial robot operation given in ISO 10218-1 and ISO 10218-2.

If you are involved in the development of collaborative robots, these documents are required reading. They will also be useful to anyone designing collaborative robotic applications since the force limits will be very helpful during risk assessment of the application.

If you have any questions regarding the documents or their development, please email me or leave a comment below.


Update 2020-10-31: The work on ISO/TR 21260 is set to restart with a meeting in Dec-20. The seed document for the work is the last draft prepared during the original development cycle, which is good news as losing that progress would have been a bad thing. More updates to follow when I can tell you more about the progress in the Working Group.

Update 2020-10-02: TL;DR – Work on ISO/TR 21260 was stopped for a while because the project had exceeded the development timeline allowed by ISO. In March 2020, a communication indicated that a decision would be made at the next ISO/TC 199 Plenary meeting, scheduled for the fall of 2020. With the global pandemic, a decision was made to change ISO 21260 from an International standard to a Technical Report (TR). According to the ISO/IEC Directives, Part 2, a Technical Report is defined as:

Technical Report

document (3.1.1) published by ISO or IEC containing collected data of a different kind from that normally published as an International Standard (3.1.4) or Technical Specification (3.1.5)

Note 1 to entry: Such data may include, for example, data obtained from a survey carried out among the national bodies, data on work in other international organizations or data on the ?state of the art (3.4)? in relation to standards of national bodies on a particular subject.

Note 2 to entry: Prior to mid-1999, Technical Reports were designated as Technical Reports of type 3.

ISO/IEC Directives, Part 2

This change allows development to continue without the loss of the work done in the project. Publication of ISO/TR 21260 is now anticipated at the end of April 2023, although it is possible that it could be published before then.

This post was updated 2020-06-10 with new information on ISO/TR 21260.

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5 thoughts on “Force and injury — How hard is too hard? ISO/TR 21260 will help

  1. Good Effort!, this new Standard will be valuable for this specific item. Do you have available an advance about the force-injury results? Right now I am facing with a risk assessment trying to determine the maximum possible injury arising form a 866 N force coming from a pallet on a turntable rotating at a 784 mm/s speed. Is it possible to reach the team in order to send an email regarding my question? Thanks in advance!

    1. Hi Juan,

      I don’t have access to the kind of data you’re seeking, unfortunately. The document is still being developed, with an expected publication date of 2023-04-28, presuming it makes it through the review process. The first attempt at getting the standard published failed and the project has been restarted as of the end of April this year. Until the public review draft is published again, you’ll have to wait to see the content.

      With respect to your risk assessment challenge, in my experience, a force of the magnitude you describe and the speed you describe is a significant hazard. Safeguarding of some kind around that hazard is required.

  2. The robot integrators are designed and programmed to understand the motion of force control, they do corporate well along with robotic machinery system. They need to be programmed with loop processing in order to perform.

  3. The robot integrators are designed and programmed to understand the motion of force control, they do corporate well along with robotic machinery system. They need to be programmed with loop processing in order to perform.

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