ISO 13849 Analysis — Part 1: Start with Risk Assessment

This entry is part 1 of 6 in the series How to do a 13849-1 analysis

I often get questions from clients about how to get started on Functional Safety using ISO 13849. This article is the first in a series that will walk you through the basics of using ISO 13849. Keep in mind that you will need to hold a copy of the 3rd edition of ISO 13849-1 [1] and the 2nd edition of ISO 13849-2 [2] to use as you go along. There are other standards which you may also find useful, and I have included them in the Reference section at the end of the article. Each post has a Reference List. I will publish a complete reference list for the series with the last post.

Where to start?

So you have just learned that you need to do an ISO 13849 functional safety analysis. You have the two parts of the standard, and you have skimmed them, but you are feeling a bit overwhelmed and unsure of where to start. By the end of this article, you should be feeling more confident about how to get this job done.

Step 1 – Risk Assessment

For the purpose of this article, I am going to assume that you have a risk assessment for the machinery, and you have a copy for reference. If you do not have a risk assessment, stop here and get that done. There are several good references for that, including ISO 12100 [3], CSA Z432 [4], and ANSI B11.TR3 [5]. You can also have a look at my series on Risk Assessment.

The risk assessment should identify which risks require mitigation using the control system, e.g., use of an interlocked gate, a light curtain, a two-hand control, an enabling device, etc.See the MS101 glossary for detailed definitions. Each of these becomes a safety function. Each safety function requires a safety requirements specification (SRS), which I will describe in more detail a bit later.

Safety Functions

The 3rd edition of ISO 13849 [1] provides two tables that give some examples of safety function characteristics [1, Table 8] and parameters [1, Table 9] and also provides references to corresponding standards that will help you to define the necessary parameters. These tables should not be considered to be exhaustive – there is no way to list every possible safety function in a table like this. The tables will give you some good ideas about what you are looking for in machine control functions that will make them safety functions.

While you are identifying risk reduction measures that will use the control system for mitigation, don’t forget that complementary protective measures like emergency stop, enabling devices, etc. all need to be included. Some of these functions may have minimum requirements set by Type B2 standards, like ISO 13850 [6] for emergency stop which sets the minimum performance level for this function at PLc.

Selecting the Required Performance Level

ISO 13849-1:2015 provides a graphical means for selecting the minimum Performance Level (PL) required for the safety function based on the risk assessment. A word of caution here: you may feel like you are re-assessing the risk using this tool because it does use risk parameters (severity, frequency/duration of exposure and possibility to avoid/limit harm) to determine the PL. Risk assessment This tool is not a risk assessment tool, and using it that way is a fundamental mistake. Its output is in terms of performance level, which is failure rate per hour of operation. For example, it is entirely incorrect to say, “This machine has a risk level of PLc” since we define PLs in terms of probable failure rate per hour.

ISO 13849-1 graphical selection tool for determining PLr requirement for a safety function
Graphical Performance Level Selection Tool [1]
Once you have assigned a required Performance Level (PLr) to each safety function, you can move on to the next step: Developing the Safety Requirements Specification.

Book List

Here are some books that I think you may find helpful on this journey:

[0]     B. Main, Risk Assessment: Basics and Benchmarks, 1st ed. Ann Arbor, MI USA: DSE, 2004.

[0.1]  D. Smith and K. Simpson, Safety critical systems handbook. Amsterdam: Elsevier/Butterworth-Heinemann, 2011.

[0.2]  Electromagnetic Compatibility for Functional Safety, 1st ed. Stevenage, UK: The Institution of Engineering and Technology, 2008.

[0.3]  Overview of techniques and measures related to EMC for Functional Safety, 1st ed. Stevenage, UK: Overview of techniques and measures related to EMC for Functional Safety, 2013.

References


[1]     Safety of machinery — Safety-related parts of control systems — Part 1: General principles for design. 3rd Edition. ISO Standard 13849-1. 2015.

[2]     Safety of machinery — Safety-related parts of control systems — Part 2: Validation. 2nd Edition. ISO Standard 13849-2. 2012.

[3]      Safety of machinery — General principles for design — Risk assessment and risk reduction. ISO Standard 12100. 2010.

[4]     Safeguarding of Machinery. CSA Standard Z432. 2004.

[5]     Risk Assessment and Risk Reduction- A Guideline to Estimate, Evaluate and Reduce Risks Associated with Machine Tools. ANSI Technical Report B11.TR3. 2000.

[6]    Safety of machinery — Emergency stop function — Principles for design. ISO Standard 13850. 2015.

Workplace Risk Assessment – CSA Z1002: Love it, Hate it, Tweak it

CSA Z1002 CoverThe CSA Z1002 TC Needs to Know: Love it, Hate it, Tweak it?

We need to know: Do you Love CSA Z1002? Hate CSA Z1002? Does it need some tweaking? We have a survey so you can let us know!

The First of Its Kind

In 2012, CSA published the first OHS Risk Assessment Standard of its kind: CSA Z1002, Occupational health and safety — Hazard identification and elimination and risk assessment and control. This standard has been in use in Canadian workplaces for four years now, and the Technical Committee is considering the need for updates and improvements to this important standard.

Key to the Z1000 Family

Z1002 is a key member of the Z1000 OHS Management System family of standards because it provides a central tool used in all of the other standards: Risk Assessment. Because it holds this central role, it’s important that it work smoothly and effectively, providing the kind of information that all of the other standards need to do their parts in reducing workplace risk.

The origins of Z1002 come from the machinery safety world where risk assessment is well developed, but the methods presented were broadened to allow their use in many other areas. Were they broadened enough? Could they be improved? These are important questions!

Influencing Other Standards

Shop Floor Hazard Identification
Shop Floor Inspection

The Significance of Z1002 in the Z1000 family has given it additional influence in other CSA OHS standards, including CSA Z432 Safeguarding of Machinery, CSA W117.2 Safety in Welding, Cutting, and Allied Processes, and even in CSA Z614 Children’s Playspaces and Equipment! This kind of influence puts even greater pressure on the standard, and the Technical Committee, to provide the kind of solid, reliable guidance needed.

The Second Edition

In order for the Technical Committee to move on to revising the standard and producing a Second Edition, we need input from the user community. We have heard a bit from some users, but we really want to hear from YOU. CSA has created a very brief survey that you can take to let the TC know how you are using the standard, if it’s doing the job for you, and what you think needs trashing, polishing, or tweaking. We REALLY want to hear from you, so please, take a few minutes and answer the survey! You’ll feel all warm and fuzzy because you did, and we’ll get some good ideas about what to do with the future edition of Z1002! Sound like a good deal? I thought so!

Got questions about this? You can always contact me: dnix@complianceinsight.ca.

CSA Z432 Third Edition Open for Public Review!

CSA Z432, Safeguarding of Machinery, is the basic standard for Canada when it comes to most types of machinery. Only Power Presses and Press Brakes, and Industrial Robots are covered separately in their own standards. CSA Z432 provides guidance on important topics, like:

  • Risk Assessment
  • Risk reduction through the Hierarchy of Controls
  • Guard design requirements
  • Safeguarding device application requirements, and
  • Instructions and information for use

This standard should be used by everyone in Canada responsible for the safe design of machinery used in Canadian workplaces, and for the safety of workers who use machinery in their daily tasks.

CSA has just opened public review on CSA Z432, Safeguarding of Machinery, third edition. If you are a user, a builder of machinery, or an evaluator of machinery, this is your opportunity to see the draft of this important standard, and to make comments to help the Technical Committee improve the standard on your behalf.

To access the public review copy, you must register on CSA’s Public Review system. Registration is free and allows you to get read-only access to the drafts of all new standards that CSA is preparing to publish. The time you take to read and comment on new standards is very valuable to the Technical Committees, as it helps us to correct areas where misunderstandings or confusion may exist, and to add material where it is needed.

See the Draft

Review closes 2-Jan-2016, so don’t delay!

If you need more information, please contact Jill Collins at CSA Group.