ISO 13849 – 1 Analysis — Part 1: Start with Risk Assessment

This entry is part 1 of 7 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.