Trapped Key Interlocking

This entry is part 3 of 7 in the series Guards and Guard­ing

Many machine design­ers think of inter­locks as exclu­sive­ly elec­tri­cal devices; a switch is attached to a mov­able mechan­i­cal guard, and the switch is con­nect­ed to the con­trol sys­tem. Trapped Key Inter­lock­ing is a way to inter­lock guards that is equal­ly effec­tive, and often more appro­pri­ate in dif­fi­cult envi­ron­men­tal con­di­tions. Con­tin­ue read­ing “Trapped Key Inter­lock­ing”

Q & A: Category 2 and Testing Intervals

This entry is part 1 of 2 in the series Q & A

Dur­ing the Free Safe­ty Talks that we did with Schm­er­sal Cana­da and Franklin Empire, we had a “hot ques­tion” come up regard­ing Cat­e­go­ry 2 archi­tec­ture and the test­ing inter­val require­ment. In the short video below, Doug answers that ques­tion.

If you have more ques­tions or felt some­thing wasn’t clear in the video, leave us a com­ment and we will get back to you!

If you are hav­ing prob­lems with devel­op­ing your safe­ty func­tion, please get in touch with Doug direct­ly.

Notes

Email Doug direct­ly.

References

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

[2]     “The Bath­tub Curve and Prod­uct Fail­ure Behav­ior (Part 2 of 2)”, Weibull.com, 2018. [Online]. Avail­able: http://www.weibull.com/hotwire/issue22/hottopics22.htm. [Accessed: 13- May- 2018].

[3]    Ger­man Social Acci­dent Insur­ance (DGUV) — Insti­tute for Occu­pa­tion­al Safe­ty and Health (BGIA), “Func­tion­al safe­ty of machine con­trols — Appli­ca­tion of ISO 13849–1 — Report 2/2008e”, Insti­tute for Occu­pa­tion­al Safe­ty and Health (BGIA), Sankt Augustin, DE, 2008.

[4]     “Safe­ty Cir­cuit Exam­ples of Safe­ty Com­po­nents | Tech­ni­cal Guide | Aus­tralia | Omron IA”, Omron.com.au, 2018. [Online]. Avail­able: http://www.omron.com.au/service_support/technical_guide/safety_component/safety_circuit_example.asp. [Accessed: 14- May- 2018].

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Acknowl­edge­ments: ISO, OMRON, oth­ers as cit­ed.
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Five reasons you should attend our Free Safety Talks

Reason #1 — Free Safety Talks

You can’t argue with Free Stuff! Last week we part­nered with Schm­er­sal Cana­da and Franklin Empire to put on three days of Free Safe­ty Talks. We had full hous­es in all three loca­tions, Wind­sor, Lon­don and Cam­bridge, with near­ly 60 peo­ple par­tic­i­pat­ing.

We had two great pre­sen­ters who helped peo­ple under­stand Pre-Start Health and Safe­ty Reviews (PSRs) [1], CSA Z432-2016 [2], Inter­lock­ing Devices [3] and Fault Mask­ing [4].

Mr Vashi at Franklin Empire Cambridge
Mr Vashi at Franklin Empire Cam­bridge

Franklin Empire pro­vid­ed us with some great facil­i­ties and break­fast to keep our minds work­ing. Thanks, Franklin Empire and Ben Reid who orga­nized all of the reg­is­tra­tions!

Mr Nix discussing injury rates in machine modes of operation
Mr Nix dis­cussing injury rates in machine modes of oper­a­tion

Reason #2 — Understanding Interlocking Devices

A portrait of Mr Kartik Vashi
Mr Kar­tik Vashi, CFSE

Mr Kar­tik Vashi, CFSE, dis­cussed the ISO Inter­lock­ing Device stan­dard, ISO 14119. This stan­dard pro­vides read­ers with guid­ance in the selec­tion and appli­ca­tion of inter­lock­ing devices, includ­ing the four types of inter­lock­ing devices and the var­i­ous cod­ing options for each type. Did you know that ISO 14119 is also direct­ly ref­er­enced in CSA Z432-16 [2]? That means this stan­dard is applic­a­ble to machin­ery built and used in Cana­da as of 2016. If you don’t know what I’m talk­ing about, you can con­tact Mr Vashi to get more infor­ma­tion.

ISO 14119 Fig 2 showing some aspects of different types of interlocking devices.
ISO 14119 Fig 2 show­ing some aspects of dif­fer­ent types of inter­lock­ing devices [3]

Reason #3 — Understanding Fault Masking

Mr Vashi also talked about fault mask­ing, an impor­tant and often mis­un­der­stood sit­u­a­tion that can occur when inter­lock­ing devices or oth­er electro­mechan­i­cal devices, like emer­gency stop but­tons, are daisy-chained into a sin­gle safe­ty relay or safe­ty input on a safe­ty PLC. Mr Vashi drew from ISO/TR 24119 to help explain this phe­nom­e­non. If you don’t under­stand the impact that daisy-chain­ing inter­lock­ing devices can have on the reli­a­bil­i­ty of your inter­lock­ing sys­tems, Mr Vashi can help you get a han­dle on this top­ic.

A part of ISO 24119 Fig 2 showing one method of daisy-chaining interlocking devices.
A part of ISO 24119 Fig 2 show­ing one com­mon method of daisy-chain­ing inter­lock­ing devices [4]

Reason # 4 — Pre-Start Health and Safety Reviews

Portrait of Doug Nix, C.E.T.
Mr Doug Nix, C.E.T.

Mr Nix opened his pre­sen­ta­tion with a dis­cus­sion of some com­mon­ly asked ques­tions about Pre-Start Health and Safe­ty Reviews (PSRs). There are many ways that peo­ple become con­fused about the WHY, WHAT, WHEN, WHERE, WHO and HOW of PSRs, and Mr Nix cov­ered them all. This unique-to-Ontario process requires an employ­er to have machines, equip­ment, rack­ing and process­es reviewed by a Pro­fes­sion­al Engi­neer or anoth­er Qual­i­fied Per­son when cer­tain cir­cum­stances exist (see O. Reg. 851, Sec­tion 7 Table). If you are con­fused by the PSR require­ments, con­tact Mr Nix for help with your ques­tions.

Reason #5 — Understanding the changes to CSA Z432

CSA Z432 [2] was updat­ed in 2016 with many changes. This much-need­ed update came after 12 years expe­ri­ence with the 2004 edi­tion and many changes in machin­ery safe­ty tech­nol­o­gy. Mr Nix briefly explored the many changes that were brought to Cana­di­an machine builders in the new edi­tion, includ­ing the many new ref­er­ences to ISO and IEC stan­dards. These new ref­er­ences will help Euro­pean machine builders get their prod­ucts accept­ed in Cana­di­an mar­kets. Both Mr Vashi and Mr Nix sit on the CSA Tech­ni­cal Com­mit­tee respon­si­ble for CSA Z432.

Reason #6 — Hot Questions

We like to over-deliv­er, so here’s the bonus rea­son!

We had some great ques­tions posed by our atten­dees, two of which we are answer­ing in video posts this week. If you have ever con­sid­ered using a pro­gram­ma­ble safe­ty sys­tem for lock­out, our first video explains why this is not yet a pos­si­bil­i­ty. Mr Nix gets into some of the reli­a­bil­i­ty con­sid­er­a­tions behind the O.Reg. 851 Sec­tions 75 and 76 and CSA Z460 require­ments.

Mr Nix post­ed a sec­ond video dis­cussing ISO 13849–1 [5] Cat­e­go­ry 2 archi­tec­ture require­ments and par­tic­u­lar­ly Test­ing Inter­vals. This video explains why it is not pos­si­ble to meet the test­ing require­ments using a pure­ly electro­mechan­i­cal design solu­tion.

Edit: 16-May-18

A case in the UK illus­trates the dan­gers of bypass­ing inter­lock­ing sys­tems. A work­er was killed by a con­vey­or sys­tem in a pre-cast con­crete plant when he was work­ing in an area nor­mal­ly pro­tect­ed by a key-exchange sys­tem. Here’s the link to the arti­cle on OHSOnline.com. Allow­ing work­ers into the dan­ger zone of a machine with­out oth­er effec­tive risk reduc­tion mea­sures may be a death sen­tence.

References

[1]     Ontario Reg­u­la­tion 851, Indus­tri­al Estab­lish­ments

[2]     Safe­guard­ing of Machin­ery. CSA Z432. 2016.

[3]     Safe­ty of machin­ery — Inter­lock­ing devices asso­ci­at­ed with guards — Prin­ci­ples for design and selec­tion. ISO 14119. 2013.

[4]     Safe­ty of machin­ery — Eval­u­a­tion of fault mask­ing ser­i­al con­nec­tion of inter­lock­ing devices asso­ci­at­ed with guards with poten­tial free con­tacts. ISO/TR 24119. 2015.

[5]     Con­trol of haz­ardous ener­gy — Lock­out and oth­er meth­ods. CSA Z460. 2013.

[6]     Safe­ty of machin­ery — Safe­ty-relat­ed parts of con­trol sys­tems — Part 1: Gen­er­al prin­ci­ples for design. ISO 13849–1. 2015.

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Acknowl­edge­ments: Kar­tik Vashi, ISO, Franklin Empire, S more…
Some Rights Reserved