Machinery Safety 101
3 July, 2018

Trapped Key Interlocking

by Doug Nix
in Control Functions, Functional Safety, Hazardous Energy Control Procedures, Interlocks, Interlocks /
6 Comments
This is a trapped key interlock on the door of an electrical switchgear cabinet. To open the door the key must be inserted and turned to withdraw a bolt that holds the door closed. With the bolt withdrawn, the key is held in the lock. The upstream switching device is held open by another interlock using the same key; since the key can only be in one of the two locks, it prevents accidentally closing the upstream switch while the cabinet is open for maintenance. The interlock is attached to the door with one-way screws to discourage casual removal of the lock, which would defeat the system.
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…

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15 May, 2018

Five reasons you should attend our Free Safety Talks

by Doug Nix
in Events, Free Talks, Functional Safety, Hazardous Energy Control Procedures, Interlocks, Interlocks, ISO 13849, Lockout, News, Ontario, Pre-Start Health and Safety Reviews, Standards /
No Comments
Banner for the 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…

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29 May, 2015

Presence Sensing Devices – Reaching over sensing fields

by Doug Nix
in Canada, Guards and Guarding, Hierarchy of Controls, Ontario, Robotics /
No Comments
This entry is part 2 of 7 in the series Guards and Guard­ing

I recently heard about an applic­a­tion ques­tion related to a light cur­tain where a small gap exis­ted at the top of the sens­ing field, between the last beam in the field and the…

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27 January, 2014

CSA Z432 Safeguarding of Machinery – 3rd Edition

by Doug Nix
in Canada, Control Functions, Control Reliability, Emergency Stop, Functional Safety, Guards and Guarding, Hazards, Hierarchy of Controls, Interlocks, Risk Assessment, Standards /
No Comments

If you build machinery for the Cana­dian mar­ket, or if you modi­fy equip­ment in Cana­dian work­places, you will be famil­i­ar with CSA Z432, Safe­guard­ing of Machinery. This stand­ard has been…

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3 August, 2012

Get the Basics Right!

by Doug Nix
in Canada, CE Mark, Control Reliability, Functional Safety, General, Hazards, Hierarchy of Controls, International, ISO 13849, Risk Assessment, Robotics, Seminars, USA /
No Comments

For more than 15 years I’ve been teach­ing people about risk assess­ment, machinery safety and CE Mark­ing of machinery in private, onsite classes and through present­a­tions at safety con­fer­ences. Things are…

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16 July, 2012

New HSE advice on CE marking assemblies of machinery

by Doug Nix
in CE Mark, EU European Union /
No Comments
Guarded machinery in a plant

This post was ori­gin­ally pub­lished on machinebuilding.net. Reprin­ted with per­mis­sion. By Jon Severn, machinebuilding.net A degree of con­fu­sion sur­rounds the ques­tion of CE mark­ing assem­blies of machinery under the Machinery Dir­ect­ive 2006/42/EC.…

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1 June, 2012

Interlocking Devices: The Good, The Bad and the Ugly

by Doug Nix
in Canada, CE Mark, Components, Control Functions, Control Reliability, EU European Union, EU Robotics, Guards and Guarding, Hierarchy of Controls, Interlocks, Interlocks, International, International Robotics, ISO 13849, North American Robotics, Ontario, Robotics, USA /
7 Comments
This entry is part 1 of 7 in the series Guards and Guard­ing

Note: A short­er ver­sion of this art­icle was pub­lished in the May-2012 edi­tion of  Man­u­fac­tur­ing Auto­ma­tion Magazine. When design­ing safe­guard­ing sys­tems for machines, one of the basic build­ing blocks is the…

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21 June, 2011

Hockey Teams and Risk Reduction or What Makes Roberto Luongo = PPE

by Doug Nix
in Canada, Control Functions, EU European Union, General, Guards and Guarding, Hazards, Hierarchy of Controls, International, Risk Assessment /
5 Comments
Canucks Hockey Flag
This entry is part 2 of 5 in the series Hier­archy of Con­trols

Spe­cial Co-Author, Tom Doyle Last week we saw the Boston Bru­ins earn the Stan­ley Cup. I was root­ing for the green, blue and white, and the ruin of my voice on…

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28 February, 2011

Understanding the Hierarchy of Controls

by Doug Nix
in Canada, CE Mark, Complementary Protective Measures, Control Functions, Control Reliability, Emergency Stop, EU European Union, Functional Safety, General, Guards and Guarding, Hazardous Energy Control Procedures, Hierarchy of Controls, Interlocks, Interlocks, Lockout, Ontario, Risk Assessment, Robotics, USA /
8 Comments
The Hierarchy of Controls illustrated as an inverted triangle with each level of the hierarchy written one above the other, starting with Inherently Sfe design, then Engineering Controls, then Information for Use, then Administrative Controls and finally descending to PPE at the bottom. An arrow with the text "Effectiveness" on it runs parallel to the triangle and points downward from Inherently safe design to PPE.
This entry is part 4 of 5 in the series Hier­archy of Con­trols

(Eds. note: This art­icle was ori­gin­ally writ­ten in 2011 and was updated in Nov. 2018.) The “Hier­archy of Con­trols” is one approach to risk reduc­tion that has become entrenched in…

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