Machine Safety: Discourage the defeating of safety interlocks

There are people who intentionally defeat safety interlocks. Doesn’t this increase risk and hazard level? See 6 proactive actions to discourage disabling of safety interlocks, along with one additional technology-based solution.


Omron safety door switchesYou’re kidding me. Do you mean to say there actually are people who intentionally defeat safety interlocks? Doesn’t this mean that they have increased the hazard level?

Yes, there are folks in manufacturing who defeat safe guards, and safety interlocks are a prime example of such safe guards. 

Machines or workcells have various types of access doors. There are fixed removable access doors, which are typically only removed for some level of maintenance procedures. In some cases these doors could have safety interlocks installed.

Another type of access doors are those designed and installed as removable and/or can be opened on a routine basis. Examples include: tooling set-up or adjustment, clean out of the work area for such things as swarf on metal cutting machines, working an awkwardly-shaped work piece or to perform a secondary manual operation simultaneously with a primary automated operation. Such access doors typically have safety interlocks installed to signal a safety-related function.

Omron STI interlock switchUpon inspection of a manufacturing area, either type of access door often have safety interlocks defeated with the intent of speeding up an activity. In some cases it may be because personnel around these machines have become so intimate with their surroundings that they feel they can safely operate the machines without guards. They may think they can take appropriate precautions because they’re all too aware of the hazards. In these cases, is management turning a blind eye to this practice? 

Of course, “safety culture” are the first two words that come to mind.

The first thing I think of is a quote from Bill Hilton, director of health and safety at Georgia-Pacific: “A historical lack of accidents does not imply a current presence of safety. It simply means you’ve been faster than the machine." 

So, what are some pro-active actions to consider for discouraging defeating of safety interlocks?

1. Update and/or conduct a risk assessment of your machine(s).

2. Review your safety culture to insure that it doesn’t allow dangerous behaviors.

3. Evaluate the design of access doors to make sure that all conditions are met.

4. Train personnel and conduct audits on proper procedures.

5. Document and keep required records current.

6. Consider a certified safety controller to monitor your safe interlocks. 

On this final potential action of a safety certified controller, one best practice could include installing safety interlocks with both opposing normally open and normally closed contacts. The safety controller could then monitor the state and health of each set of contacts. An abnormal state would then automatically cause a safe state of operation for the machine with appropriate alarms annunciated. 

Don’t we agree that most owners of manufacturing businesses don’t typically sleep well thinking their employees are properly protected because they will always be faster than the machine? Injuries do not improve productivity.

Has this presented you with any new perspectives? Add your comments or thoughts to the discussion by submitting your ideas, experiences, and challenges in the comments section below.

J.B. Titus, CFSE

Related articles:

Machine Safety – designing a safe machine begins with Risk Assessment!

Machine Guarding & The Hierarchy of Measures for Hazard Mitigation

Machine Safety – serious machine guarding issues!

ASSE - Professional Safety Journal- Near-Miss Reporting, May 2013

OSHA – search for near miss 

Charles , MT, United States, 10/10/13 12:26 PM:

In the early 1970s, while working in a stamping house, I noticed that punch-press die-protection systems were being bypassed by the press operators. These workers were annoyed at press stoppage because their production bonuses would suffer (and they did not pay any penalty for crashes).

The protective systems lacked “test for opens/test for shorts” methodology, which I designed into all similar personnel, equipment and production safety automation from that time forward. The concept behind that methodology became the foundation of a dynamic logic system, “Natural Machine Logic,” which results in automation designs that are safer, faster, and use less than 1% of the components of a microprocessor-based system.
Anonymous , 12/06/13 09:51 AM:

Am I the only person who believes that safety at any cost is driving jobs to other countries. If you owned a company would you want to deal with OSHA and the rest of the bureaucrats, lawyers and everybody else that wants a piece of your pie by burdening you with their profession. I am 60 year old plant engineer who defeats many of the safeties. I do this so that I can quickly assess the problem, fix and get the machine back on line that feeds my family.

I am selling my house. I am told that not only my city has to inspect my house, but now the fire department has to inspect. More fees. In my county, they want to install home sprinkler systems in new houses.

As soon as someone says safety, every bureaucrat and lawyer wants money and my life is no better. It just adds to aggravation.

I am not against safety and feel it is very important to teach that safety is smart. But with the attitudes that are pushed in these articles, electricity nor gas would be in your house, airplanes would not fly overhead and cars would not be on streets.

I like my electricity, my heat, my car and flying. Sooner or later, you have to push back.
Bob , United States, 12/09/13 11:21 AM:

How will your family be fed the day you defeat the safety and get injured on the job?
Safety is not about OSHA. It's about caring enough about yourself and your people by making a safe workplace an absolute right. The benefits of a safe workplace are that it is a more productive workplace that stays in business longer at a lower cost.
So contrary to your initial point, I think it's things like safety that have helped drive jobs BACK to the U.S. Add up the costs of safety and logistics and transportation and quality and you see why wages and regulations no longer drive jobs away; in many ways they protect the value of U.S. manufacturing in a competitive global environment.
Bob Vavra
Content Manager
Plant Engineering
Anonymous , 12/12/13 12:41 PM:

I agree with you Bob 100% - as a safety professional this is a challenge that every employer faces and I fully support your POV.
Anonymous , 12/03/14 01:51 PM:

Planes and other machines are safer nowadays because it evolves. We were aware of safety importance and we improve it. Are more accessible and worth to be used to such extent.
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