Machine Safety

An ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis, operating efficiencies and cost savings, as well as all relevant safety standards, such as those from NFPA, ANSI, RIA, IEC, ISO and OSHA. About J.B. Titus.

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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.

September 20, 2013


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 



For more than 30 years, J.B. Titus has advised a wide range of clients on machine functional safety solutions, including Johnson + Johnson, Siemens, General Motors, Disney, Rockwell Automation, Bridgestone Firestone, and Samsung Heavy Industries. He holds a Bachelor of Business Administration degree from Oklahoma University in industrial management and an MBA from Case Western Reserve University in marketing and finance. He is a professional member of the American Society of Safety Engineers and is OSHA-certified in machine guarding. Titus is also TUV-certified as a Functional Safety Expert and serves on several American National Standards Institute, National Fire Protection Association, and National Electrical Manufacturers Association national safety and health standards committees. Reach him at jb(at)jbtitus.com and via www.jbtitus.com.