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Machine Safety: System degradation and incidence of injury

Are older hardwired safety systems less safe than newer integrated safety systems? (See table.) Since 2002 when integrated safety automation was introduced for machine safety, a growing awareness has emerged questioning the effectiveness over time of a hardwired / hardware safety system versus an integrated safety system. What is the ultimate effectiveness of a safety-related function comparing the date of commissioning to a date several years later given the two approaches?

February 17, 2012


JB Titus, CFSESince 2002 when integrated safety automation was introduced for machine safety, a growing awareness has emerged questioning the effectiveness over time of a hardwired / hardware safety system versus an integrated safety system. What is the ultimate effectiveness of a safety-related function comparing the date of commissioning to a date several years later given the two approaches?

   I’ve been asked this question many times over the past 10 years causing me to do some research. So far I haven’t been successful in finding comparative data for example on the incidence of injuries for:

1)   Newly commissioned hardwired / hardware safety systems performing safety-related functions.

2)   Versus, (for example) 10-year-old hardwired / hardware safety systems performing safety-related functions.

   Nor have I found any convincing data on the incidence of injuries comparing hardwired versus integrated (software / firmware) safety systems. What I have found via research, multiple interviews, and personal experience is that the answer usually boils down to the eventual safety culture discussion. I believe the ultimate answer lies in the “Mean Time To Fail Dangerous” (MTTFD) comparison of the two approaches. Most everyone agrees that both approaches are arguably equal at date of commissioning (new) in their effectiveness and reliability to perform the intended safety-related function. However, the safety culture issue could be the determinate factor to differentiate their comparative effectiveness and reliability over time. This comparison, in my opinion, is represented in the table below.

 

Comparing older versus newer machine safety systems

Hardwired / Hardware Safety Systems

 

 

 

Integrated Safety Systems

 

Inflexible – no software

 

Flexibility

 

Flexible via software

 

Few to none

 

Diagnostics

 

System provided at HMI

 

Significant un-planned downtime with high trouble shoot time

 

Downtime

 

Minimal un-planned downtime with low trouble shoot time

 

Broken / loose cables

 

Intermittent breakdown

 

60 to 80 percent fewer cables

 

Insecure access

 

System integrity

 

Levels of access security

 

Finite

 

MTTFD

 

10-8

 

Increases over time

 

Maintenance

 

Constant over time

 

 

This discussion is intended to create some cognitive thinking concerning the question of effectiveness and reliability of the intended safety-related function given the two approaches and the lack of supporting incidence data. Additionally, we have abundant supporting testimonials today that report reduced costs and increased productivity with integrated versus hardwired safety systems. This of course depends on the size, complexity, and number of machines on the plant floor.

   As a plant manager, you’re the one responsible individual who can evaluate your safety culture and choose the best alternative approach for machine safety for your business.

   Are older hardwired safety systems less safe than newer integrated safety systems? Your comments or suggestion are always welcome so please let us know your thoughts. Submit your ideas, experiences, and challenges on this subject in the comments section below. Click on the following text if you don't see a comments box, then scroll down: Machine Safety: System degradation and incidence of injury.

Safety matters logo.   Related articles:

Updating Minds About Machine Safety

Machine Safety Culture – compliance versus cooperation driven

Machine Safety – the myths of safety cultures.

   Contact: www.jbtitus.com for “Solutions for Machine Safety”.



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.