Machine Safety: hazard remediation, mechanical versus control system solutions

What's the residual risk for Cat 3 hazard mitigated by a fixed steel plate? Did the repair result in a control reliable solution? Are physical barriers or control solutions better to reduce risk. Five steps define the hierarchy of measures for hazard mitigation and machine safety risk reduction.


So, for a Cat 3 hazard mitigated by a fixed steel plate, what’s the residual risk? Cat 1? Would that be a control reliable solution? How come we can’t simplify the process for all? In my opinion, all of the machine safety and risk assessment standards approach the risk assessment and risk reduction process as somewhat complex. I’m talking about the entire process for a machine. Including the risk reduction measures to achieve acceptable residual risk for every hazard, mechanical or control system related.


The five steps of the “Hierarchy of Measures” for hazard mitigation begins with design it out:

1.) Eliminate the hazard – design it out

2.) Isolate the hazard with hard guarding

3.) Add additional engineering, guards, devices, or layers of safety

4.) Administrative controls like – training, signage, assessments, etc.

5.) Personal protective equipment (PPE) like - goggles, gloves, outer clothing, shields, etc. 

Arguably, steps 1, 2 and 3 can be focused at the mechanical design of the machine including the application of fixed guards. By now most risk assessment practitioners understand this and that they need to transition to the control system for additional hazard mitigation as needed to reach acceptable risk. Steps 4 and 5 are also considered as acceptable solutions for risk reduction.


However, don’t risk Categories (B, 1, 2, 3 & 4) only apply to the “control system”?  When you check out the Category descriptions you see words like; control reliable, single channel with monitoring, dual channel with monitoring, and more. Does this mean that machine safety hazards, other than those addressable via the control system, are only dangerous or not dangerous? 


When a fixed guard is applied over a hazard the standards say that tamper proof attachment devices should be used to prevent unauthorized persons from removing the guard. Okay, so I guess it’s dangerous or not! On the other hand, by applying a warning sign is the hazard dangerous or not? How do you rate or measure the risk reduction of a warning sign? In one standard hazard levels are described as; high, medium, low and negligible. Will that work for all hazards including the control system? Or, do you still need Categories for the control system? If you still need Categories for the control system how do you transition into and out of Categories during the risk reduction flow process? 


Perhaps the machine safety standards could take a look at covering all of the mechanical, electrical, control systems, and administrative solutions within their section titled something like “Risk Reduction Measures.” Then, there could be obvious transitions during the journey of the risk reduction flow process. I’ve seen many an end user having difficulty with this issue versus an original equipment manufacturer (OEM). But, the OEM isn’t necessarily concerned with this issue because he’s not the target of OSHA and the end user is most always concerned with Steps 4 and 5 of the Hierarchy of Measures.  


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, hazard remediation, mechanical versus control system solutions.


J.B. Titus, CFSERelated articles:

Machine Safety – does a risk assessment need to be updated for a minor modification to a machine?

Machine Guarding & The Hierarchy of Measures for Hazard Mitigation

Machine Safety – does OSHA reference consensus standards for compliance?

Machine Safety: Is OSHA okay with my 'acceptable' risk mitigation?


Contact: for “Solutions for Machine Safety”.

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