Machine Safeguarding for an Imperfect Workforce: Humans.


Expertise Includes:

    • Machine Design & Safeguarding
    • Machinery & Equipment Analysis
    • Products Liability
    • Risk Assessment

Every day more than 12 people in the United States lose their lives in workplace injuries, according to U.S. Department of Labor data. In 2011, OSHA estimates, 3.3 million people suffered a workplace injury from which they may never fully recover. Two of the top ten most frequently cited OSHA standards that result in injuries and death are lockout/tagout and machine guarding.

S-Roll drive guarded with an interlocked cage.

The Safety Hierarchy states that elimination of hazards by design is the most effective means of injury prevention. If a hazard can’t be eliminated, safeguards should be incorporated. If a safeguard isn’t feasible, then warnings should be issued about hazards and risks of the equipment. Employee training and procedures such as a lockout/tagout policy are the last — and least effective — injury prevention option.

While it’s true a properly implemented lockout/tagout policy provides a high degree of protection, it has one weakness that cannot be overcome. There’s a 100 percent probability all employees will not follow the policy at all times. That’s particularly the case when workers must perform minor, routine and repetitive servicing activities that are integral to production operation.

Alternative measures to lockout/tagout that should be considered as effective protection for machines requiring minor servicing during normal production operations are interlocked guards, presence-sensing devices and two-hand controls. Interlocked guards prevent the machine from operating when a barrier guard is opened or removed. A presence-sensing device prevents the machine from operating if someone is in harm’s way, and a two-hand control prevents the machine from being operated until both of the operator’s hands are on the two-hand control out of harm’s way.

There’s more to these incidents than simply faulting workers. The bigger picture may include the design and manufacturing of the machine itself. The machine design should tolerate errors and mistakes in human behavior when technologically and economically feasible. The science of human behavior demonstrates errors and mistakes are inevitable. The proof is in annual OSHA reports of on-the-job deaths and injuries in American workplaces. Expecting workers to be perfect is unrealistic.

Failure to provide an interlocked guard on a machine that should have one is a design defect that can lead to a products liability claim against the machine manufacturer. Safe machine designs are those that forgive worker errors and mistakes, and allow them to go home at the end of the workday — alive and fully intact.

Jeffery H. Warren, PhD, PE, CSP, is the chief engineer and CEO at Warren specializing in mechanical, machine design and safety. His deep expertise in machine design and safety analysis makes him a frequent presenter, trainer and expert witness. In addition to investigating more than 2000 claims involving property damage and injuries related to machinery and equipment since 1987, Jeff has an undergraduate degree in Mechanical Engineering from the University of North Carolina as well as a Master of Science and a Doctorate in Mechanical Engineering from Virginia Polytechnic Institute and State University — both with machine design emphasis.

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