Berke on Safety: Safe But Slow: How Long ‘Til Operators Remove the Guard?

Oct. 23, 2008
Operators of a nip-roll system with a barrier guard find they must remove the machine’s guard a few times each shift to clear obstructions.

How many jams do you think it will take before they start skipping the lockout-tagout (LO/TO) procedures, or before they leave the guard off entirely? And how long after that until there’s a serious mishap?

Machine guarding protects people from injury during a machine’s normal operation. But guard designers must also anticipate reasonably foreseeable activities outside normal operation. Hazard and job-safety analyses, close-call reporting programs, and OSHA 300 injury-reporting logs can point the way to designing and implementing comprehensive guarding. A haphazard approach will not protect workers from injury or a company from an OSHA citation.

There are four basic approaches to machine guarding: barrier guards, guarding devices, guarding by location, and warnings. In my opinion, warnings, even if they meet ANSI Z535 and are accompanied by pictograms, should not be a worker’s sole protection. Guarding by location, another permissible but inferior method, means placing machinery so no one can contact the machine’s hazards. Managers should conduct a thorough safety analysis for each application, know the ANSI and OSHA standards for guarding by location, and go beyond them to ensure safety.

The best protection for the worker is a barrier guard, a physical barrier between a hazard and anyone in close proximity to it. The concept is simple; the devices may not be. Each guard’s design is an exercise in human-factors analysis. As seen in the opening example, barrier guards that slow production or hamper equipment use will be removed in short order.

The best barrier guards are built into their machines. If a fixed guard must be fastened into position, use fasteners that require a tool to install or remove; wing nuts cannot be used.

When a barrier guard is not feasible, designers might turn to guarding devices. These include light screens, two-palm antilock pushbuttons, interlocks, and pullbacks. They don’t keep the worker from touching the machinery, but they do stop any moving hazards before worker can make contact.

Installers must set up guarding devices properly, taking into account how long it takes the moving hazard to stop and how fast a person’s hand can move. The device must be triggered and the machine stopped before the person can touch it.

For example, consider a light screen protecting a nip roller. The light screen must sit so that when a person breaks the light rays, the nip roll can stop before their hand can get into harm’s way.

Sometimes a fixed guard and a guarding device must be combined. The opening example is one of those where OSHA allows an interlock to be used with a fixed guard. This does not mean OSHA lets operators replace just any LO/TO program with an interlock. Instead, OSHA requires strict procedures for situations like these, as detailed in the Letters of Interpretation available at

Lanny Berke is a registered professional engineer and Certified Safety Professional involved in forensic engineering since 1972. Got a question about safety? You can reach Lanny at [email protected].

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