Machine safeguarding misconceptions
How to keep workers out of harm’s way
This article highlights six key misconceptions about machine safeguarding. ANSI / ISO 12100:2012 Safety of machinery – General principles for design – Risk assessment and risk reduction is the primary reference.
Misconception #1: It’s complicated.
If a moving part on a machine may be touched and cause an injury, then that part must be safeguarded. The acronym AUTO reinforces the simplicity: Workers must not be able to reach Around, Under, Through or Over a guard to reach the danger zone of machines.
OSHA’s general guarding requirements for all machines at 1910.212(a)(1) expands on the simple concept to require: “One or more methods of machine guarding shall be provided to protect the operator and other employees in the machine area from hazards such as those created by point of operation, ingoing nip points, rotating parts, flying chips and sparks.”
Misconception #2: It’s a safety thing.
The American Board of Industrial Hygiene doesn’t allow IH maintenance certification points for CIHs that take machine guarding courses. The ABIH considers machine guarding to be primarily about preventing injury, not illness. This is far from true in modern thinking. ANSI / ISO 12100, informative Annex B, Examples of hazards, hazardous situations and hazardous events, lists ten type or group hazards. Group 1, Mechanical hazards, is the only group that deals exclusively with injury. Each of the other groups: 2 Electrical; 3 Thermal; 4 Noise; 5 Vibration; 6 Radiation; 7 Material/Substance; 8 Ergonomic, 9 Environment; and, 10 Combination, expand, often entirely, into hazards that may cause illness.
People that have a role in machine safeguarding include the machine designer, installer, operator, electrical and controls logic expertise, management, production, human resources, maintenance, housekeeping or janitorial services, worker representation, and where uncertainty exists, assistance from OSHA representatives with machine safeguarding experience.
Misconception #3: It’s about specifications.
Organizations such as ANSI, ISO, IEC, and NFPA have developed dozens of consensus standards and guidelines for machine safeguarding. Machine safeguarding is about performance not specifications, however. OSHA 1910.212(a)(3)(ii) says machine safeguarding shall be in conformity with any appropriate standards. If the specification in the standard is not protective, the employer must ensure adequate protection is provided. It’s performance: machine safeguarding must prevent worker injury or illness.
The problem with specifications is sometimes they’re not protective. Consider OSHA 1910.212(a)(5) Exposure of blades. “When the periphery of the blades of a fan is less than seven (7) feet above the floor or working level, the blades shall be guarded.” This is an outdated, but current, OSHA specification based upon the average height of servicemen in WWII at about 5’8.”
ANSI/RIA R15.06-1999 Industrial Robots and Robot Systems – Safety Requirements contained a specification of 12-inches for the lower dimension of perimeter guarding (fence). The updated standard, ANSI TR R15.406:2014, has the lower dimension at seven inches. What caused the change? Some workers could readily crawl under the 12-inch fence, but not the 7-inch fence.
If your organization needs to do something more protective, see ANSI / ISO 12100:2012 for risk assessment guidance.
Misconception #4: Workers are smart enough to stay out of machine danger zones.
Most often it’s workers who believe this misconception; especially when they’re caught bypassing or wrongly using a machine safeguard. Some supervisors turn a blind eye when workers do stupid things to achieve production goals. Prevention stops stupid.
Machine safeguarding must stay, almost exclusively, at the top rungs of hierarchy of controls. Eliminate the hazard. Engineer out the hazard. Administrative, training, and lesser controls, such as warning signs, discipline and hand tools, are very poor choices and rarely qualify as adequate machine safeguards. Make it impossible for workers to place any part of their body into machine danger zones.
Misconception #5: If one part of the machine cell is found to be adequately safeguarded, then all parts of the cell are safeguarded.
With increasing frequency, machines are being integrated, connected and automated to perform a series of work. Robotics often feed and unload parts from machines, such as presses. Even after being robotically unloaded, parts may be further machined, assembled or modified before reaching human hands. All integrated machinery within the cell, often with multiple human access points, must be safeguarded by door interlocks, barrier fencing, light curtains, and other safeguards, such as use of a teach pendant. If a worker enters the cell through any interlocked door or bypasses any other safeguard device, all machine danger zones within the cell must be controlled, such as by machine stoppage. OHS pros and other people testing functionality of machine safeguards should not fall to the misconception that if one cell safeguard works, they all work.
Misconception #6: Trust that machine safeguards have control reliability and redundancy upon a single failure.
PLC logic, electrical wiring, device builds, and other machine safeguards are impractical to test in the field. Single failure among any program, electrical, or mechanical device must be controlled by redundancy and other means. To demonstrate the adequacy of machine reliable controls requires review of product technical literature, reading schematics or blueprints, and other practices often performed by a controls or electrical engineer or other people with expertise in these matters – expertise generally outside of the OHS pro’s capabilities. If verification such as documented proof cannot be provided for reliable safeguard controls, then the OHS pro should consider machine safeguards to be inadequate.
Machine safeguarding is not complex when performed as a team, and it must be done by engineered prevention. Workers must never be given the freedom to put any part of their body into a machine’s danger zone. Finally, performance to prevent injury or illness trumps specifications when demonstrating machines are adequately safeguarded.